Re: Intdir early review of draft-ietf-intarea-gue-06

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



Hello folks,

Attached, please find a file containing more specific editorial suggestions and observations, along with a rfcdiff-generated file that highlights the differences from the current version of draft-ietf-intarea-gue.

I am not expert in some areas that are important for this draft, and I did not read the companion documents that were cited.  I will appreciate any further discussion to help my understanding on those points, and will be happy to have further interaction on any of the suggestions that I have made.

Regards,
Charlie P.


On 2/28/2019 7:00 PM, Charles Perkins wrote:
Reviewer: Charles Perkins
Review result: Almost Ready

This document needs an applicability statement which includes the assumptions
and the reasons it might be useful.  Deliverability needs to be expanded.
Reasons why middleboxes would be unlikely inspect GUE fields might be included.

For instance, the discussion in second paragraph of 5.11.1 belongs in the
applicability statement.

It should also be explained why arbitrary GUE extensions are less likely to be
filtered out compared to IPv6 destination options.
============================================== The document assumes close
familiarity with deployment scenarios that seem to be characterized by acronyms
such as RSS, aRFS, TSO, LRO, etc.  While I am pretty familiar with a lot of
encapsulation techniques, I had to study the meaning of these acronyms.  If it
is intended to effectively restrict the intended audience, that is O.K., but
otherwise more background is needed along with relevant citations.
============================================== [GUEEXTENS] is cited in a way
that places a normative dependency on [GUEEXTENS].  So, [GUEEXTENS] belongs in
the Normative References. ============================================== I have
a large number of specific comments which I will post shortly in the form of a
rfcdiff-generated file.


Internet Area WG                                              T. Herbert
Internet-Draft                                                Quantonium
Intended status: Standard track                                  L. Yong
Expires March 4, 2019                                         Huawei USA
                                                                  O. Zia
                                                               Microsoft
                                                         August 31, 2018

                       Generic UDP Encapsulation
                       draft-ietf-intarea-gue-06

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.  

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress." 

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt 

   The list of Internet-Draft Shadow Directories can be accessed at 
   http://www.ietf.org/shadow.html

   This Internet-Draft will expire on March 4, 2019.

Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors. All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document. Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.
<!-- CEP: duplicate boilerplate!!  -->

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
 


Herbert, Yong, Zia        Expires March, 2019                   [Page 1]

Internet Draft         Generic UDP Encapsulation         August 31, 2018


   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.









































 


Herbert, Yong, Zia        Expires March, 2019                   [Page 2]

Internet Draft         Generic UDP Encapsulation         August 31, 2018


Abstract          

   This specification describes Generic UDP Encapsulation (GUE), which
   uses UDP to encapsulate packets of various Internet
   protocols for transport across layer 3 networks. By encapsulating
   packets in UDP, specialized capabilities in networking hardware for
   efficient handling of UDP packets can be used. GUE provides
   basic encapsulation methods suitable for higher level constructs, such
   as tunnels and overlay networks for network virtualization.
   GUE provides extensibility by allowing optional data fields within
   the encapsulation, and is generic in that it can encapsulate
   packets of various Internet protocols.
<!--  CEP: This means GUE is "flexible", not "generic".  Oh well.  -->
<!--  CEP: "generic" would mean that GUE offers a vanilla solution
           relevant to other encapsulation protocols.  -->

Table of Contents

   1. Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .  5
     1.1. Terminology and acronyms  . . . . . . . . . . . . . . . . .  5
     1.2.  Requirements Language  . . . . . . . . . . . . . . . . . .  6
   2. Base packet format  . . . . . . . . . . . . . . . . . . . . . .  7
     2.1. GUE variant . . . . . . . . . . . . . . . . . . . . . . . .  7
   3. Variant 0 . . . . . . . . . . . . . . . . . . . . . . . . . . .  8
     3.1. Header format . . . . . . . . . . . . . . . . . . . . . . .  8
     3.2. Proto/ctype field . . . . . . . . . . . . . . . . . . . . .  9
       3.2.1 Proto field  . . . . . . . . . . . . . . . . . . . . . .  9
       3.2.2 Ctype field  . . . . . . . . . . . . . . . . . . . . . . 10
     3.3. Flags and extension fields  . . . . . . . . . . . . . . . . 11
       3.3.1. Requirements  . . . . . . . . . . . . . . . . . . . . . 11
       3.3.2. Example GUE header with extension fields  . . . . . . . 11
     3.4. Private data  . . . . . . . . . . . . . . . . . . . . . . . 12
     3.5. Message types . . . . . . . . . . . . . . . . . . . . . . . 13
       3.5.1. Control messages  . . . . . . . . . . . . . . . . . . . 13
       3.5.2. Data messages . . . . . . . . . . . . . . . . . . . . . 13
     3.6. Hiding the transport layer protocol number  . . . . . . . . 13
   4. Variant 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
     4.1. Direct encapsulation of IPv4  . . . . . . . . . . . . . . . 15
     4.2. Direct encapsulation of IPv6  . . . . . . . . . . . . . . . 16
   5. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
     5.1. Network tunnel encapsulation  . . . . . . . . . . . . . . . 17
     5.2. Transport layer encapsulation . . . . . . . . . . . . . . . 17
     5.3. Encapsulator operation  . . . . . . . . . . . . . . . . . . 18
     5.4. Decapsulator operation  . . . . . . . . . . . . . . . . . . 18
       5.4.1. Processing a received data message  . . . . . . . . . . 18
       5.4.2. Processing a received control message . . . . . . . . . 19
     5.5. Router and switch operation . . . . . . . . . . . . . . . . 19
     5.6. Middlebox interactions  . . . . . . . . . . . . . . . . . . 20
       5.6.1. Inferring connection semantics  . . . . . . . . . . . . 20
       5.6.2. NAT . . . . . . . . . . . . . . . . . . . . . . . . . . 20
     5.7. Checksum Handling . . . . . . . . . . . . . . . . . . . . . 20
 


Herbert, Yong, Zia        Expires March, 2019                   [Page 3]

Internet Draft         Generic UDP Encapsulation         August 31, 2018


       5.7.1. Requirements  . . . . . . . . . . . . . . . . . . . . . 21
       5.7.2. UDP Checksum with IPv4  . . . . . . . . . . . . . . . . 21
       5.7.3. UDP Checksum with IPv6  . . . . . . . . . . . . . . . . 22
     5.8. MTU and fragmentation . . . . . . . . . . . . . . . . . . . 22
     5.9. Congestion control  . . . . . . . . . . . . . . . . . . . . 22
     5.10. Multicast  . . . . . . . . . . . . . . . . . . . . . . . . 23
     5.11. Flow entropy for ECMP  . . . . . . . . . . . . . . . . . . 23
       5.11.1. Flow classification  . . . . . . . . . . . . . . . . . 23
       5.11.2. Flow entropy properties  . . . . . . . . . . . . . . . 24
     5.12 Negotiation of acceptable flags and extension fields  . . . 25
   6. Motivation for GUE  . . . . . . . . . . . . . . . . . . . . . . 26
     6.1. Benefits of GUE . . . . . . . . . . . . . . . . . . . . . . 26
     6.2 Comparison of GUE to other encapsulations  . . . . . . . . . 26
   7. Security Considerations . . . . . . . . . . . . . . . . . . . . 28
   8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 28
     8.1. UDP source port . . . . . . . . . . . . . . . . . . . . . . 28
     8.2. GUE variant number  . . . . . . . . . . . . . . . . . . . . 29
     8.3. Control types . . . . . . . . . . . . . . . . . . . . . . . 29
   9. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 29
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 30
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 30
     10.2. Informative References . . . . . . . . . . . . . . . . . . 30
   Appendix A: NIC processing for GUE . . . . . . . . . . . . . . . . 33
     A.1. Receive multi-queue . . . . . . . . . . . . . . . . . . . . 33
     A.2. Checksum offload  . . . . . . . . . . . . . . . . . . . . . 34
       A.2.1. Transmit checksum offload . . . . . . . . . . . . . . . 34
       A.2.2. Receive checksum offload  . . . . . . . . . . . . . . . 35
     A.3. Transmit Segmentation Offload . . . . . . . . . . . . . . . 35
     A.4. Large Receive Offload . . . . . . . . . . . . . . . . . . . 36
   Appendix B: Implementation considerations  . . . . . . . . . . . . 36
     B.1. Privileged ports  . . . . . . . . . . . . . . . . . . . . . 37
     B.2. Setting flow entropy as a route selector  . . . . . . . . . 37
     B.3. Hardware protocol implementation considerations . . . . . . 37
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 38














 


Herbert, Yong, Zia        Ex++pires March, 2019                   [Page 4]

Internet Draft         Generic UDP Encapsulation         August 31, 2018


1. Introduction

   This specification describes Generic UDP Encapsulation (GUE) which is
   a general method for encapsulating packets of arbitrary IP protocols
   within User Datagram Protocol (UDP) [RFC0768] packets. Encapsulating
   packets in UDP facilitates efficient transport across networks.
   Networking devices often provide protocol specific processing and
   optimizations for UDP packets. Packets for
   IP protocols not typically parsed by networking hardware can be
   encapsulated in UDP packets to maximize deliverability and to
   engage flow specific mechanisms for routing and packet steering.

   GUE provides an extensible header format for including optional data
   in the encapsulation header. This data can cover items such
   as the virtual networking identifier, security data for validating or
   authenticating the GUE header, congestion control data, etc.
<!--  CEP: citations needed.  Plus I am surprised yet another
           validation mechanism is needed!  -->
                                                                GUE also
   allows private optional data in the encapsulation header. This
   feature can be used by a site or implementation to define local
   custom optional data, and allows experimentation of options that may
   eventually become standard.

   This document does not define any specific GUE extensions. [GUEEXTEN]
   specifies a set of initial extensions.

   The motivation for the GUE protocol is described in section 6.

