Reviewer: Carlos Bernardos
Review result: Ready with Nits
I think the document is well written and ready to move forward. I've
just inserted below (prepended with [CB]) some minor comments.
6man Z. Ali
Internet-Draft C. Filsfils
Intended status: Standards Track Cisco Systems
Expires: October 10, 2021 S. Matsushima
Softbank
D. Voyer
Bell Canada
M. Chen
Huawei
April 8, 2021
Operations, Administration, and Maintenance (OAM) in Segment Routing
Networks with IPv6 Data plane (SRv6)
draft-ietf-6man-spring-srv6-oam-10
Abstract
This document describes how the existing IPv6 mechanisms for ping and
traceroute can be used in an SRv6 network. The document also
specifies the OAM flag in the Segment Routing Header (SRH) for
performing controllable and predictable flow sampling from segment
endpoints. In addition, the document describes how a centralized
monitoring system performs a path continuity check between any nodes
within an SRv6 domain.
[CB] This is just a minor and personal comment (not intdir related): I'd
prefer starting with a more generic overall summary of what the
document does, and then the enumeration of the different parts. As
written now, it seems like a plain enumeration of things, which also
conveys the message of not being homogeneous.
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). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
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."
This Internet-Draft will expire on October 10, 2021.
Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://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.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
1.2. Abbreviations . . . . . . . . . . . . . . . . . . . . . . 3
1.3. Terminology and Reference Topology . . . . . . . . . . . 4
2. OAM Mechanisms . . . . . . . . . . . . . . . . . . . . . . . 5
2.1. O-flag in Segment Routing Header . . . . . . . . . . . . 5
2.1.1. O-flag Processing . . . . . . . . . . . . . . . . . . 6
2.2. OAM Operations . . . . . . . . . . . . . . . . . . . . . 7
3. Illustrations . . . . . . . . . . . . . . . . . . . . . . . . 8
3.1. Ping in SRv6 Networks . . . . . . . . . . . . . . . . . . 8
3.1.1. Classic Ping . . . . . . . . . . . . . . . . . . . . 8
3.1.2. Pinging a SID . . . . . . . . . . . . . . . . . . . . 10
3.2. Traceroute . . . . . . . . . . . . . . . . . . . . . . . 11
3.2.1. Classic Traceroute . . . . . . . . . . . . . . . . . 11
3.2.2. Traceroute to a SID . . . . . . . . . . . . . . . . . 13
3.3. A Hybrid OAM Using O-flag . . . . . . . . . . . . . . . . 15
3.4. Monitoring of SRv6 Paths . . . . . . . . . . . . . . . . 17
4. Implementation Status . . . . . . . . . . . . . . . . . . . . 18
5. Security Considerations . . . . . . . . . . . . . . . . . . . 18
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 19
8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 19
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 20
9.1. Normative References . . . . . . . . . . . . . . . . . . 21
9.2. Informative References . . . . . . . . . . . . . . . . . 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23
1. Introduction
As Segment Routing with IPv6 data plane (SRv6) [RFC8402] simply adds
a new type of Routing Extension Header, existing IPv6 OAM mechanisms
can be used in an SRv6 network. This document describes how the
existing IPv6 mechanisms for ping and traceroute can be used in an
SRv6 network. This includes illustrations of pinging an SRv6 SID to
verify that the SID is reachable and is locally programmed at the
target node. This also includes illustrations for tracerouting to an
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SRv6 SID for hop-by-hop fault localization as well as path tracing to
a SID.
The document also introduces enhancements for OAM mechanism for SRv6
networks for performing controllable and predictable flow sampling
from segment endpoints using, e.g., IP Flow Information Export
(IPFIX) protocol [RFC7011]. Specifically, the document specifies the
O-flag in SRH as a marking-bit in the user packets to trigger the
telemetry data collection and export at the segment endpoints.
The document also outlines how centralized OAM technique in [RFC8403]
[CB] Maybe "how the centralized OAM"?
can be extended for SRv6 to perform a path continuity check between
any nodes within an SRv6 domain. Specifically, the document
illustrates how a centralized monitoring system can monitor arbitrary
SRv6 paths by creating the loopback probes that originates and
terminates at the centralized monitoring system.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
1.2. Abbreviations
The following abbreviations are used in this document:
SID: Segment ID.
SL: Segments Left.
SR: Segment Routing.
SRH: Segment Routing Header [RFC8754].
SRv6: Segment Routing with IPv6 Data plane.
TC: Traffic Class.
ICMPv6: ICMPv6 Specification [RFC4443].
IS-IS: Intermediate System to Intermediate System
OSPF: Open Shortest Path First protocol [RFC2328]
IGP: Interior Gateway Protocols (e.g., OSPF, IS-IS).
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BGP-LS: Border Gateway Protocol - Link State Extensions [RFC8571]
[CB] I'd add the RFC where the SR-related terms/acronyms are originally
defined.
1.3. Terminology and Reference Topology
Throughout the document, the following terminology and simple
topology is used for illustration.
+--------------------------| N100 |---------------------------------+
| |
| ====== link1====== link3------ link5====== link9------ ====== |
||N1||------||N2||------| N3 |------||N4||------| N5 |---||N7||
|| ||------|| ||------| |------|| ||------| |---|| ||
====== link2====== link4------ link6======link10------ ======
| | | |
---+-- | ------ | --+---
|CE 1| +-------| N6 |---------+ |CE 2|
------ link7 | | link8 ------
------
Figure 1 Reference Topology
In the reference topology:
Node k has a IPv6 loopback address 2001:db8::A:k::/128.
