Hi Daniel,
thank you for your kind consideration of my notes. I've top-copied what appeared to me as the remaining open issues. I hope I've not missed any of your questions. Please find my notes in-line below tagged GIM>>. Attached are the updated working version and the new diff.
Regards,
Greg
<mglt>
sure. If you know the network is down, then fast fail-over is definitively a plus. What I think could be useful is to evaluate the cost associated to a fast-fail-over without any network failure. This would be useful for an operator to evaluate whether it should spend more time in diagnosing a network failure versus performing a fast-fail-over.
Typically, if a fast failover comes a no cost at all, one operator would maybe use one exchange to test the liveness of a node rather than 3.
At that point, it seems to me that additional text coudl be added to characterize the impact. These could be high level and indicative, but it seems to me that knowing these impacts presents some value to the operators.
</mglt>
sure. If you know the network is down, then fast fail-over is definitively a plus. What I think could be useful is to evaluate the cost associated to a fast-fail-over without any network failure. This would be useful for an operator to evaluate whether it should spend more time in diagnosing a network failure versus performing a fast-fail-over.
Typically, if a fast failover comes a no cost at all, one operator would maybe use one exchange to test the liveness of a node rather than 3.
At that point, it seems to me that additional text coudl be added to characterize the impact. These could be high level and indicative, but it seems to me that knowing these impacts presents some value to the operators.
</mglt>
GIM>> I would like to add a new paragraph in Section 3.1:
NEW TEXT:
All methods described in this section may produce false-negative
state changes that can be the trigger for an unnecessary failover
negatively impacting the multicast service provided by the VPN. An
operator expected to consider the network environment and use
available controls of the mechanism used to determine the status of a
P-tunnel.
state changes that can be the trigger for an unnecessary failover
negatively impacting the multicast service provided by the VPN. An
operator expected to consider the network environment and use
available controls of the mechanism used to determine the status of a
P-tunnel.
Would the new text be helpful?
<mglt>
Thanks for the feed back, It seems to me important to mention it is not recommended these two mechanism co-exist.
How to avoid false negative transition might be out of scope of the draft I agree, but it seems to me worth being mentioned especially in relation to the impacts associated to a fail-over. In case the fast-failover comes with no impact this becomes less of a problem for operator deploying it.
</mglt>
Thanks for the feed back, It seems to me important to mention it is not recommended these two mechanism co-exist.
How to avoid false negative transition might be out of scope of the draft I agree, but it seems to me worth being mentioned especially in relation to the impacts associated to a fail-over. In case the fast-failover comes with no impact this becomes less of a problem for operator deploying it.
</mglt>
GIM>> I hope that the new text presented above addresses this concern.
<mglt>
I understand the document is addressing a 1:N scenario. That said, if M:N scenario leverage from 1:N protection it seems to me worth raising the issue.
</mglt>
I understand the document is addressing a 1:N scenario. That said, if M:N scenario leverage from 1:N protection it seems to me worth raising the issue.
</mglt>
GIM>> I propose adding the clarification of the use of the Sandby PE in Section 4:
OLD TEXT:
The procedures described below are limited to the case where the site
that contains C-S is connected to two or more PEs, though, to
simplify the description, the case of dual-homing is described.
that contains C-S is connected to two or more PEs, though, to
simplify the description, the case of dual-homing is described.
NEW TEXT:
The procedures described below are limited to the case where the site
that contains C-S is connected to two or more PEs, though, to
simplify the description, the case of dual-homing is described. Such
a redundancy protection scheme, referred to as 1:N protection, is the
special case of M:N protection, where M working instances are sharing
protection of the N standby instances. In addition to a network
failure detection mechanism, the latter scheme requires using a
mechanism to coordinate the failover among working instances. For
that reason, M:N protection is outside the scope of this
specification.
that contains C-S is connected to two or more PEs, though, to
simplify the description, the case of dual-homing is described. Such
a redundancy protection scheme, referred to as 1:N protection, is the
special case of M:N protection, where M working instances are sharing
protection of the N standby instances. In addition to a network
failure detection mechanism, the latter scheme requires using a
mechanism to coordinate the failover among working instances. For
that reason, M:N protection is outside the scope of this
specification.