1.1. Terminology and acronyms

<!--  CEP:  Need terminology for "connection semantics".  -->
<!--  CEP:  Need terminology for "flow entropy".  -->
<!--  CEP:  Need terminology for "Canonical length".  -->

   GUE              Generic UDP Encapsulation

   GUE Header       A variable length protocol header that is composed
                    of a primary four byte header and zero or more four
                    byte words for optional header data

   GUE packet       A UDP/IP packet that contains a GUE header and GUE
                    payload within the UDP payload

   GUE variant      A version of the GUE protocol or an alternate form
                    of a version

   Encapsulator     A network node that encapsulates packets in GUE

   Decapsulator     A network node that decapsulates and processes
                    packets encapsulated in GUE

   Data message     An encapsulated packet in the GUE payload that is
                    addressed to the protocol stack for an associated
                    protocol
 


Herbert, Yong, Zia        Expires March, 2019                   [Page 5]

Internet Draft         Generic UDP Encapsulation         August 31, 2018


   Control message  A formatted message in the GUE payload that is
                    implicitly addressed to the decapsulator to monitor
                    or control the state or behavior of a tunnel

   Flags            A set of bit flags in the primary GUE header

   Extension field
                    An optional field in a GUE header whose presence is
                    indicated by corresponding flag(s)

   C-bit            A single bit flag in the primary GUE header that
                    indicates whether the GUE packet contains a control
                    message or data message

   Hlen             A field in the primary GUE header that gives the
                    length of the GUE header

   Proto/ctype      A field in the GUE header that holds either the IP
                    protocol number for a data message or a type for a
                    control message

   Private data     Optional data in the GUE header that can be used for
                    private purposes

   Outer IP header  Refers to the outer most IP header or packet when
                    encapsulating a packet over IP

   Inner IP header  Refers to an encapsulated IP header when an IP
                    packet is encapsulated

   Outer packet     Refers to an encapsulating packet  

   Inner packet     Refers to a packet that is encapsulated

1.2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].









 


Herbert, Yong, Zia        Expires March, 2019                   [Page 6]

Internet Draft         Generic UDP Encapsulation         August 31, 2018


2. Base packet format

   A GUE packet is comprised of a UDP packet whose payload is a GUE
   header followed by a payload which is either an encapsulated packet
   of some IP protocol or a control message such as an OAM (Operations,
   Administration, and Management) message. A GUE packet has the general
   format:

   +-------------------------------+
   |                               |
   |        UDP/IP headers         |
   |                               |
   |-------------------------------|
   |                               |
   |         GUE Header            |
   |                               |
   |-------------------------------| 
   |                               |                              
   |      Encapsulated packet      |
   |      or control message       |
   |                               |
   +-------------------------------+
<!--  CEP: This representation seems upside down compared to normal.
           Maybe even horizontal would be better...  -->

   The GUE header has variable length, as determined by the presence of
   optional extension fields.

2.1. GUE variant

   The first two bits of the GUE header contain the GUE protocol variant
   number. The variant number can indicate the version of the GUE
   protocol as well as alternate forms of a version.

   Variants 0 and 1 are described in this specification; variants 2 and
   3 are reserved.














 


Herbert, Yong, Zia        Expires March, 2019                   [Page 7]

Internet Draft         Generic UDP Encapsulation         August 31, 2018


3. Variant 0

   Variant 0 indicates version 0 of GUE, and defines a generic
   extensible format to encapsulate packets by Internet protocol number.

3.1. Header format

   The header format for variant 0 of GUE in UDP is:
<!--  CEP: Is it possible to have a GUE *not* in UDP?
           If not, then the wording above is curious...  -->

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+\
   |        Source port            |      Destination port         | |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ UDP
   |           Length              |          Checksum             | |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+/
   | 0 |C|   Hlen  |  Proto/ctype  |             Flags             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   ~                  Extensions Fields (optional)                 ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   ~                    Private data (optional)                    ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The contents of the UDP header are:

      o Source port: If connection semantics (section 5.6.1) are applied
        to an encapsulation, this is set to the local source port for
        the connection. When connection semantics are not applied, the
        source port is either set to a flow entropy value as described
        in section 5.11, or it should be set to the GUE assigned port
        number, 6080.

      o Destination port: If connection semantics (section 5.6.1) are
        applied to an encapsulation, this is set to the destination port
        for the tuple. If connection semantics are not applied this is
        set to the GUE assigned port number, 6080.
<!--  CEP: Why not always use the former?  -->

      o Length: Canonical length of the UDP packet (length of UDP header
        and payload).

      o Checksum: Standard UDP checksum (handling is described in
        section 5.7).


 


Herbert, Yong, Zia        Expires March, 2019                   [Page 8]

Internet Draft         Generic UDP Encapsulation         August 31, 2018


   The GUE header consists of:

      o Variant: 0 indicates GUE protocol version 0 with a header.

      o C: C-bit: When set indicates a control message, not set
        indicates a data message.

      o Hlen: Length in 4-byte words of the GUE header, including
        optional extension fields but not the first four bytes of the
        header. Computed as (header_len - 4) / 4, where header_len is
        the total header length in bytes. All GUE headers are a multiple
        of four bytes in length. Maximum header length is 128 bytes.

      o Proto/ctype: When the C-bit is set, this field contains a
        control message type for the payload (section 3.2.2). When the
        C-bit is not set, the field holds the Internet protocol number
        for the encapsulated packet in the payload (section 3.2.1). The
        control message or encapsulated packet begins at the offset
        provided by Hlen.

      o Flags: Header flags that may be allocated for various purposes
        and may indicate presence of extension fields. Undefined header
        flag bits MUST be set to zero on transmission.

      o Extension Fields: Optional fields whose presence is indicated by
        corresponding flags. 

      o Private data: Optional private data block (see section 3.4). If
        the private block is present, it immediately follows the last
        extension field present in the header. The private block is
        considered to be part of the GUE header. The length of this data
        is determined by subtracting the starting offset from the header
        length.
<!--  CEP: not clear why it's better to be part of the GUE header, than
           another kind of extension field.  -->

3.2. Proto/ctype field

   The proto/ctype fields either contains an Internet protocol number
   (when the C-bit is not set) or GUE control message type (when the C-
   bit is set).

3.2.1 Proto field

   When the C-bit is not set, the proto/ctype field MUST contain an IANA
   Internet Protocol Number. The protocol number is interpreted relative
   to the IP protocol that encapsulates the UDP packet (i.e. protocol of
   the outer IP header).
<!--  CEP: Presumably this means IPv4 or IPv6, but it's the same for
           either of those. -->
                          The protocol number indicates
   the type of the next protocol header which is contained in the GUE
   payload at the offset indicated in Hlen. Intermediate devices MAY
 


Herbert, Yong, Zia        Expires March, 2019                   [Page 9]

Internet Draft         Generic UDP Encapsulation         August 31, 2018


   parse the GUE payload per the number in the proto/ctype field, and
   header flags MUST NOT affect the interpretation of the proto/ctype
   field.

<!--  CEP: There are three possibilities below.  They should be itemized. -->
   When the outer IP protocol is IPv4, the proto field MUST be set to a
   valid IP protocol number usable with IPv4. An
   exception is that the destination options extension header using the
   PadN option MAY be used with IPv4 as described in section 3.6. The
   "no next header" protocol number (59) also MAY be used with IPv4 as
   described below.
<!--  CEP: should cite the website for IP protocol numbers:
https://www.iana.org/assignments/protocol-numbers/protocol-numbers.xhtml
  -->

   When the outer IP protocol is IPv6, the proto field can be set to any
   defined protocol number except that it MUST NOT be set to Hop-by-hop
   options (number 0). 
<!--  CEP: Please explain the rationale for this restriction. -->
                       If a received GUE packet in IPv6 contains a
   protocol number that is an extension header (e.g. Destination
   Options) then the extension header is processed after the GUE header
   is processed as though the GUE header is an extension header.

   IP protocol number 59 ("No next header") can be set to indicate that
   the GUE payload does not begin with the header of an IP protocol.
   This would be the case, for instance, if the GUE payload were a
   fragment when performing GUE level fragmentation. The interpretation
   of the payload is performed through other means (such as flags and
   extension fields), and intermediate devices MUST NOT parse packets
   based on the IP protocol number in this case.
<!--  CEP: This cannot be enforced.  -->

3.2.2 Ctype field

   When the C-bit is set, the proto/ctype field MUST be set to a valid
   control message type. A value of zero indicates that the GUE payload
   requires further interpretation to deduce the control type. This
   might be the case when the payload is a fragment of a control
   message, where only the reassembled packet can be interpreted as a
   control message.

   Control messages are defined in an IANA registry. Control message
   types 1 through 127 may be defined in standards. Types 128 through
   255 are reserved to be user defined for experimentation or private
   control messages.
<!--  CEP: For types 1 --> 127, need to specify how to allocate.
           Why not mandate standards action?  -->

   This document does not specify any standard control message types
   other than type 0. Type 0 does not define a format of the control
   message. Instead, it indicates that the GUE payload is a control
   message, or part of a control message (as might be the case in GUE
   fragmentation), that cannot be correctly parsed or interpreted
   without additional context.
<!--  CEP: The latter needs an example.  The former seems to follow
           from network mishandling of IPv6 fragmentation.  -->
 


Herbert, Yong, Zia        Expires March, 2019                  [Page 10]

Internet Draft         Generic UDP Encapsulation         August 31, 2018


3.3. Flags and extension fields

   Flags and associated extension fields are the primary mechanism of
   extensibility in GUE. As mentioned in section 3.1, GUE header flags
   indicate the presence of optional extension fields in the GUE header.
   [GUEEXTENS] defines an initial set of GUE extensions.

3.3.1. Requirements

   There are sixteen flag bits in the GUE header. Flags may indicate
   presence of an extension fields. The size of an extension field
   indicated by a flag MUST be a fixed constant.