Nodes N1, N2, N4 and N7 are SRv6-capable nodes.
Nodes N3, N5 and N6 are IPv6 nodes that are not SRv6-capable.
Such nodes are referred as classic IPv6 nodes.
CE1 and CE2 are Customer Edge devices of any data plane capability
(e.g., IPv4, IPv6, L2, etc.).
A SID at node k with locator block 2001:db8:B::/48 and function F
is represented by 2001:db8:B:k:F::.
Node N100 is a controller.
The IPv6 address of the nth Link between node i and j at the i
side is represented as 2001:db8:i:j:in::, e.g., the IPv6 address
of link6 (the 2nd link) between N3 and N4 at N3 in Figure 1 is
2001:db8:3:4:32::. Similarly, the IPv6 address of link5 (the 1st
link between N3 and N4) at node 3 is 2001:db8:3:4:31::.
2001:db8:B:k:Cij:: is explicitly allocated as the END.X SID at
node k towards neighbor node i via jth Link between node i and
node k. e.g., 2001:db8:B:2:C31:: represents END.X at N2 towards
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N3 via link3 (the 1st link between N2 and N3). Similarly,
2001:db8:B:4:C52:: represents the END.X at N4 towards N5 via
link10. Please refer to [RFC8986] for description of END.X SID.
A SID list is represented as <S1, S2, S3> where S1 is the first
SID to visit, S2 is the second SID to visit and S3 is the last SID
to visit along the SR path.
(SA,DA) (S3, S2, S1; SL)(payload) represents an IPv6 packet with:
* IPv6 header with source address SA, destination addresses DA
and SRH as next-header
* SRH with SID list <S1, S2, S3> with SegmentsLeft = SL
* Note the difference between the < > and () symbols: <S1, S2,
S3> represents a SID list where S1 is the first SID and S3 is
the last SID to traverse. (S3, S2, S1; SL) represents the same
SID list but encoded in the SRH format where the rightmost SID
in the SRH is the first SID and the leftmost SID in the SRH is
the last SID. When referring to an SR policy in a high-level
use-case, it is simpler to use the <S1, S2, S3> notation. When
referring to an illustration of the detailed packet behavior,
the (S3, S2, S1; SL) notation is more convenient.
* (payload) represents the the payload of the packet.
2. OAM Mechanisms
This section defines OAM enhancement for the SRv6 networks.
2.1. O-flag in Segment Routing Header
[RFC8754] describes the Segment Routing Header (SRH) and how SR
capable nodes use it. The SRH contains an 8-bit "Flags" field.
This document defines the following bit in the SRH Flags field to
carry the O-flag:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| |O| |
+-+-+-+-+-+-+-+-+
Where:
O-flag: OAM flag in the SRH Flags field defined in [RFC8754] .
[CB] Nit: \s\[RFC8754] .\[RFC8754].
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2.1.1. O-flag Processing
The O-flag in SRH is used as a marking-bit in the user packets to
trigger the telemetry data collection and export at the segment
endpoints.
[CB] Maybe this is obvious for someone expert in SRv6, but can only
telemetry data collection be done at segment endpoints?
This document does not specify the data elements that need to be
exported and the associated configurations. Similarly, this document
does not define any formats for exporting the data elements.
Nonetheless, without the loss of generality, this document assumes IP
Flow Information Export (IPFIX) protocol [RFC7011] is used for
exporting the traffic flow information from the network devices to a
controller for monitoring and analytics. Similarly, without the loss
of generality, this document assumes requested information elements
are configured by the management plane through data set templates
(e.g., as in IPFIX [RFC7012]).
Implementation of the O-flag is OPTIONAL. If a node does not support
the O-flag, then upon reception it simply ignores it. If a node
supports the O-flag, it can optionally advertise its potential via
control plane protocol(s).
When N receives a packet whose IPv6 DA is S and S is a local SID, the
line S01 of the pseudo-code associated with the SID S, as defined in
section 4.3.1.1 of [RFC8754], is appended as follows for the O-flag
processing.
S01.1. IF O-flag is set and local configuration permits
O-flag processing {
a. Make a copy of the packet.
b. Send the copied packet, along with a timestamp
to the OAM process for telemetry data collection
and export. ;; Ref1
}
Ref1: An implementation SHOULD copy and record the timestamp as
soon as possible during packet processing. Timestamp or any other
metadata is not
carried in the packet forwarded to the next hop.
[CB] Weird line jump above.
Please note that the O-flag processing happens before execution of
regular processing of the local SID S. Specifically, the line S01.1
of the pseudo-code specified in this document is inserted between
line S01 and S02 of the pseudo-code defined in section 4.3.1.1 of
[RFC8754].
Based on the requested information elements configured by the
management plane through data set templates [RFC7012], the OAM
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process exports the requested information elements. The information
elements include parts of the packet header and/or parts of the
packet payload for flow identification. The OAM process uses
information elements defined in IPFIX [RFC7011] and PSAMP [RFC5476]
for exporting the requested sections of the mirrored packets.
If the telemetry data from the ultimate segment in the segment-list
is required, a penultimate segment SHOULD NOT be a Penultimate
Segment Pop (PSP) SID. When the penultimate segment is a PSP SID,
the SRH will be removed and the O-flag will not be processed at the
ultimate segment.
The processing node SHOULD rate-limit the number of packets punted to
the OAM process to a configurable rate. This is to avoid hitting any
performance impact on the OAM and the telemetry collection processes.