On Wed, Nov 11, 2020 at 8:48 AM Daniel Migault <daniel.migault@xxxxxxxxxxxx> wrote:
Hi Greg,
Thanks for the response and clarifications. Most of my comments have been addressed/answered. However, it seems to me that some additional text might be added to the security consideration section document the impact on the network of a fast-failover operation. The knowledge of these impact might be useful for an operator to determine when the trigger can be done.
Please see more comments inline.
Yours,
Daniel
From: Greg Mirsky <gregimirsky@xxxxxxxxx>
Sent: Tuesday, November 10, 2020 9:13 PM
To: Daniel Migault <daniel.migault@xxxxxxxxxxxx>
Cc: secdir@xxxxxxxx <secdir@xxxxxxxx>; BESS <bess@xxxxxxxx>; last-call@xxxxxxxx <last-call@xxxxxxxx>; draft-ietf-bess-mvpn-fast-failover.all@xxxxxxxx <draft-ietf-bess-mvpn-fast-failover.all@xxxxxxxx>
Subject: Re: Secdir last call review of draft-ietf-bess-mvpn-fast-failover-11Hi Daniel,many thanks for the review, thoughtful comments, and questions, all are much appreciated. Also, my apologies for the long delay to respond to your comments. Please find my answers and notes in-line below tagged by GIM>>. Attached are the new working version and the diff to -12.
Regards,Greg
On Fri, Oct 23, 2020 at 5:36 AM Daniel Migault via Datatracker <noreply@xxxxxxxx> wrote:
Reviewer: Daniel Migault
Review result: Has Nits
Hi,
I reviewed this document as part of the Security Directorate's ongoing effort to
review all IETF documents being processed by the IESG. These comments were
written primarily for the benefit of the Security Area Directors. Document
authors, document editors, and WG chairs should treat these comments just like
any other IETF Last Call comments. Please note also that my expertise in BGP is
limited, so feel free to take these comments with a pitch of salt.
Review Results: Has Nits
Please find my comments below.
Yours,
Daniel
Multicast VPN Fast Upstream Failover
draft-ietf-bess-mvpn-fast-failover-11
Abstract
This document defines multicast VPN extensions and procedures that
allow fast failover for upstream failures, by allowing downstream PEs
to take into account the status of Provider-Tunnels (P-tunnels) when
selecting the Upstream PE for a VPN multicast flow, and extending BGP
MVPN routing so that a C-multicast route can be advertised toward a
Standby Upstream PE.
<mglt>
Though it might be just a nit, if MVPN
designates multicast VPN, it might be
clarifying to specify the acronym in the
first sentence. This would later make
the correlation with BGP MVPN clearer.
</mglt>
GIM>> I've updated s/BGP MVPN/BGP multicast VPN/. Also, s/mVPN/MVPN/ throughout the document.
1. Introduction
In the context of multicast in BGP/MPLS VPNs, it is desirable to
provide mechanisms allowing fast recovery of connectivity on
different types of failures. This document addresses failures of
elements in the provider network that are upstream of PEs connected
to VPN sites with receivers.
<mglt>
Well I am not familiar with neither BGP
nor MPLS. It seems that BGP/MLPS IP VPNS
and MPLS/BGP IP VPNs are both used. I am
wondering if there is a distinction
between the two and a preferred way to
designate these VPNs. My understanding
is that the VPN-IPv4 characterizes the
VPN while MPLS is used by the backbone
for the transport. Since the PE are
connected to the backbone the VPN-IPv4
needs to be labeled.
</mglt>
GIM>> I understand that this document often sends the reader to check RFC 6513 and/or RFC 6514. BGP/MPLS MVPN identifies the case of providing a multicast service over an IP VPN that is overlayed on the MPLS data plane using the BGP control plane.