<!--  CEP: "paired" means 2.  Need another term.  Perhaps "combined". -->
   Flags can be paired together to allow different lengths for an
   extension field. For example, if two flag bits are paired, a field
   can possibly be three different lengths-- that is bit value of 00
   indicates no field present; 01, 10, and 11 indicate three possible
   lengths for the field. Regardless of how flag bits are paired, the
   lengths and offsets of optional fields corresponding to a set of
   flags MUST be well defined.

   Extension fields are placed in order of the flags. New flags are to
   be allocated from high to low order bit contiguously without holes.
   Flags allow random access, for instance to inspect the field
   corresponding to the Nth flag bit, an implementation only considers
   the previous N-1 flags to determine the offset. Flags after the Nth
   flag are not pertinent in calculating the offset of the field for the
   Nth flag. Random access of flags and fields permits processing of
   optional extensions in an order that does not depend on their position
   in the packet.

   Flags (or paired flags) are idempotent such that new flags MUST NOT
<!--  CEP: This is not what "idempotent" means.  -->
   cause reinterpretation of old flags. Also, new flags MUST NOT alter
   interpretation of other elements in the GUE header nor how the
   message is parsed (for instance, in a data message the proto/ctype
   field always holds an IP protocol number as an invariant).

   The set of available flags can be extended in the future by defining
   a "flag extensions bit" that refers to a field containing a new set
   of flags.
<!--  CEP: The extension bit should be specified in this document. -->

3.3.2. Example GUE header with extension fields

   An example GUE header for a data message encapsulating an IPv4 packet
   and containing the Group Identifier and Security extension fields
   (both defined in [GUEEXTENS]) is shown below: 


 


Herbert, Yong, Zia        Expires March, 2019                  [Page 11]

Internet Draft         Generic UDP Encapsulation         August 31, 2018


    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | 0 |0|    3    |      94       |1|0 0 1|          0            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Group Identifier                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                           Security                            +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
<!--  CEP: The 'C' bit should be a 1, right?  Otherwise the 94
           has to be an IPv6 protocol number.  -->

   In the above example, the first flag bit is set which indicates that
   the Group Identifier extension is present which is a 32 bit field.
   The second through fourth bits of the flags are combined flags that
   indicate the presence of a Security field with seven possible sizes.
   In this example 001 indicates a sixty-four bit security field.
<!--  CEP: This seems to make the GUEEXTENS document normative. -->

3.4. Private data

   An implementation MAY use private data for its own use.
<!--  CEP: This sentence does not seem helpful.  -->
                                                           The private
   data immediately follows the last field in the GUE header and is not
   a fixed length. This data is considered part of the GUE header and
   MUST be accounted for in header length (Hlen). The length of the
   private data MUST be a multiple of four and is determined by
   subtracting the offset of private data in the GUE header from the
   header length. Specifically:

      Private_length = (Hlen * 4) - Length(extensions)

   where "Length(extensions)" returns the sum of lengths of all the extension
   fields following the GUE header. When there is no private data
   present, the length of the private data is zero.

   The semantics and interpretation of private data are implementation
   specific. An encapsulator and decapsulator MUST agree on the meaning of
   private data before using it. The mechanism to achieve this agreement is
   outside the scope of this document.

   If a decapsulator receives a GUE packet with private data, it MUST
   validate the private data. If a decapsulator does not
   expect private data from an encapsulator, the packet MUST be dropped.
   If a decapsulator cannot validate the contents of private data per
 


Herbert, Yong, Zia        Expires March, 2019                  [Page 12]

Internet Draft         Generic UDP Encapsulation         August 31, 2018


   the provided semantics, the packet MUST also be dropped.
<!--  CEP: since the structure of the private data is out of scope,
           the following RFC 2119 language is used incorrectly.
                                                            An
   implementation MAY place security data in GUE private data which if
   present MUST be verified for packet acceptance.              -->

3.5. Message types

3.5.1. Control messages

   Control messages carry formatted data that are implicitly addressed
   to the decapsulator to monitor or control the state or behavior of a
   tunnel.  For instance, an echo request and corresponding echo
   reply message can be defined to test for liveness.

   Control messages are present in the GUE header when the C-bit is
   set. The payload is interpreted as a control message with type
   specified in the proto/ctype field. The format and contents of the
   control message are indicated by the type and can be variable length.

   Other than interpreting the proto/ctype field as a control message
   type, the meaning and semantics of the rest of the elements in the
   GUE header are the same as that of data messages. Forwarding and
   routing of control messages should be the same as that of a data
   message with the same outer IP and UDP header and GUE flags; this
   ensures that control messages can be created that follow the same
   path as data messages.

3.5.2. Data messages

   Data messages carry encapsulated packets that are addressed to the
   protocol stack for the associated protocol. Data messages are a
   primary means of encapsulation and can be used to create tunnels for
   overlay networks.

   Data messages are indicated in GUE header when the C-bit is not set.
   The payload of a data message is interpreted as an encapsulated
   packet of an Internet protocol indicated in the proto/ctype field.
   The packet immediately follows the GUE header.

3.6. Hiding the transport layer protocol number

   The GUE header indicates the Internet protocol of the encapsulated
   packet. A protocol number is either contained in the Proto/ctype
   field of the primary GUE header or in the Payload Type field of a GUE
   Transform extension field (used to encrypt the payload with DTLS,
   [GUEEXTEN]). If the transport protocol number needs to be hidden from
   the network, then a trivial destination options can be used, as
   specified below.
<!--   CEP: This destination option needs to be specified in this document.-->

   The PadN destination option [RFC2460] can be used to encode the
 <!--  CEP: PadN is not a destination option. -->


Herbert, Yong, Zia        Expires March, 2019                  [Page 13]

Internet Draft         Generic UDP Encapsulation         August 31, 2018


   transport protocol as a next header of an extension header (and
   maintain alignment of encapsulated transport header). The
   Proto/ctype field or Payload Type field of the GUE Transform field is
   set to 60 to indicate that the first encapsulated header is a
   destination options extension header.

   The format of the extension header is below:

      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Next Header |    2      |     1     |      0    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   For IPv4, it is permitted in GUE to used this precise destination
   option to hide the protocol number. In this case next
   header MUST refer to a valid IP protocol for IPv4. No other extension
   headers or destination options are permitted with IPv4.
































 


Herbert, Yong, Zia        Expires March, 2019                  [Page 14]

Internet Draft         Generic UDP Encapsulation         August 31, 2018


4. Variant 1

   Variant 1 of GUE allows direct encapsulation of IPv4 and IPv6 in UDP.
   In this variant there is no GUE header; a UDP packet carries an IP
   packet. The first two bits of the UDP payload for GUE are the GUE
   variant and coincide with the first two bits of the version number in
   the IP header. The first two version bits of IPv4 and IPv6 are 01, so
   we use GUE variant 1 for direct IP encapsulation which makes two bits
   of GUE variant to also be 01.

   This technique is effectively a means to compress out the version 0
   GUE header when encapsulating IPv4 or IPv6 packets and there are no
   flags or extension fields present. This method is compatible to use
   on the same port number as packets with the GUE header (GUE variant 0
   packets). This technique saves encapsulation overhead on costly links
   for the common use of IP encapsulation, and also obviates the need to
   allocate a separate port number for IP-over-UDP encapsulation.

4.1. Direct encapsulation of IPv4

   The format for encapsulating IPv4 directly in UDP is:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+\
   |        Source port            |      Destination port         | |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ UDP
   |           Length              |          Checksum             | |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+/
   |0|1|0|0|  IHL  |Type of Service|          Total Length         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Identification        |Flags|      Fragment Offset    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Time to Live |   Protocol    |   Header Checksum             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Source IPv4 Address                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Destination IPv4 Address                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The UDP fields are set in a similar manner as described in section
   3.1.

   Note that the 0100 value in the first four bits of the the UDP
   payload expresses the GUE variant as 1 (bits 01) and IP version as 4
   (bits 0100).


 


Herbert, Yong, Zia        Expires March, 2019                  [Page 15]

Internet Draft         Generic UDP Encapsulation         August 31, 2018


4.2. Direct encapsulation of IPv6

   The format for encapsulating IPv6 directly in UDP is demonstrated
   below:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+\
   |        Source port            |      Destination port         | |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ UDP
   |           Length              |          Checksum             | |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+/
   |0|1|1|0| Traffic Class |           Flow Label                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |         Payload Length        |     NextHdr   |   Hop Limit   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                                                               +
   |                                                               |
   +                        Source IPv6 Address                    +
   |                                                               |
   +                                                               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                                                               +
   |                                                               |
   +                      Destination IPv6 Address                 +
   |                                                               |
   +                                                               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The UDP fields are set in a similar manner as described in section
   3.1.

   Note that the 0110 value in the first four bits of the the UDP
   payload expresses the GUE variant as 1 (bits 01) and IP version as 6
   (bits 0110).









 


Herbert, Yong, Zia        Expires March, 2019                  [Page 16]

Internet Draft         Generic UDP Encapsulation         August 31, 2018


5. Operation

   The figure below illustrates the use of GUE encapsulation between two
   hosts. Host 1 is sending packets to Host 2. An encapsulator performs
   encapsulation of packets from Host 1. These encapsulated packets
   traverse the network as UDP packets. At the decapsulator, packets are
   decapsulated and sent on to Host 2. Packet flow in the reverse
   direction need not be symmetric; for example, the reverse path might
   not use GUE and/or any other form of encapsulation.

   +---------------+                       +---------------+
   |               |                       |               |
   |    Host 1     |                       |     Host 2    |
   |               |                       |               |
   +---------------+                       +---------------+
          |                                        ^
          V                                        |
   +---------------+   +---------------+   +---------------+
   |               |   |               |   |               |
   | Encapsulator  |-->|    Layer 3    |-->| Decapsulator  |
   |               |   |    Network    |   |               |
   +---------------+   +---------------+   +---------------+
<!--  CEP: This is true for any L3 encapsulation -->
<!--  CEP: This figure illustrates something that is most likely
           obvious to almost all readers.  -->

   The encapsulator and decapsulator may be co-resident with the
   corresponding hosts, or may be on separate nodes in the network.