Failure in implementing the rate limit can lead to a denial-of-
service attack, as detailed in Section 5.
The OAM process MUST NOT process the copy of the packet or respond to
any upper-layer header (like ICMP, UDP, etc.) payload to prevent
multiple evaluations of the datagram.
Specification of the OAM process or the external controller
operations are beyond the scope of this document. How to correlate
the data collected from different nodes at an external controller is
also outside the scope of the document. Section 3 illustrates use of
the O-flag for implementing a hybrid OAM mechanism, where the
"hybrid" classification is based on RFC7799 [RFC7799].
2.2. OAM Operations
IPv6 OAM operations can be performed for any SRv6 SID whose behavior
allows Upper Layer Header processing for an applicable OAM payload
(e.g., ICMP, UDP).
Ping to an SRv6 SID is used to verify that the SID is reachable and
is locally programmed at the target node. Traceroute to a SID is
used for hop-by-hop fault localization as well as path tracing to a
SID. Section 3 illustrates the ICMPv6 based ping and the UDP based
traceroute mechanisms for ping and traceroute to an SRv6 SID.
Although this document only illustrates ICMPv6 ping and UDP based
traceroute to an SRv6 SID, the procedures are equally applicable to
other IPv6 OAM probing to an SRv6 SID (e.g., Bidirectional Forwarding
Detection (BFD) [RFC5880], Seamless BFD (SBFD) [RFC7880], STAMP probe
message processing [I-D.gandhi-spring-stamp-srpm], etc.).
Specifically, as long as local configuration allows the Upper-layer
Header processing of the applicable OAM payload for SRv6 SIDs, the
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existing IPv6 OAM techniques can be used to target a probe to a
(remote) SID.
IPv6 OAM operations can be performed with the target SID in the IPv6
destination address without SRH or with SRH where the target SID is
the last segment. In general, OAM operations to a target SID may not
exercise all of its processing depending on its behavior definition.
For example, ping to an END.X SID [RFC8986] only validates the SID is
locally programmed at the target node and does not validate switching
to the correct outgoing interface. To exercise the behavior of a
target SID, the OAM operation SHOULD construct the probe in a manner
similar to a data packet that exercises the SID behavior, i.e. to
include that SID as a transit SID in either an SRH or IPv6 DA of an
outer IPv6 header or as appropriate based on the definition of the
SID behavior.
3. Illustrations
This section shows how some of the existing IPv6 OAM mechanisms can
be used in an SRv6 network. It also illustrates an OAM mechanism for
performing controllable and predictable flow sampling from segment
endpoints. How centralized OAM technique in [RFC8403] can be
extended for SRv6 is also described in this Section.
3.1. Ping in SRv6 Networks
The following subsections outline some use cases of the ICMPv6 ping
in the SRv6 networks.
3.1.1. Classic Ping
The existing mechanism to perform the reachability checks, along the
shortest path, continues to work without any modification. The
initiator may be an SRv6 node or a classic IPv6 node. Similarly, the
egress or transit may be an SRv6-capable node or a classic IPv6 node.
If an SRv6-capable ingress node wants to ping an IPv6 address via an
arbitrary segment list <S1, S2, S3>, it needs to initiate ICMPv6 ping
with an SR header containing the SID list <S1, S2, S3>. This is
illustrated using the topology in Figure 1. Assume all the links
have IGP metric 10 except both links between N2 and N3, which have
IGP metric set to 100. User issues a ping from node N1 to a loopback
of node 5, via segment list <2001:db8:B:2:C31::, 2001:db8:B:4:C52::>.
The SID behavior used in the example is End.X SID, as described in
[RFC8986], but the procedure is equally applicable to any other
(transit) SID type.
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Figure 2 contains sample output for a ping request initiated at node
N1 to the loopback address of node N5 via a segment list
<2001:db8:B:2:C31::, 2001:db8:B:4:C52::>.
> ping 2001:db8:A:5:: via segment-list 2001:db8:B:2:C31::,
2001:db8:B:4:C52::
Sending 5, 100-byte ICMPv6 Echos to B5::, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 0.625
/0.749/0.931 ms
Figure 2 A sample ping output at an SRv6-capable node
All transit nodes process the echo request message like any other
data packet carrying SR header and hence do not require any change.
Similarly, the egress node (IPv6 classic or SRv6-capable) does not
require any change to process the ICMPv6 echo request. For example,
in the ping example of Figure 2:
o Node N1 initiates an ICMPv6 ping packet with SRH as follows
(2001:db8:A:1::, 2001:db8:B:2:C31::) (2001:db8:A:5::,
2001:db8:B:4:C52::, 2001:db8:B:2:C31::, SL=2, NH = ICMPv6)(ICMPv6
Echo Request).
o Node N2, which is an SRv6-capable node, performs the standard SRH
processing. Specifically, it executes the END.X behavior
(2001:db8:B:2:C31::) and forwards the packet on link3 to N3.
o Node N3, which is a classic IPv6 node, performs the standard IPv6
processing. Specifically, it forwards the echo request based on
the DA 2001:db8:B:4:C52:: in the IPv6 header.
o Node N4, which is an SRv6-capable node, performs the standard SRH
processing. Specifically, it observes the END.X behavior
(2001:db8:B:4:C52::) and forwards the packet on link10 towards N5.
If 2001:db8:B:4:C52:: is a PSP SID, The penultimate node (Node N4)
does not, should not and cannot differentiate between the data
packets and OAM probes. Specifically, if 2001:db8:B:4:C52:: is a
PSP SID, node N4 executes the SID like any other data packet with
DA = 2001:db8:B:4:C52:: and removes the SRH.
o The echo request packet at N5 arrives as an IPv6 packet with or
without an SRH. If N5 receives the packet with SRH, it skips SRH
processing (SL=0). In either case, Node N5 performs the standard
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ICMPv6 processing on the echo request and responds with the echo
reply message to N1. The echo reply message is IP routed.
3.1.2. Pinging a SID
The classic ping described in the previous section applies equally to
perform SID reachability check and to validate the SID is locally
programmed at the target node. This is explained using an example in
the following. The example uses ping to an END SID, as described in
[RFC8986], but the procedure is equally applicable to ping any other
SID behaviors.
Consider the example where the user wants to ping a remote SID
2001:db8:B:4::, via 2001:db8:B:2:C31::, from node N1. The ICMPv6
echo request is processed at the individual nodes along the path as
follows:
o Node N1 initiates an ICMPv6 ping packet with SRH as follows
(2001:db8:A:1::, 2001:db8:B:2:C31::) (2001:db8:B:4::,
2001:db8:B:2:C31::; SL=1; NH=ICMPv6)(ICMPv6 Echo Request).
o Node N2, which is an SRv6-capable node, performs the standard SRH
processing. Specifically, it executes the END.X behavior
(2001:db8:B:2:C31::) on the echo request packet. If
2001:db8:B:2:C31:: is a PSP SID, node N4 executes the SID like any
other data packet with DA = 2001:db8:B:2:C31:: and removes the
SRH.
o Node N3, which is a classic IPv6 node, performs the standard IPv6
processing. Specifically, it forwards the echo request based on
DA = 2001:db8:B:4:: in the IPv6 header.
o When node N4 receives the packet, it processes the target SID
(2001:db8:B:4::).
o If the target SID (2001:db8:B:4::) is not locally instantiated,
the packet is discarded
o If the target SID (2001:db8:B:4::) is locally instantiated, the
node processes the upper layer header. As part of the upper layer
header processing node N4 respond to the ICMPv6 echo request
message and responds with the echo reply message. The echo reply
message is IP routed.
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3.2. Traceroute
There is no hardware or software change required for traceroute
operation at the classic IPv6 nodes in an SRv6 network. That
includes the classic IPv6 node with ingress, egress or transit roles.
Furthermore, no protocol changes are required to the standard
traceroute operations. In other words, existing traceroute
mechanisms work seamlessly in the SRv6 networks.
The following subsections outline some use cases of the traceroute in
the SRv6 networks.
3.2.1. Classic Traceroute
The existing mechanism to traceroute a remote IP address, along the
shortest path, continues to work without any modification. The
initiator may be an SRv6 node or a classic IPv6 node. Similarly, the
egress or transit may be an SRv6 node or a classic IPv6 node.
If an SRv6-capable ingress node wants to traceroute to IPv6 address
via an arbitrary segment list <S1, S2, S3>, it needs to initiate
traceroute probe with an SR header containing the SID list <S1, S2,
S3>. That is illustrated using the topology in Figure 1. Assume all
the links have IGP metric 10 except both links between N2 and N3,
which have IGP metric set to 100. User issues a traceroute from node
N1 to a loopback of node 5, via segment list <2001:db8:B:2:C31::,
2001:db8:B:4:C52::>. The SID behavior used in the example is End.X
SID, as described in [RFC8986], but the procedure is equally
applicable to any other (transit) SID type. Figure 3 contains sample
output for the traceroute request.
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> traceroute 2001:db8:A:5:: via segment-list 2001:db8:B:2:C31::,
2001:db8:B:4:C52::
Tracing the route to 2001:db8:A:5::
1 2001:db8:1:2:21:: 0.512 msec 0.425 msec 0.374 msec
DA: 2001:db8:B:2:C31::,
SRH:(2001:db8:A:5::, 2001:db8:B:4:C52::, 2001:db8:B:2:C31::, SL=2)
2 2001:db8:2:3:31:: 0.721 msec 0.810 msec 0.795 msec
DA: 2001:db8:B:4:C52::,
SRH:(2001:db8:A:5::, 2001:db8:B:4:C52::, 2001:db8:B:2:C31::, SL=1)
3 2001:db8:3:4::41:: 0.921 msec 0.816 msec 0.759 msec
DA: 2001:db8:B:4:C52::,
SRH:(2001:db8:A:5::, 2001:db8:B:4:C52::, 2001:db8:B:2:C31::, SL=1)
4 2001:db8:4:5::52:: 0.879 msec 0.916 msec 1.024 msec
DA: 2001:db8:A:5::
Figure 3 A sample traceroute output at an SRv6-capable node
In the sample traceroute output, the information displayed at each
hop is obtained using the contents of the "Time Exceeded" or
"Destination Unreachable" ICMPv6 responses. These ICMPv6 responses
are IP routed.
In the sample traceroute output, the information for link3 is
returned by N3, which is a classic IPv6 node. Nonetheless, the
ingress node is able to display SR header contents as the packet
travels through the IPv6 classic node. This is because the "Time
Exceeded Message" ICMPv6 message can contain as much of the invoking
packet as possible without the ICMPv6 packet exceeding the minimum
IPv6 MTU [RFC4443]. The SR header is also included in these ICMPv6
messages initiated by the classic IPv6 transit nodes that are not
running SRv6 software. Specifically, a node generating ICMPv6
message containing a copy of the invoking packet does not need to
understand the extension header(s) in the invoking packet.