5.1. Network tunnel encapsulation

   Network tunneling can be achieved by encapsulating layer 2 or layer 3
   packets. In this case the encapsulator and decapsulator nodes are the
   tunnel endpoints. These could be routers that provide network tunnels
   on behalf of communicating hosts.
<!--  CEP: Do you mean that GUE can encapsulate L2 frames?  If so, this
           contradicts earlier text in several places. --->

5.2. Transport layer encapsulation

   When encapsulating layer 4 packets, the encapsulator and decapsulator
   should be co-resident with the hosts.
<!--  CEP: This seems to try to distinguish between "layer 4" and
           IP protocol number.  If so, what is the distinction??  -->
                                        In this case, the encapsulation
   headers are inserted between the IP header and the transport packet.
   The addresses in the IP header refer to both the endpoints of the
   encapsulation and the endpoints for terminating the transport
   protocol. Note that the transport layer ports in the encapsulated
   packet are independent of the UDP ports in the outer packet.

   Details about performing transport layer encapsulation are discussed
   in [TOU].
<!--  CEP: I think those details belong here.  If not, this is a normative
           dependency on a non-WG document that is not yet mature. -->


 


Herbert, Yong, Zia        Expires March, 2019                  [Page 17]

Internet Draft         Generic UDP Encapsulation         August 31, 2018


5.3. Encapsulator operation

   Encapsulators create GUE data messages, set the fields of the UDP
   header, set flags and optional extension fields in the GUE header,
   and forward packets to a decapsulator.
<!--  CEP: According to the figure, encapsulators don't have to
           create data.  Moreover, the whole point of "generic"
           encapsulation seems to be independence from content. -->

   An encapsulator can be an end host originating the packets of a flow,
   or can be a network device performing encapsulation on behalf of
   hosts (routers implementing tunnels for instance). In either case,
   the intended target (decapsulator) is indicated by the outer
   destination IP address and destination port in the UDP header.

   If an encapsulator is tunneling packets -- that is encapsulating
   packets of layer 3 protocols (e.g. EtherIP, IPIP, ESP
   tunnel mode) -- it MUST follow standard conventions for tunneling
   of one protocol over another. For instance, if an IP packet is being
   encapsulated in GUE then diffserv interaction [RFC2983] and ECN
   propagation for tunnels [RFC6040] MUST be followed.
<!--  CEP: this violates "generic" unless all IP protocols are
           respected in that way.  -->
<!--  CEP: GUE states several times that implementations MUST follow
           standards.  Does that mean that sometimes implementations
           MAY break standards if not explicitly required to follow
           them?  I hope not!  I think it would be better to avoid
           recommendations about following existing standards. -->

5.4. Decapsulator operation

   A decapsulator performs decapsulation of GUE packets. A decapsulator
   is addressed by the outer destination IP address of a GUE packet. 
   The decapsulator validates packets, including fields of the GUE
   header.

   If a decapsulator receives a GUE packet with an unsupported variant,
   unknown flag, bad header length (too small for included extension
   fields), unknown control message type, bad protocol number, an
   unsupported payload type, or an otherwise malformed header, it MUST
   drop the packet. Such events MAY be logged subject to configuration
   and rate limiting of logging messages. Note that set flags in a GUE
   header that are unknown to a decapsulator MUST NOT be ignored. If a
   GUE packet is received by a decapsulator with unknown flags, the
   packet MUST be dropped.
<!--  CEP: An ICMP message seems appropriate here.  -->

5.4.1. Processing a received data message

   If a valid data message is received, the UDP header and GUE header
<!--  CEP: Need to define "valid".  -->
   are removed from the packet. The outer IP header remains intact and
   the next protocol in the IP header is set to the protocol from the
   proto field in the GUE header. The resulting packet is then
   resubmitted into the protocol stack to process that packet as though
   it was received with the protocol in the GUE header.

   As an example, consider that a data message is received where GUE
   encapsulates an IPv4 packet using GUE variant 0. In this case proto
   field in the GUE header is set to 4 for IPv4 encapsulation:
 


Herbert, Yong, Zia        Expires March, 2019                  [Page 18]

Internet Draft         Generic UDP Encapsulation         August 31, 2018


   +-------------------------------------+
   |   IP header (next proto = 17,UDP)   |
   |-------------------------------------|
   |                  UDP                |
   |-------------------------------------|
   |  GUE (proto = 4,IPv4 encapsulation) |
   |-------------------------------------|
   |        IPv4 header and packet       |
   +-------------------------------------+
<!--  CEP: All figures should have figure numbers, even if not
           cross-referenced in this document. -->

   The receiver removes the UDP and GUE headers and sets the next
   protocol field in the IP packet to 4, which is derived from the GUE
   proto field. The resultant packet would have the format:

   +-------------------------------------+
   |   IP header (next proto = 4,IPv4)   |
   |-------------------------------------|
   |         IP header and packet        |
   +-------------------------------------+

   This packet is then resubmitted into the protocol stack to be
   processed as an IPv4 encapsulated packet.

5.4.2. Processing a received control message

   If a valid control message is received, the packet MUST be processed
   as a control message.
<!--  CEP: Need to define "valid".  What exactly is meant by "processed
           as a control message"?  In each case, the processing is
           determined by the GUE header fields.   -->
                         The specific processing to be performed depends
   on the value in the ctype field of the GUE header.

5.5. Router and switch operation

   Routers and switches MUST forward GUE packets as standard UDP/IP
   packets.
<!--  CEP: Another puzzling unenforceable mandate.  Why would
           inclusion of GUE suddenly invalidate previous standards? -->
             The outer five-tuple should contain sufficient information
   to perform flow classification corresponding to the flow of the inner
   packet. A router does not normally need to parse a GUE header, and
   none of the flags or extension fields in the GUE header are expected
   to affect routing. In cases where the outer five-tuple does not
   provide sufficient entropy for flow classification, for instance UDP
   ports are fixed to provide connection semantics (section 5.6.1), then
   the encapsulated packet MAY be parsed to determine flow entropy.

   A router MUST NOT modify a GUE header when forwarding a packet. It
   MAY encapsulate a GUE packet in another GUE packet, for instance to
   implement a network tunnel (i.e. by encapsulating an IP packet with a
   GUE payload in another IP packet as a GUE payload). In this case, the
   router takes the role of an encapsulator, and the corresponding
   decapsulator is the logical endpoint of the tunnel. When
   encapsulating a GUE packet within another GUE packet, there are no
 


Herbert, Yong, Zia        Expires March, 2019                  [Page 19]

Internet Draft         Generic UDP Encapsulation         August 31, 2018


   provisions to automatically copy flags or fields to the outer GUE
   header. Each layer of encapsulation is considered independent.
<!--  CEP: Does this document intend to update RFC 2983, 6040?  -->

5.6. Middlebox interactions

   A middlebox MAY interpret some flags and extension fields of the GUE
   header for classification purposes, but is not required to understand
   any of the flags or extension fields in GUE packets. A middlebox MUST
   NOT drop a GUE packet merely because there are flags unknown to it.
<!--  CEP: unenforceable.  -->
   The header length in the GUE header allows a middlebox to inspect the
   payload packet without needing to parse the flags or extension
   fields.

5.6.1. Inferring connection semantics

   A middlebox might infer bidirectional connection semantics for a UDP
   flow. For instance, a stateful firewall might create a five-tuple
   rule to match flows on egress, and a corresponding five-tuple rule
   for matching ingress packets where the roles of source and
   destination are reversed for the IP addresses and UDP port numbers.
   To operate in this environment, a GUE tunnel should be configured to
   assume connected semantics defined by the UDP five tuple and the use
   of GUE encapsulation needs to be symmetric between both endpoints.
   The source port set in the UDP header MUST be the destination port
   the peer would set for replies. In this case, the UDP source port for
   a tunnel would be a fixed value and not set to be flow entropy as
   described in section 5.11.

   The selection of whether to make the UDP source port fixed or set to
   a flow entropy value for each packet sent SHOULD be configurable for
   a tunnel.
<!--  CEP: The SHOULD is a mandate on the configuration of GUE, not
           on GUE protocol.  -->
             The default MUST be to set the flow entropy value in the
   UDP source port.

5.6.2. NAT

   IP address and port translation can be performed on the UDP/IP
   headers adhering to the requirements for NAT with UDP [RFC4787]. In
   the case of stateful NAT, connection semantics MUST be applied to a
   GUE tunnel as described in section 5.6.1. GUE endpoints MAY also
   invoke STUN [RFC5389] or ICE [RFC5245] to manage NAT port mappings
   for encapsulations.

5.7. Checksum Handling

   The potential for mis-delivery of packets due to corruption of IP,
   UDP, or GUE headers needs to be considered. Historically, the UDP
   checksum would be considered sufficient as a check against corruption
   of either the UDP header and payload or the IP addresses.
 


Herbert, Yong, Zia        Expires March, 2019                  [Page 20]

Internet Draft         Generic UDP Encapsulation         August 31, 2018


   Encapsulation protocols, such as GUE, can be originated or terminated
   on devices incapable of computing the UDP checksum for packet.
<!--  CEP: citation needed for such devices.  -->
                                                                   This
   section discusses the requirements around checksum and alternatives
   that might be used when an endpoint does not support UDP checksum.

5.7.1. Requirements

   One of the following requirements MUST be met:
<!--  CEP: This is a tautology.  Either the checksum is zero, or not. -->

  o UDP checksums are enabled (for IPv4 or IPv6).
<!--  CEP: Is GUE defined in this document for anything other
           than IPv[4,6]?  Is UDP defined for anything else??  -->

  o The GUE header checksum is used (defined in [GUEEXTEN]).

  o Use zero UDP checksums. This is always permissible with IPv4; in
    IPv6, they can only be used in accordance with applicable
    requirements in [RFC8086], [RFC6935], and [RFC6936].