The segment list information returned for the first hop is returned
by N2, which is an SRv6-capable node. Just like for the second hop,
the ingress node is able to display SR header contents for the first
hop.
There is no difference in processing of the traceroute probe at an
IPv6 classic node and an SRv6-capable node. Similarly, both IPv6
classic and SRv6-capable nodes may use the address of the interface
on which probe was received as the source address in the ICMPv6
response. ICMPv6 extensions defined in [RFC5837] can be used to also
display information about the IP interface through which the datagram
would have been forwarded had it been forwardable, and the IP next
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hop to which the datagram would have been forwarded, the IP interface
upon which a datagram arrived, the sub-IP component of an IP
interface upon which a datagram arrived.
The IP address of the interface on which the traceroute probe was
received is useful. This information can also be used to verify if
SIDs 2001:db8:B:2:C31:: and 2001:db8:B:4:C52:: are executed correctly
by N2 and N4, respectively. Specifically, the information displayed
for the second hop contains the incoming interface address
2001:db8:2:3:31:: at N3. This matches with the expected interface
bound to END.X behavior 2001:db8:B:2:C31:: (link3). Similarly, the
information displayed for hop5 contains the incoming interface
address 2001:db8:4:5::52:: at N5. This matches with the expected
interface bound to the END.X behavior 2001:db8:B:4:C52:: (link10).
3.2.2. Traceroute to a SID
The classic traceroute described in the previous section applies
equally to traceroute a remote SID behavior, as explained using an
example in the following. The example uses traceroute to an END SID,
as described in [RFC8986], but the procedure is equally applicable to
tracerouting any other SID behaviors.
Please note that traceroute to a SID is exemplified using UDP probes.
However, the procedure is equally applicable to other implementations
of traceroute mechanism. The UDP encoded message to traceroute a SID
uses the UDP ports assigned by IANA for "traceroute use".
Consider the example where the user wants to traceroute a remote SID
2001:db8:B:4::, via 2001:db8:B:2:C31::, from node N1. The traceroute
probe is processed at the individual nodes along the path as follows:
o Node N1 initiates a traceroute probe packet with a monotonically
increasing value of hop count and SRH as follows (2001:db8:A:1::,
2001:db8:B:2:C31::) (2001:db8:B:4::, 2001:db8:B:2:C31::; SL=1;
NH=UDP)(Traceroute probe).
o When node N2 receives the packet with hop-count = 1, it processes
the hop count expiry. Specifically, the node N2 responses with
the ICMPv6 message (Type: "Time Exceeded", Code: "Hop limit
exceeded in transit"). The ICMPv6 response is IP routed.
o When Node N2 receives the packet with hop-count > 1, it performs
the standard SRH processing. Specifically, it executes the END.X
behavior (2001:db8:B:2:C31::) on the traceroute probe. If
2001:db8:B:2:C31:: is a PSP SID, node N4 executes the SID like any
other data packet with DA = 2001:db8:B:2:C31:: and removes the
SRH.
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o When node N3, which is a classic IPv6 node, receives the packet
with hop-count = 1, it processes the hop count expiry.
Specifically, the node N3 responses with the ICMPv6 message (Type:
"Time Exceeded", Code: "Hop limit exceeded in Transit"). The
ICMPv6 response is IP routed.
o When node N3, which is a classic IPv6 node, receives the packet
with hop-count > 1, it performs the standard IPv6 processing.
Specifically, it forwards the traceroute probe based on DA
2001:db8:B:4:: in the IPv6 header.
o When node N4 receives the packet with DA set to the local SID
2001:db8:B:4::, it processes the END SID.
o If the target SID (2001:db8:B:4::) is not locally instantiated,
the packet is discarded.
o If the target SID (2001:db8:B:4::) is locally instantiated, the
node processes the upper layer header. As part of the upper layer
header processing node N4 responses with the ICMPv6 message (Type:
Destination unreachable, Code: Port Unreachable). The ICMPv6
response is IP routed.
Figure 4 displays a sample traceroute output for this example.
> traceroute 2001:db8:B:4:C52:: via segment-list 2001:db8:B:2:C31::
Tracing the route to SID 2001:db8:B:4:C52::
1 2001:db8:1:2:21:: 0.512 msec 0.425 msec 0.374 msec
DA: 2001:db8:B:2:C31::,
SRH:(2001:db8:B:4:C52::, 2001:db8:B:2:C31::; SL=1)
2 2001:db8:2:3:31:: 0.721 msec 0.810 msec 0.795 msec
DA: 2001:db8:B:4:C52::,
SRH:(2001:db8:B:4:C52::, 2001:db8:B:2:C31::; SL=0)
3 2001:db8:3:4:41:: 0.921 msec 0.816 msec 0.759 msec
DA: 2001:db8:B:4:C52::,
SRH:(2001:db8:B:4:C52::, 2001:db8:B:2:C31::; SL=0)
Figure 4 A sample output for hop-by-hop traceroute to a SID
[CB] Minor comment: since the sample outputs for both classic and traceroute to
a SID shows 3-values of the RTT, I'd probably mention somewhere that the
sample outputs assume sending 3x per hop-count, which is the typical
implementation approach (but I'm not sure this is recommended/mandated).
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3.3. A Hybrid OAM Using O-flag
This section illustrates a hybrid OAM mechanism using the the O-flag.
Without loss of the generality, the illustration assumes N100 is a
centralized controller.
The illustration is different than the In-situ OAM defined in [I.D-
draft-ietf-ippm-ioam-data]. This is because In-situ OAM records
operational and telemetry information in the packet as the packet
traverses a path between two points in the network [I.D-draft-ietf-
ippm-ioam-data]. The illustration in this subsection does not
require the recording of OAM data in the packet.
The illustration does not assume any formats for exporting the data
elements or the data elements that need to be exported.
Consider the example where the user wants to monitor sampled IPv4 VPN
999 traffic going from CE1 to CE2 via a low latency SR policy P
installed at Node N1. To exercise a low latency path, the SR Policy
P forces the packet via segments 2001:db8:B:2:C31:: and
2001:db8:B:4:C52::. The VPN SID at N7 associated with VPN 999 is
2001:db8:B:7:DT999::. 2001:db8:B:7:DT999:: is a USP SID. N1, N4,
and N7 are capable of processing O-flag but N2 is not capable of
processing O-flag. N100 is the centralized controller capable of
processing and correlating the copy of the packets sent from nodes
N1, N4, and N7. N100 is aware of O-flag processing capabilities.
Controller N100 with the help from nodes N1, N4, N7 and implements a
hybrid OAM mechanism using the O-flag as follows:
o A packet P1:(IPv4 header)(payload) is sent from CE1 to Node N1.
o Node N1 steers the packet P1 through the Policy P. Based on a
local configuration, Node N1 also implements logic to sample
traffic steered through policy P for hybrid OAM purposes.
Specification for the sampling logic is beyond the scope of this
document. Consider the case where packet P1 is classified as a
packet to be monitored via the hybrid OAM. Node N1 sets O-flag
during encapsulation required by policy P. As part of setting the
O-flag, node N1 also sends a timestamped copy of the packet P1:
(2001:db8:A:1::, 2001:db8:B:2:C31::) (2001:db8:B:7:DT999::,
2001:db8:B:4:C52::, 2001:db8:B:2:C31::; SL=2; O-flag=1;
NH=IPv4)(IPv4 header)(payload) to a local OAM process. The local
OAM process sends a full or partial copy of the packet P1 to the
controller N100. The OAM process includes the recorded timestamp,
additional OAM information like incoming and outgoing interface,
etc. along with any applicable metadata. Node N1 forwards the
original packet towards the next segment 2001:db8:B:2:C31::.
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o When node N2 receives the packet with O-flag set, it ignores the
O-flag. This is because node N2 is not capable of processing the
O-flag. Node N2 performs the standard SRv6 SID and SRH
processing. Specifically, it executes the END.X behavior
(2001:db8:B:2:C31::) as described in [RFC8986] and forwards the
packet P1 (2001:db8:A:1::, 2001:db8:B:4:C52::)
(2001:db8:B:7:DT999::, 2001:db8:B:4:C52::, 2001:db8:B:2:C31::;
SL=1; O-flag=1; NH=IPv4)(IPv4 header)(payload) over link 3 towards
Node N3.
o When node N3, which is a classic IPv6 node, receives the packet P1
, it performs the standard IPv6 processing. Specifically, it
forwards the packet P1 based on DA 2001:db8:B:4:C52:: in the IPv6
header.
[CB] Nit: \s\P1 ,\P1,
o When node N4 receives the packet P1 (2001:db8:A:1::,
2001:db8:B:4:C52::) (2001:db8:B:7:DT999::, 2001:db8:B:4:C52::,
2001:db8:B:2:C31::; SL=1; O-flag=1; NH=IPv4)(IPv4
header)(payload), it processes the O-flag. As part of processing
the O-flag, it sends a timestamped copy of the packet to a local
OAM process. The local OAM process sends a full or partial copy
of the packet P1 to the controller N100. The OAM process includes
the recorded timestamp, additional OAM information like incoming
and outgoing interface, etc. along with any applicable metadata.
Node N4 performs the standard SRv6 SID and SRH processing on the
original packet P1. Specifically, it executes the END.X behavior
(2001:db8:B:4:C52::) and forwards the packet P1 (2001:db8:A:1::,
2001:db8:B:7:DT999::) (2001:db8:B:7:DT999::, 2001:db8:B:4:C52::,
2001:db8:B:2:C31::; SL=0; O-flag=1; NH=IPv4)(IPv4 header)(payload)
over link 10 towards Node N5.
o When node N5, which is a classic IPv6 node, receives the packet
P1, it performs the standard IPv6 processing. Specifically, it
forwards the packet based on DA 2001:db8:B:7:DT999:: in the IPv6
header.
o When node N7 receives the packet P1 (2001:db8:A:1::,
2001:db8:B:7:DT999::) (2001:db8:B:7:DT999::, 2001:db8:B:4:C52::,
2001:db8:B:2:C31::; SL=0; O-flag=1; NH=IPv4)(IPv4
header)(payload), it processes the O-flag. As part of processing
the O-flag, it sends a timestamped copy of the packet to a local
OAM process. The local OAM process sends a full or partial copy
of the packet P1 to the controller N100. The OAM process includes
the recorded timestamp, additional OAM information like incoming
and outgoing interface, etc. along with any applicable metadata.
Node N4 performs the standard SRv6 SID and SRH processing on the
original packet P1. Specifically, it executes the VPN SID
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(2001:db8:B:7:DT999::) and based on lookup in table 100 forwards
the packet P1 (IPv4 header)(payload) towards CE 2.
o The controller N100 processes and correlates the copy of the
packets sent from nodes N1, N4 and N7 to find segment-by-segment
delays and provide other hybrid OAM information related to packet
P1.
o The process continues for any other sampled packets.