5.7.2. UDP Checksum with IPv4

    For UDP in IPv4, the UDP checksum MUST be processed as specified in
    [RFC768] and [RFC1122] for both transmit and receive. An
    encapsulator MAY set the UDP checksum to zero for performance or
    implementation considerations. The IPv4 header includes a checksum
    that protects against mis-delivery of the packet due to corruption
    of IP addresses. The UDP checksum potentially provides protection
    against corruption of the UDP header, GUE header, and GUE payload.
    Enabling or disabling the use of checksums is a deployment
    consideration that SHOULD take into account the risk and effects of
    packet corruption, and whether the packets in the network are
    already adequately protected by other, possibly stronger mechanisms,
    such as the Ethernet CRC. If an encapsulator sets a zero UDP
    checksum for IPv4, it SHOULD use the GUE header checksum as
    described in [GUEEXTEN] assuming there are no other mechanisms used
    to protect the GUE packet.
<!--  CEP: This last sentence seems to disregard the previous sentence,
           which would then obviate the need for a GUE checksum.  -->

    When a decapsulator receives a packet, the UDP checksum field MUST
    be processed. If the UDP checksum is non-zero, the decapsulator MUST
    verify the checksum before accepting the packet. By default, a
    decapsulator SHOULD accept UDP packets with a zero checksum. A node
    MAY be configured to disallow zero checksums per [RFC1122].
    Configuration of zero checksums can be selective. For instance, zero
    checksums might be disallowed from certain hosts that are known to
    be traversing paths subject to packet corruption. If verification of
    a non-zero checksum fails, a decapsulator lacks the capability to
    verify a non-zero checksum, or a packet with a zero-checksum was
    received and the decapsulator is configured to disallow, then the
    packet MUST be dropped.

 


Herbert, Yong, Zia        Expires March, 2019                  [Page 21]

Internet Draft         Generic UDP Encapsulation         August 31, 2018


5.7.3. UDP Checksum with IPv6

    In IPv6, there is no checksum in the IPv6 header that protects
    against mis-delivery due to address corruption. Therefore, when GUE
    is used over IPv6, either the UDP checksum or the GUE header
    checksum SHOULD be used unless there are alternative mechanisms in
    use that protect against misdelivery. The UDP checksum and GUE
    header checksum SHOULD NOT be used at the same time since that would
    be mostly redundant.
<!--  CEP: Why not simply mandate the UDP checksum?  -->

    If neither the UDP checksum or the GUE header checksum is used, then
    the requirements for using zero IPv6 UDP checksums in [RFC6935] and
    [RFC6936] MUST be met.

    When a decapsulator receives a packet, the UDP checksum field MUST
    be processed. If the UDP checksum is non-zero, the decapsulator MUST
    verify the checksum before accepting the packet. By default a
    decapsulator MUST only accept UDP packets with a zero checksum if
    the GUE header checksum is used and is verified. If verification of
    a non-zero checksum fails, a decapsulator lacks the capability to
    verify a non-zero checksum, or a packet with a zero-checksum and no
    GUE header checksum was received, the packet MUST be dropped.

5.8. MTU and fragmentation

    Standard conventions for handling of MTU (Maximum Transmission Unit)
    and fragmentation in conjunction with networking tunnels
    (encapsulation of layer 2 or layer 3 packets) MUST be followed.
    Details are described in MTU and Fragmentation Issues with In-the-
    Network Tunneling [RFC4459].

    If a packet is fragmented before encapsulation in GUE, all the
    related fragments MUST be encapsulated using the same UDP source
    port. An operator SHOULD set MTU to account for encapsulation
    overhead and reduce the likelihood of fragmentation.

    Alternative to IP fragmentation, the GUE fragmentation extension can
    be used. GUE fragmentation is described in [GUEEXTEN].
<!--  CEP: GUE fragmentation has to be specified in this document. -->

5.9. Congestion control

    Per requirements of [RFC5405], if the IP traffic encapsulated with
    GUE implements proper congestion control no additional mechanisms
    are required.

    In the case that the encapsulated traffic does not implement any or
    sufficient control, or it is not known whether a transmitter will
    consistently implement proper congestion control, then congestion
 


Herbert, Yong, Zia        Expires March, 2019                  [Page 22]

Internet Draft         Generic UDP Encapsulation         August 31, 2018


    control at the encapsulation layer MUST be provided per [RFC5405].
    This applies to a significant use case in network
    virtualization in which guests run third party networking stacks
    that cannot be implicitly trusted to implement conformant congestion
    control.

    Out of band mechanisms such as rate limiting, Managed Circuit
    Breaker [RFC8084], or traffic isolation MAY be used to provide
    rudimentary congestion control. For finer-grained congestion control
    that allows alternate congestion control algorithms, reaction time
    within an RTT, and interaction with ECN, in-band mechanisms might be
    warranted.

5.10. Multicast

    GUE packets can be multicast to decapsulators using a multicast
    destination address in the encapsulating IP headers. Each receiving
    host will decapsulate the packet independently following normal
    decapsulator operations. The receiving decapsulators need to agree
    on the same set of GUE parameters and properties; how such an
    agreement is reached is outside the scope of this document.

    GUE allows encapsulation of unicast, broadcast, or multicast
    traffic. Flow entropy (the value in the UDP source port) can be
    generated from the header of encapsulated unicast or
    broadcast/multicast packets at an encapsulator. The mapping
    mechanism between the encapsulated multicast traffic and the
    multicast capability in the IP network is transparent and
    independent of the encapsulation and is otherwise outside the scope
    of this document.

5.11. Flow entropy for ECMP

5.11.1. Flow classification

    A major objective of using GUE is that a network device can perform
    flow classification corresponding to the flow of the inner
    encapsulated packet based on the contents in the outer headers.
<!--  CEP: This sentence belongs in the Introduction.  -->

    Hardware devices commonly perform hash computations on packet
    headers to classify packets into flows or flow buckets. Flow
    classification is done to support load balancing of flows across a
    set of networking resources. Examples of such load balancing
    techniques are Equal Cost Multipath routing (ECMP), port selection
    in Link Aggregation, and NIC device Receive Side Scaling (RSS). 
<!--  CEP: citations needed.  -->
    Hashes are usually either a three-tuple hash of IP protocol, source
    address, and destination address; or a five-tuple hash consisting of
    IP protocol, source address, destination address, source port, and
 


Herbert, Yong, Zia        Expires March, 2019                  [Page 23]

Internet Draft         Generic UDP Encapsulation         August 31, 2018


    destination port. Typically, networking hardware will compute five-
    tuple hashes for TCP and UDP, but only three-tuple hashes for other
    IP protocols. Since the five-tuple hash provides more granularity,
    load balancing can be finer-grained with better distribution. When a
    packet is encapsulated with GUE and connection semantics are not
    applied, the source port in the outer UDP packet is set to a flow
    entropy value that corresponds to the flow of the inner packet. When
    a device computes a five-tuple hash on the outer UDP/IP header of a
    GUE packet, the resultant value classifies the packet per its inner
    flow.

    Examples of deriving flow entropy for encapsulation are:

      o If the encapsulated packet is a layer 4 packet, TCPv4 for
        instance, the flow entropy could be based on the canonical five-
        tuple hash of the inner packet.

      o If the encapsulated packet is an AH transport mode packet with
        TCP as next header, the flow entropy could be a hash over a
        three-tuple: TCP protocol and TCP ports of the encapsulated
        packet.

      o If a node is encrypting a packet using ESP tunnel mode and GUE
        encapsulation, the flow entropy could be based on the contents
        of the clear-text packet. For instance, a canonical five-tuple
        hash for a TCP/IP packet could be used.

   [RFC6438] discusses methods to compute and set flow entropy value for
   IPv6 flow labels. Such methods can also be used to create flow
   entropy values for GUE.
<!--  CEP: for interoperability, maybe more specifics are needed. -->

5.11.2. Flow entropy properties

   The flow entropy is the value set in the UDP source port of a GUE
   packet. Flow entropy in the UDP source port SHOULD adhere to the
   following properties:

      o The value set in the source port is within the ephemeral port
        range (49152 to 65535 [RFC6335]). Since the high order two bits
        of the port are set to one, this provides fourteen bits of
        entropy for the value.

      o The flow entropy has a uniform distribution across encapsulated
        flows.

      o An encapsulator MAY occasionally change the flow entropy used
        for an inner flow (for security, route
        selection, etc). To avoid thrashing or flapping the value, the
 


Herbert, Yong, Zia        Expires March, 2019                  [Page 24]

Internet Draft         Generic UDP Encapsulation         August 31, 2018


        flow entropy used for a flow SHOULD NOT change more than once
        every thirty seconds (or a configurable value).
<!--  CEP: This configurable value needs a name. -->

      o Decapsulators, or any networking devices, SHOULD NOT attempt to
        interpret flow entropy as anything more than an opaque value.
        Neither should they attempt to reproduce the hash calculation
        used by an encapasulator in creating a flow entropy value. They
        MAY use the value to match further receive packets for steering
        decisions, but MUST NOT assume that the hash uniquely or
        permanently identifies a flow. 

      o Input to the flow entropy calculation is not restricted to ports
        and addresses; input could include flow label from an IPv6
        packet, SPI from an ESP packet, or other flow related state in
        the encapsulator that is not necessarily conveyed in the packet.

      o The assignment function for flow entropy SHOULD be randomly
        seeded to mitigate denial of service attacks. The seed SHOULD be
        changed periodically.
<!--  CEP: This needs to be specified. -->

5.12 Negotiation of acceptable flags and extension fields

   An encapsulator and decapsulator need to achieve agreement about GUE
   parameters that will be used in communications. Parameters include
   supported GUE variants, flags and extension fields that can be used,
   security algorithms and keys, supported protocols and control
   messages, etc. This document proposes different general methods to
   accomplish this, however the details of implementing these are
   considered out of scope.

   General methods for this are:

      o Configuration. The parameters used for a tunnel are configured
        at each endpoint.

      o Negotiation. A tunnel negotiation can be performed. This could
        be accomplished in-band of GUE using control messages or private
        data.

      o Via a control plane. Parameters for communicating with a tunnel
        endpoint can be set in a control plane protocol (such as that
        needed for network virtualization).

      o Via security negotiation. Use of security typically implies a
        key exchange between endpoints. Other GUE parameters may be
        conveyed as part of that process.


 


Herbert, Yong, Zia        Expires March, 2019                  [Page 25]

Internet Draft         Generic UDP Encapsulation         August 31, 2018


6. Motivation for GUE

   This section presents the motivation for GUE with respect to other
   encapsulation methods.
<!--  CEP: This section needs to be moved much closer to the beginning
           of the document, perhaps just before Terminology.  -->

6.1. Benefits of GUE

      * GUE is a generic encapsulation protocol. GUE can encapsulate
        protocols that are represented by an IP protocol number.

      * GUE is an extensible encapsulation protocol. Standardized
        optional data such as security, virtual networking identifiers,
        fragmentation are being defined.
<!--  CEP: citations requested.  -->

      * For extensibility, GUE uses flag fields as opposed to TLVs as
        some other encapsulation protocols do. Flag fields are strictly
        ordered, allow random access, and are efficient in use of header
        space.

      * GUE allows private data to be sent as part of the encapsulation.
        This permits experimentation or customization in deployment.

      * GUE allows sending of control messages such as OAM using the
        same GUE header format (for routing purposes) as normal data
        messages.

      * GUE maximizes deliverability of non-UDP and non-TCP protocols.
<!--  CEP: This claim relies on the assumption the intermediate
           routing points are happy with random UDP payloads. -->

      * GUE provides a means for exposing per flow entropy for ECMP for
        atypical protocols such as SCTP, DCCP, ESP, etc.

6.2 Comparison of GUE to other encapsulations
<!--  CEP: This section also belongs much earlier in the document. -->

   A number of different encapsulation techniques have been proposed for
   the encapsulation of one protocol over another. EtherIP [RFC3378]
   provides tunneling of Ethernet frames over IP. GRE [RFC2784],
   MPLS [RFC4023], and L2TP [RFC2661] provide methods for tunneling
   layer 2 and layer 3 packets over IP. NVGRE [RFC7637] and VXLAN
   [RFC7348] are proposals for encapsulation of layer 2 packets for
   network virtualization. IPIP [RFC2003] and Generic packet tunneling
   in IPv6 [RFC2473] provide methods for tunneling IP packets over IP. 

   Several proposals exist for encapsulating packets over UDP including
   ESP over UDP [RFC3948], TCP directly over UDP [TCPUDP], VXLAN
   [RFC7348], LISP [RFC6830] which encapsulates layer 3 packets,
   MPLS/UDP [RFC7510], GENEVE [GENEVE], and GRE-in-UDP Encapsulation
   [RFC8086].
 


Herbert, Yong, Zia        Expires March, 2019                  [Page 26]

Internet Draft         Generic UDP Encapsulation         August 31, 2018


   GUE has the following discriminating features:

      o UDP encapsulation leverages specialized network device
        processing for efficient transport. The semantics for using the
        UDP source port for flow entropy as input to ECMP are defined in
        section 5.11.

      o GUE permits encapsulation of arbitrary IP protocols.

      o Multiple protocols can be multiplexed over a single UDP port
        number. This is in contrast to techniques to encapsulate
        protocols over UDP using a protocol specific port number (such
        as ESP/UDP, GRE/UDP, SCTP/UDP). GUE provides a uniform and
        extensible mechanism for encapsulating all IP protocols in UDP
        with minimal overhead (as few as four bytes of additional header).

      o GUE is extensible. New flags and extension fields can be
        defined.

      o The GUE header includes a header length field. This allows a
        network node to inspect an encapsulated packet without needing
        to parse the full encapsulation header.

      o Private data in the encapsulation header allows local
        customization and experimentation while being compatible with
        processing in network nodes (routers and middleboxes).

      o GUE includes both data messages (encapsulation of packets) and
        control messages (such as OAM).

      o The flags-field model facilitates efficient implementation of
        extensibility in hardware. For instance, a TCAM can be used to
        parse a known set of N flags where the number of entries in the
        TCAM is 2^N. By comparison, the number of TCAM entries needed to
        parse a set of N arbitrarily ordered TLVS is approximately e*N!.

      o GUE includes a variant that encapsulates IPv4 and IPv6 packets
        directly within UDP. 









 


Herbert, Yong, Zia        Expires March, 2019                  [Page 27]

Internet Draft         Generic UDP Encapsulation         August 31, 2018


7. Security Considerations

   There are two important considerations of security with respect to
   GUE.

      o Authentication and integrity of the GUE header.

      o Authentication, integrity, and confidentiality of the GUE
        payload.

   GUE security is provided by extensions for security defined in
   [GUEEXTEN]. These extensions include methods to authenticate the GUE
   header and encrypt the GUE payload.
<!--  CEP: Please explain why GUE requires yet another mechanism.  -->

   The GUE header can be authenticated using a security extension for an
   HMAC. Securing the GUE payload can be accomplished use of the GUE
   Payload Transform. This extension can be used to perform DTLS in the
   payload of a GUE packet to encrypt the payload.

   A hash function for computing flow entropy (section 5.11) SHOULD be
   randomly seeded to mitigate some possible denial service attacks.
<!--  CEP: Citation needed for "possible" and for how a random seed
           deters them.  -->

8. IANA Considerations

8.1. UDP source port

   A user UDP port number assignment for GUE has been assigned:

          Service Name: gue
          Transport Protocol(s): UDP
          Assignee: Tom Herbert <tom@xxxxxxxxxxxxxxx>
          Contact: Tom Herbert <tom@xxxxxxxxxxxxxxx>
          Description: Generic UDP Encapsulation
          Reference: draft-herbert-gue
          Port Number: 6080
          Service Code: N/A
          Known Unauthorized Uses: N/A
          Assignment Notes: N/A










 


Herbert, Yong, Zia        Expires March, 2019                  [Page 28]

Internet Draft         Generic UDP Encapsulation         August 31, 2018


8.2. GUE variant number

   IANA is requested to set up a registry for the GUE variant number.
   The GUE variant number is 2 bits containing four possible values.
   This document defines version 0 and 1. New values are assigned in
   accordance with RFC Required policy [RFC5226].

      +----------------+----------------+---------------+
      | Variant number | Description    | Reference     |
      +----------------+----------------+---------------+
      | 0              | GUE Version 0  | This document |
      |                | with header    |               |
      |                |                |               |
      | 1              | GUE Version 0  | This document |
      |                | with direct IP |               |
      |                | encapsulation  |               |
      |                |                |               |
      | 2..3           | Unassigned     |               |
      +----------------+----------------+---------------+

8.3. Control types

   IANA is requested to set up a registry for the GUE control types.
   Control types are 8 bit values.  New values for control types 1-127
   are assigned in accordance with RFC Required policy [RFC5226].

      +----------------+------------------+---------------+
      |  Control type  | Description      | Reference     |
      +----------------+------------------+---------------+
      | 0              | Control payload  | This document |
      |                |  needs more      |               |
      |                |  context for     |               |
      |                |  interpretation  |               |
      |                |                  |               |
      | 1..127         | Unassigned       |               |
      |                |                  |               |
      | 128..255       | User defined     | This document |
      +----------------+------------------+---------------+

9. Acknowledgements

   The authors would like to thank David Liu, Erik Nordmark, Fred
   Templin, Adrian Farrel, Bob Briscoe, and Murray Kucherawy for
   valuable input on this draft.




 


Herbert, Yong, Zia        Expires March, 2019                  [Page 29]

Internet Draft         Generic UDP Encapsulation         August 31, 2018


10. References

10.1. Normative References


   [RFC0768]  Postel, J., "User Datagram Protocol", STD 6, RFC 768, DOI
              10.17487/RFC0768, August 1980, <http://www.rfc-
              editor.org/info/rfc768>.

   [RFC1122]  Braden, R., Ed., "Requirements for Internet Hosts -
              Communication Layers", STD 3, RFC 1122, DOI
              10.17487/RFC1122, October 1989, <http://www.rfc-
              editor.org/info/rfc1122>.

   [RFC2434]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", RFC 2434, DOI
              10.17487/RFC2434, October 1998, <http://www.rfc-
              editor.org/info/rfc2434>.

   [RFC2983]  Black, D., "Differentiated Services and Tunnels", RFC
              2983, DOI 10.17487/RFC2983, October 2000, <http://www.rfc-
              editor.org/info/rfc2983>.

   [RFC6040]  Briscoe, B., "Tunnelling of Explicit Congestion
              Notification", RFC 6040, DOI 10.17487/RFC6040, November
              2010, <http://www.rfc-editor.org/info/rfc6040>.

   [RFC6935]  Eubanks, M., Chimento, P., and M. Westerlund, "IPv6 and
              UDP Checksums for Tunneled Packets", RFC 6935, DOI
              10.17487/RFC6935, April 2013, <http://www.rfc-
              editor.org/info/rfc6935>.

   [RFC6936]  Fairhurst, G. and M. Westerlund, "Applicability Statement
              for the Use of IPv6 UDP Datagrams with Zero Checksums",
              RFC 6936, DOI 10.17487/RFC6936, April 2013,
              <http://www.rfc-editor.org/info/rfc6936>.