3.4. Monitoring of SRv6 Paths
In the recent past, network operators demonstrated interest in
performing network OAM functions in a centralized manner. [RFC8403]
describes such a centralized OAM mechanism. Specifically, the
document describes a procedure that can be used to perform path
continuity check between any nodes within an SR domain from a
centralized monitoring system. However, the document focuses on SR
networks with MPLS data plane. This document describes how the
concept can be used to perform path monitoring in an SRv6 network
from a centralized controller.
In the reference topology in Figure 1, N100 uses an IGP protocol like
OSPF or ISIS to get the topology view within the IGP domain. N100
can also use BGP-LS to get the complete view of an inter-domain
topology. The controller leverages the visibility of the topology to
monitor the paths between the various endpoints.
The controller N100 advertises an END SID [RFC8986]
2001:db8:B:100:1::. To monitor any arbitrary SRv6 paths, the
controller can create a loopback probe that originates and terminates
on Node N100. To distinguish between a failure in the monitored path
and loss of connectivity between the controller and the network, Node
N100 runs a suitable mechanism to monitor its connectivity to the
monitored network.
The loopback probes are exemplified using an example where controller
N100 needs to verify a segment list <2001:db8:B:2:C31::,
2001:db8:B:4:C52::>:
o N100 generates an OAM packet (2001:db8:A:100::,
2001:db8:B:2:C31::)(2001:db8:B:100:1::, 2001:db8:B:4:C52::,
2001:db8:B:2:C31::, SL=2)(OAM Payload). The controller routes the
probe packet towards the first segment, which is
2001:db8:B:2:C31::.
o Node N2 executes the END.X behavior (2001:db8:B:2:C31::) and
forwards the packet (2001:db8:A:100::,
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2001:db8:B:4:C52::)(2001:db8:B:100:1::, 2001:db8:B:4:C52::,
2001:db8:B:2:C31::, SL=1)(OAM Payload) on link3 to N3.
o Node N3, which is a classic IPv6 node, performs the standard IPv6
processing. Specifically, it forwards the packet based on the DA
2001:db8:B:4:C52:: in the IPv6 header.
o Node N4 executes the END.X behavior (2001:db8:B:4:C52::) and
forwards the packet (2001:db8:A:100::,
2001:db8:B:100:1::)(2001:db8:B:100:1::, 2001:db8:B:4:C52::,
2001:db8:B:2:C31::, SL=0)(OAM Payload) on link10 to N5.
o Node N5, which is a classic IPv6 node, performs the standard IPv6
processing. Specifically, it forwards the packet based on the DA
2001:db8:B:100:1:: in the IPv6 header.
o Node N100 executes the standard SRv6 END behavior. It
decapsulates the header and consume the probe for OAM processing.
The information in the OAM payload is used to detect any missing
probes, round trip delay, etc.
The OAM payload type or the information carried in the OAM probe is a
local implementation decision at the controller and is outside the
scope of this document.
4. Implementation Status
This section is to be removed prior to publishing as an RFC.
See [I-D.matsushima-spring-srv6-deployment-status] for updated
deployment and interoperability reports.
5. Security Considerations
This document does not define any new protocol extensions and relies
on existing procedures defined for ICMPv6.
[RFC8754] defines the notion of an SR domain and use of SRH within
the SR domain. The use of OAM procedures described in this document
is restricted to an SR domain. For example, similar to the SID
manipulation, O-flag manipulation is not considered as a threat
within the SR domain. Procedures for securing an SR domain are
defined the section 5.1 and section 7 of [RFC8754].
As noted in section 7.1 of [RFC8754], compromised nodes within the SR
domain may mount attacks. The O-flag may be set by an attacking node
attempting a denial-of-service attack on the OAM process at the
segment endpoint node. An implementation correctly implementing the
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rate limiting in section 2.1.1 is not susceptible to that denial-of-
service attack. Additionally, SRH Flags are protected by the HMAC
TLV, as described in Section 2.1.2.1 of [RFC8754].
This document does not impose any additional security challenges to
be considered beyond security threats described in [RFC4884],
[RFC4443], [RFC0792], and [RFC8754].
6. IANA Considerations
This document requests that IANA allocate the following registrations
in the "Segment Routing Header Flags" sub-registry for the "Internet
Protocol Version 6 (IPv6) Parameters" registry maintained by IANA:
+-------+------------------------------+---------------+
| Bit | Description | Reference |
+=======+==============================+===============+
| 2 | O-flag | This document |
+-------+------------------------------+---------------+
7. Acknowledgements
The authors would like to thank Joel M. Halpern, Greg Mirsky, Bob
Hinden, Loa Andersson, Gaurav Naik, Ketan Talaulikar and Haoyu Song
for their review comments.
8. Contributors
The following people have contributed to this document:
Robert Raszuk
Bloomberg LP
Email: robert@xxxxxxxxxx
John Leddy
Individual
Email: john@xxxxxxxxx
Gaurav Dawra
LinkedIn
Email: gdawra.ietf@xxxxxxxxx
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Bart Peirens
Proximus
Email: bart.peirens@xxxxxxxxxxxx
Nagendra Kumar
Cisco Systems, Inc.
Email: naikumar@xxxxxxxxx
Carlos Pignataro
Cisco Systems, Inc.
Email: cpignata@xxxxxxxxx
Rakesh Gandhi
Cisco Systems, Inc.
Canada
Email: rgandhi@xxxxxxxxx
Frank Brockners
Cisco Systems, Inc.