   [RFC4459]  Savola, P., "MTU and Fragmentation Issues with In-the-
              Network Tunneling", RFC 4459, DOI 10.17487/RFC4459, April
              2006, <http://www.rfc-editor.org/info/rfc4459>.

10.2. Informative References

   [RFC3828]  Larzon, L-A., Degermark, M., Pink, S., Jonsson, L-E., Ed.,
              and G. Fairhurst, Ed., "The Lightweight User Datagram
              Protocol (UDP-Lite)", RFC 3828, July 2004,
              <http://www.rfc-editor.org/info/rfc3828>.

 


Herbert, Yong, Zia        Expires March, 2019                  [Page 30]

Internet Draft         Generic UDP Encapsulation         August 31, 2018


   [RFC7348]  Mahalingam, M., Dutt, D., Duda, K., Agarwal, P., Kreeger,
              L., Sridhar, T., Bursell, M., and C. Wright, "Virtual
              eXtensible Local Area Network (VXLAN): A Framework for
              Overlaying Virtualized Layer 2 Networks over Layer 3
              Networks", RFC 7348, August 2014, <http://www.rfc-
              editor.org/info/rfc7348>.

   [RFC7605]  Touch, J., "Recommendations on Using Assigned Transport
              Port Numbers", BCP 165, RFC 7605, DOI 10.17487/RFC7605,
              August 2015, <http://www.rfc-editor.org/info/rfc7605>.

   [RFC7637]  Garg, P., Ed., and Y. Wang, Ed., "NVGRE: Network
              Virtualization Using Generic Routing Encapsulation", RFC
              7637, DOI 10.17487/RFC7637, September 2015,
              <http://www.rfc-editor.org/info/rfc7637>.

   [RFC8086]  Yong, L., Ed., Crabbe, E., Xu, X., and T. Herbert, "GRE-
              in-UDP Encapsulation", RFC 8086, DOI 10.17487/RFC8086,
              March 2017, <http://www.rfc-editor.org/info/rfc8086>.

   [RFC7510]  Xu, X., Sheth, N., Yong, L., Callon, R., and D. Black,
              "Encapsulating MPLS in UDP", RFC 7510, DOI
              10.17487/RFC7510, April 2015, <http://www.rfc-
              editor.org/info/rfc7510>.

   [RFC4340]  Kohler, E., Handley, M., and S. Floyd, "Datagram
              Congestion Control Protocol (DCCP)", RFC 4340, DOI
              10.17487/RFC4340, March 2006, <http://www.rfc-
              editor.org/info/rfc4340>.

   [RFC4787]  Audet, F., Ed., and C. Jennings, "Network Address
              Translation (NAT) Behavioral Requirements for Unicast
              UDP", BCP 127, RFC 4787, DOI 10.17487/RFC4787, January
              2007, <http://www.rfc-editor.org/info/rfc4787>.

   [RFC5389]  Rosenberg, J., Mahy, R., Matthews, P., and D. Wing,
              "Session Traversal Utilities for NAT (STUN)", RFC 5389,
              DOI 10.17487/RFC5389, October 2008, <http://www.rfc-
              editor.org/info/rfc5389>.

   [RFC5285]  Rosenberg, J., "Interactive Connectivity Establishment
              (ICE): A Protocol for Network Address Translator (NAT)
              Traversal for Offer/Answer Protocols", RFC 5245, DOI
              10.17487/RFC5245, April 2010, <http://www.rfc-
              editor.org/info/rfc5245>.

   [RFC5405]  Eggert, L. and G. Fairhurst, "Unicast UDP Usage Guidelines
              for Application Designers", BCP 145, RFC 5405, DOI
 


Herbert, Yong, Zia        Expires March, 2019                  [Page 31]

Internet Draft         Generic UDP Encapsulation         August 31, 2018


              10.17487/RFC5405, November 2008, <http://www.rfc-
              editor.org/info/rfc5405>.

   [RFC6438]  Carpenter, B. and S. Amante, "Using the IPv6 Flow Label
              for Equal Cost Multipath Routing and Link Aggregation in
              Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011,
              <http://www.rfc-editor.org/info/rfc6438>.

   [RFC2003]  Perkins, C., "IP Encapsulation within IP", RFC 2003, DOI
              10.17487/RFC2003, October 1996, <http://www.rfc-
              editor.org/info/rfc2003>.

   [RFC3948]  Huttunen, A., Swander, B., Volpe, V., DiBurro, L., and M.
              Stenberg, "UDP Encapsulation of IPsec ESP Packets", RFC
              3948, DOI 10.17487/RFC3948, January 2005, <http://www.rfc-
              editor.org/info/rfc3948>.

   [RFC6830]  Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "The
              Locator/ID Separation Protocol (LISP)", RFC 6830, DOI
              10.17487/RFC6830, January 2013, <http://www.rfc-
              editor.org/info/rfc6830>.

   [RFC3378]  Housley, R. and S. Hollenbeck, "EtherIP: Tunneling
              Ethernet Frames in IP Datagrams", RFC 3378, DOI
              10.17487/RFC3378, September 2002, <http://www.rfc-
              editor.org/info/rfc3378>.

   [RFC2784]  Farinacci, D., Li, T., Hanks, S., Meyer, D., and P.
              Traina, "Generic Routing Encapsulation (GRE)", RFC 2784,
              DOI 10.17487/RFC2784, March 2000, <http://www.rfc-
              editor.org/info/rfc2784>.

   [RFC4023]  Worster, T., Rekhter, Y., and E. Rosen, Ed.,
              "Encapsulating MPLS in IP or Generic Routing Encapsulation
              (GRE)", RFC 4023, DOI 10.17487/RFC4023, March 2005,
              <http://www.rfc-editor.org/info/rfc4023>.

   [RFC2661]  Townsley, W., Valencia, A., Rubens, A., Pall, G., Zorn,
              G., and B. Palter, "Layer Two Tunneling Protocol "L2TP"",
              RFC 2661, DOI 10.17487/RFC2661, August 1999,
              <http://www.rfc-editor.org/info/rfc2661>.

   [RFC8084]  Fairhurst, G., "Network Transport Circuit Breakers", BCP
              208, RFC 8084, DOI 10.17487/RFC8084, March 2017,
              <https://www.rfc-editor.org/info/rfc8084>.

   [GUEEXTEN] Herbert, T., Yong, L., and Templin, F., "Extensions for
              Generic UDP Encapsulation" draft-herbert-gue-extensions-00
 


Herbert, Yong, Zia        Expires March, 2019                  [Page 32]

Internet Draft         Generic UDP Encapsulation         August 31, 2018


   [GUE4NVO3] Yong, L., Herbert, T., Zia, O., "Generic UDP Encapsulation
              (GUE) for Network Virtualization Overlay" draft-hy-nvo3-
              gue-4-nvo-03

   [GUESEC]   Yong, L., Herbert, T., "Generic UDP Encapsulation (GUE)
              for Secure Transport" draft-hy-gue-4-secure-transport-03

   [TCPUDP]   Chesire, S., Graessley, J., and McGuire, R.,
              "Encapsulation of TCP and other Transport Protocols over
              UDP" draft-cheshire-tcp-over-udp-00

   [TOU]      Herbert, T., "Transport layer protocols over UDP" draft-
              herbert-transports-over-udp-00

   [GENEVE]   Gross, J., Ed., Ganga, I. Ed., and Sridhar, T., "Geneve:
              Generic Network Virtualization Encapsulation", draft-ietf-
              nvo3-geneve-05

   [LCO]      Cree, E., https://www.kernel.org/doc/Documentation/
              networking/checksum-offloads.txt

Appendix A: NIC processing for GUE

   This appendix provides some guidelines for Network Interface Cards
   (NICs) to implement common offloads and accelerations to support GUE.
   Most of this discussion is generally applicable to other
   methods of UDP based encapsulation.
<!--  CEP: The last sentence means these discussions do not belong here.-->

A.1. Receive multi-queue

   Contemporary NICs support multiple receive descriptor queues (multi-
   queue). Multi-queue enables load balancing of network processing for
   a NIC across multiple CPUs. On packet reception, a NIC selects the
   appropriate queue for host processing. Receive Side Scaling is a
   common method which uses the flow hash for a packet to index an
   indirection table where each entry stores a queue number. Flow
   Director and Accelerated Receive Flow Steering (aRFS) allow a host to
   program the queue that is used for a given flow which is identified
   either by an explicit five-tuple or by the flow's hash.
<!--  CEP: citations needed for RSS, aRFS, etc.  -->

   GUE encapsulation is compatible with multi-queue NICs that support
   five-tuple hash calculation for UDP/IP packets as input to RSS. The
   flow entropy in the UDP source port ensures classification of the
   encapsulated flow even in the case that the outer source and
   destination addresses are the same for all flows (e.g. all flows are
   going over a single tunnel).

   By default, UDP RSS support is often disabled in NICs to avoid out-
 


Herbert, Yong, Zia        Expires March, 2019                  [Page 33]

Internet Draft         Generic UDP Encapsulation         August 31, 2018


   of-order reception that can occur when UDP packets are fragmented. As
<!--  CEP: citation needed for this claim.  -->
<!--  CEP: should explain why fragmented packets cause reordering. -->
   discussed above, fragmentation of GUE packets is mostly avoided by
   fragmenting packets before entering a tunnel, GUE fragmentation, path
<!--  CEP: This makes the case for specifying GUE fragmentation as part
           of this document.  -->
   MTU discovery in higher layer protocols, or operator adjusting MTUs.
   Other UDP traffic might not implement such procedures to avoid
   fragmentation, so enabling UDP RSS support in the NIC might be a
   considered tradeoff during configuration. 

A.2. Checksum offload

   Many NICs provide capabilities to calculate standard ones complement
   payload checksum for packets in transmit or receive. When using GUE
   encapsulation, there are at least two checksums that are of interest:
   the encapsulated packet's transport checksum, and the UDP checksum in
   the outer header.

A.2.1. Transmit checksum offload

   NICs can provide a protocol agnostic method to offload transmit
   checksum (NETIF_F_HW_CSUM in Linux parlance) that can be used with
   GUE. In this method, the host provides checksum related parameters in
   a transmit descriptor for a packet. These parameters include the
   starting offset of data to checksum, the length of data to checksum,
   and the offset in the packet where the computed checksum is to be
   written. The host initializes the checksum field to a pseudo header
   checksum.

   In the case of GUE, the checksum for an encapsulated transport layer
   packet, a TCP packet for instance, can be offloaded by setting the
   appropriate checksum parameters.

   NICs typically can offload only one transmit checksum per packet, so
   simultaneously offloading both an inner transport packet's checksum
   and the outer UDP checksum is likely not possible.

   If an encapsulator is co-resident with a host, then checksum offload
   may be performed using remote checksum offload (described in
   [GUEEXTEN]). Remote checksum offload relies on NIC offload of the
   simple UDP/IP checksum which is commonly supported even in legacy
   devices. In remote checksum offload, the outer UDP checksum is set
   and the GUE header includes an option indicating the start and offset
   of the inner "offloaded" checksum. The inner checksum is initialized
   to the pseudo header checksum. When a decapsulator receives a GUE
   packet with the remote checksum offload option, it completes the
   offload operation by determining the packet checksum from the
   indicated start point to the end of the packet, and then adds this
   into the checksum field at the offset given in the option. Computing
   the checksum from the start to end of packet is efficient if
 


Herbert, Yong, Zia        Expires March, 2019                  [Page 34]

Internet Draft         Generic UDP Encapsulation         August 31, 2018


   checksum-complete is provided on the receiver.

   Another alternative when an encapsulator is co-resident with a host
   is to perform Local Checksum Offload [LCO]. In this method, the inner
   transport layer checksum is offloaded and the outer UDP checksum can
   be deduced based on the fact that the portion of the packet covered
   by the inner transport checksum will sum to zero (or at least the bit
   wise "not" of the inner pseudo header).

A.2.2. Receive checksum offload

   GUE is compatible with NICs that perform a protocol agnostic receive
   checksum (CHECKSUM_COMPLETE in Linux parlance). In this technique, a
   NIC computes a ones complement checksum over all (or some predefined
   portion) of a packet. The computed value is provided to the host
   stack in the packet's receive descriptor. The host driver can use
   this checksum to "patch up" and validate any inner packet transport
   checksum, as well as the outer UDP checksum if it is non-zero.

   Many legacy NICs don't provide checksum-complete but instead provide
   an indication that a checksum has been verified (CHECKSUM_UNNECESSARY
   in Linux). Usually, such validation is only done for simple TCP/IP or
   UDP/IP packets. If a NIC indicates that a UDP checksum is valid, the
   checksum-complete value for the UDP packet is the "not" of the pseudo
   header checksum. In this way, checksum-unnecessary can be converted
   to checksum-complete. So, if the NIC provides checksum-unnecessary
   for the outer UDP header in an encapsulation, checksum conversion can
   be done so that the checksum-complete value is derived and can be
   used by the stack to validate checksums in the encapsulated packet.

A.3. Transmit Segmentation Offload

   Transmit Segmentation Offload (TSO) is a NIC feature where a host
   provides a large (>MTU size) TCP packet to the NIC, which in turn
   splits the packet into separate segments and transmits each one. This
   is useful to reduce CPU load on the host.
<!--  CEP: Citations needed!  -->

   The process of TSO can be generalized as:

      - Split the TCP payload into segments which allow packets with
        size less than or equal to MTU.

      - For each created segment:

        1. Replicate the TCP header and all preceding headers of the
           original packet.

        2. Set payload length fields in any headers to reflect the
 


Herbert, Yong, Zia        Expires March, 2019                  [Page 35]

Internet Draft         Generic UDP Encapsulation         August 31, 2018


           length of the segment.

        3. Set TCP sequence number to correctly reflect the offset of
           the TCP data in the stream.
<!--  CEP: This might conflict with the TCP sequence number chosen by
	   the TCP layer actually creating the segments.  -->

        4. Recompute and set any checksums that either cover the payload
           of the packet or cover header which was changed by setting a
           payload length.

   Following this general process, TSO can be extended to support TCP
   encapsulation in GUE.  For each segment the Ethernet, outer IP, UDP
   header, GUE header, inner IP header (if tunneling), and TCP headers
   are replicated. Any packet length header fields need to be set
   properly (including the length in the outer UDP header), and
   checksums need to be set correctly (including the outer UDP checksum
   if being used).

   To facilitate TSO with GUE, it is recommended that extension fields
   do not contain values that need to be updated on a per segment basis.
   For example, extension fields should not include checksums, lengths,
   or sequence numbers that refer to the payload. If the GUE header does
   not contain such fields then the TSO engine only needs to copy the
   bits in the GUE header when creating each segment and does not need
   to parse the GUE header. 
<!--  CEP: This makes appendix A.4 normative.  And if it's normative, it
	really needs to be in the main body of the text. -->

A.4. Large Receive Offload

   Large Receive Offload (LRO) is a NIC feature where packets of a TCP
   connection are reassembled, or coalesced, in the NIC and delivered to
   the host as one large packet. This feature can reduce CPU utilization
   in the host.
<!--  CEP: Citations needed!  -->

   LRO requires significant protocol awareness to be implemented
   correctly and is difficult to generalize. Packets in the same flow
   need to be unambiguously identified. In the presence of tunnels or
   network virtualization, this may require more than a five-tuple match
   (for instance packets for flows in two different virtual networks may
   have identical five-tuples). Additionally, a NIC needs to perform
   validation over packets that are being coalesced, and needs to
   fabricate a single meaningful header from all the coalesced packets.

   The conservative approach to supporting LRO for GUE would be to
   assign packets to the same flow only if they have identical five-
   tuple and were encapsulated the same way. That is the outer IP
   addresses, the outer UDP ports, GUE protocol, GUE flags and fields,
   and inner five tuple are all identical. 
<!--  CEP: sounds like this ought to be deleted.  -->

Appendix B: Implementation considerations
 


Herbert, Yong, Zia        Expires March, 2019                  [Page 36]

Internet Draft         Generic UDP Encapsulation         August 31, 2018


   This appendix is informational and does not constitute a normative
   part of this document.

B.1. Privileged ports

   Using the source port to contain a flow entropy value disallows the
   security method of a receiver enforcing that the source port be a
   privileged port. Privileged ports are defined by some operating
   systems to restrict source port binding. Unix, for instance,
   considered port number less than 1024 to be privileged.

   Enforcing that packets are sent from a privileged port is widely
   considered an inadequate security mechanism and has been mostly
   deprecated.
<!--  CEP: citation needed.  -->
               To approximate this behavior, an implementation could
   restrict a user from sending a packet destined to the GUE port
   without proper credentials.
<!--  CEP: this is not at all specific to GUE.  -->

B.2. Setting flow entropy as a route selector

   An encapsulator generating flow entropy in the outer UDP source port could
   modulate the value to perform a type of multipath source routing.
   Assuming that networking switches perform ECMP based on the flow
   hash, a sender can affect the path by altering the flow entropy.  For
   instance, a host can store a flow hash in its protocol control block
   (PCB) for an inner flow, and might alter the value upon detecting
   that packets are traversing a lossy path. Changing the flow entropy
   for a flow SHOULD be subject to hysteresis (at most once every thirty
   seconds) to limit the number of out of order packets.
<!--  CEP: If the appendix is not normative, it cannot place mandates.-->

B.3. Hardware protocol implementation considerations

   Low level data path protocols, such as GUE, are often supported in
   high speed network device hardware.  Variable length header (VLH)
   protocols like GUE are often considered difficult to efficiently
   implement in hardware. In order to retain the important
   characteristics of an extensible and robust protocol, hardware
   vendors may practice "constrained flexibility". In this model, only
   certain combinations or protocol header parameterizations are
   implemented in hardware fast path. Each such parameterization is
   fixed length so that the particular instance can be optimized as a
   fixed length protocol. In the case of GUE this constitutes specific
   combinations of GUE flags, fields, and next protocol. The selected
   combinations would naturally be the most common cases which form the
   "fast path", and other combinations are assumed to take the "slow
   path".

   In time, needs and requirements of the protocol may change which may
   manifest themselves as new parameterizations to be supported in the
 


Herbert, Yong, Zia        Expires March, 2019                  [Page 37]

Internet Draft         Generic UDP Encapsulation         August 31, 2018


   fast path. To allow this extensibility, a device practicing
   constrained flexibility should allow the fast path parameterizations
   to be programmable.
<!--  CEP: This appendix is very generic and could be deleted without
           harm.  -->

Authors' Addresses

   Tom Herbert
   Quantonium
   4701 Patrick Henry
   Santa Clara, CA 95054
   US

   Email: tom@xxxxxxxxxxxxxxx

   Lucy Yong
   Huawei USA
<!--  CEP: Lucy Yong is no longer a Huawei employee.  I suggest
	   moving her name to a Contributors section.  -->
   5340 Legacy Dr.
   Plano, TX 75024
   US

   Email: lucy.yong@xxxxxxxxxx

   Osama Zia
   Microsoft
   1 Microsoft Way
   Redmond, WA 98029
   US

   Email: osamaz@xxxxxxxxxxxxx






















Herbert, Yong, Zia        Expires March, 2019                  [Page 38]

<<< text/html; charset=UTF-8; name="Diff draft-ietf-intarea-gue-06.txt - draft-ietf-intarea-gue-06cepC.html": Unrecognized >>>

[Index of Archives]     [IETF Annoucements]     [IETF]     [IP Storage]     [Yosemite News]     [Linux SCTP]     [Linux Newbies]     [Mhonarc]     [Fedora Users]

  Powered by Linux