Germany
Email: fbrockne@xxxxxxxxx
Darren Dukes
Cisco Systems, Inc.
Email: ddukes@xxxxxxxxx
Cheng Li
Huawei
Email: chengli13@xxxxxxxxxx
Faisal Iqbal
Individual
Email: faisal.ietf@xxxxxxxxx
9. References
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9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
(SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
<https://www.rfc-editor.org/info/rfc8754>.
9.2. Informative References
[I-D.gandhi-spring-stamp-srpm]
Gandhi, R., Filsfils, C., Voyer, D., Chen, M., and B.
Janssens, "Performance Measurement Using Simple TWAMP
(STAMP) for Segment Routing Networks", draft-gandhi-
spring-stamp-srpm-04 (work in progress), January 2021.
[I-D.ietf-ippm-ioam-data]
Brockners, F., Bhandari, S., and T. Mizrahi, "Data Fields
for In-situ OAM", draft-ietf-ippm-ioam-data-11 (work in
progress), November 2020.
[I-D.matsushima-spring-srv6-deployment-status]
Matsushima, S., Filsfils, C., Ali, Z., Li, Z., and K.
Rajaraman, "SRv6 Implementation and Deployment Status",
draft-matsushima-spring-srv6-deployment-status-10 (work in
progress), December 2020.
[RFC0792] Postel, J., "Internet Control Message Protocol", STD 5,
RFC 792, DOI 10.17487/RFC0792, September 1981,
<https://www.rfc-editor.org/info/rfc792>.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328,
DOI 10.17487/RFC2328, April 1998,
<https://www.rfc-editor.org/info/rfc2328>.
[RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet
Control Message Protocol (ICMPv6) for the Internet
Protocol Version 6 (IPv6) Specification", STD 89,
RFC 4443, DOI 10.17487/RFC4443, March 2006,
<https://www.rfc-editor.org/info/rfc4443>.
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[RFC4884] Bonica, R., Gan, D., Tappan, D., and C. Pignataro,
"Extended ICMP to Support Multi-Part Messages", RFC 4884,
DOI 10.17487/RFC4884, April 2007,
<https://www.rfc-editor.org/info/rfc4884>.
[RFC5476] Claise, B., Ed., Johnson, A., and J. Quittek, "Packet
Sampling (PSAMP) Protocol Specifications", RFC 5476,
DOI 10.17487/RFC5476, March 2009,
<https://www.rfc-editor.org/info/rfc5476>.
[RFC5837] Atlas, A., Ed., Bonica, R., Ed., Pignataro, C., Ed., Shen,
N., and JR. Rivers, "Extending ICMP for Interface and
Next-Hop Identification", RFC 5837, DOI 10.17487/RFC5837,
April 2010, <https://www.rfc-editor.org/info/rfc5837>.
[RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,
<https://www.rfc-editor.org/info/rfc5880>.
[RFC7011] Claise, B., Ed., Trammell, B., Ed., and P. Aitken,
"Specification of the IP Flow Information Export (IPFIX)
Protocol for the Exchange of Flow Information", STD 77,
RFC 7011, DOI 10.17487/RFC7011, September 2013,
<https://www.rfc-editor.org/info/rfc7011>.
[RFC7012] Claise, B., Ed. and B. Trammell, Ed., "Information Model
for IP Flow Information Export (IPFIX)", RFC 7012,
DOI 10.17487/RFC7012, September 2013,
<https://www.rfc-editor.org/info/rfc7012>.
[RFC7799] Morton, A., "Active and Passive Metrics and Methods (with
Hybrid Types In-Between)", RFC 7799, DOI 10.17487/RFC7799,
May 2016, <https://www.rfc-editor.org/info/rfc7799>.
[RFC7880] Pignataro, C., Ward, D., Akiya, N., Bhatia, M., and S.
Pallagatti, "Seamless Bidirectional Forwarding Detection
(S-BFD)", RFC 7880, DOI 10.17487/RFC7880, July 2016,
<https://www.rfc-editor.org/info/rfc7880>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/info/rfc8402>.
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[RFC8403] Geib, R., Ed., Filsfils, C., Pignataro, C., Ed., and N.
Kumar, "A Scalable and Topology-Aware MPLS Data-Plane
Monitoring System", RFC 8403, DOI 10.17487/RFC8403, July
2018, <https://www.rfc-editor.org/info/rfc8403>.
[RFC8571] Ginsberg, L., Ed., Previdi, S., Wu, Q., Tantsura, J., and
C. Filsfils, "BGP - Link State (BGP-LS) Advertisement of
IGP Traffic Engineering Performance Metric Extensions",
RFC 8571, DOI 10.17487/RFC8571, March 2019,
<https://www.rfc-editor.org/info/rfc8571>.
[RFC8986] Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer,
D., Matsushima, S., and Z. Li, "Segment Routing over IPv6
(SRv6) Network Programming", RFC 8986,
DOI 10.17487/RFC8986, February 2021,
<https://www.rfc-editor.org/info/rfc8986>.
Authors' Addresses
Zafar Ali
Cisco Systems
Email: zali@xxxxxxxxx
Clarence Filsfils
Cisco Systems
Email: cfilsfil@xxxxxxxxx
Satoru Matsushima
Softbank
Email: satoru.matsushima@xxxxxxxxxxxxxxxx
Daniel Voyer
Bell Canada
Email: daniel.voyer@xxxxxxx
Mach Chen
Huawei
Email: mach.chen@xxxxxxxxxx
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