Section 3 describes local procedures allowing an egress PE (a PE
connected to a receiver site) to take into account the status of
P-tunnels to determine the Upstream Multicast Hop (UMH) for a given
(C-S, C-G). This method does not provide a "fast failover" solution
<mglt>
I understand the limitation is due to
BGP convergence.
</mglt>
GIM>> Yes, a dynamic routing protocol, BGP in this case, provides the service restoration functionality but the restoration time is significant and affects the experience of a client.
when used alone, but can be used together with the mechanism
described in Section 4 for a "fast failover" solution.
Section 4 describes protocol extensions that can speed up failover by
not requiring any multicast VPN routing message exchange at recovery
time.
Moreover, section 5 describes a "hot leaf standby" mechanism, that
uses a combination of these two mechanisms. This approach has
similarities with the solution described in [RFC7431] to improve
failover times when PIM routing is used in a network given some
topology and metric constraints.
[...]
3.1.1. mVPN Tunnel Root Tracking
A condition to consider that the status of a P-tunnel is up is that
the root of the tunnel, as determined in the x-PMSI Tunnel attribute,
is reachable through unicast routing tables. In this case, the
downstream PE can immediately update its UMH when the reachability
condition changes.
That is similar to BGP next-hop tracking for VPN routes, except that
the address considered is not the BGP next-hop address, but the root
address in the x-PMSI Tunnel attribute.
If BGP next-hop tracking is done for VPN routes and the root address
of a given tunnel happens to be the same as the next-hop address in
the BGP A-D Route advertising the tunnel, then checking, in unicast
routing tables, whether the tunnel root is reachable, will be
unnecessary duplication and thus will not bring any specific benefit.
<mglt>
It seems to me that x-PMSI address
designates a different interface than
the one used by the Tunnel itself. If
that is correct, such mechanisms seems
to assume that one equipment up on one
interface will be up on the other
interfaces. I have the impression that a
configuration change in a PE may end up
in the P-tunnel being down, while the PE
still being reachable though the x-PMSI
Tunnel attribute. If that is a possible
scenario, the current mechanisms may not
provide more efficient mechanism than
then those of the standard BGP.
GIM>> That is a very interesting angle, thank you. Yes, in OAM, and in the Fault Management (FM) OAM in particular, we have to make some assumptions about the state of the remote system based on a single event or change of state. Usually, AFAIK, operators use not a physical interface but a loopback to associate with a tunnel. With a fast IGP convergence, a loopback interface is reachable as long as there's a path through the network between two nodes.<mglt>Thanks for the clarification</mglt>
Similarly, it is assumed the tunnel is
either up or down and the determination
of not being up if being down. I am not
convinced that the two only states.
Typically services under DDoS may be
down for a small amount of time. While
this affects the network, there is not
always a clear cut between the PE being
up or down.
</mglt>
GIM>> In defect detection a system often has some hysteresis, i.e., time that the system has to wait to change its state. For example, BFD changes state from Up to Down after the system does not receive N consecutive packets (usually 3). As a result, in some cases, the system can be tuned to detect relatively short outages while in others be slower and miss short-lived outages.
[...]
3.1.6. BFD Discriminator Attribute
P-tunnel status may be derived from the status of a multipoint BFD
session [RFC8562] whose discriminator is advertised along with an
x-PMSI A-D Route.
This document defines the format and ways of using a new BGP
attribute called the "BFD Discriminator". It is an optional
transitive BGP attribute. In Section 7.2, IANA is requested to
allocate the codepoint value (TBA2). The format of this attribute is
shown in Figure 1.
<mglt>
I feel that the sentence "In Section ...
TBA2)." should be removed.
</mglt>
GIM>> We use this to mark where to note the allocated value. Usually, this text is replaced by the RFC Editor to readIn Section 7.2 IANA allocated codepoint XXX.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BFD Mode | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BFD Discriminator |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Optional TLVs ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Format of the BFD Discriminator Attribute
Where:
BFD Mode field is the one octet long. This specification defines
the P2MP BFD Session as value 1 Section 7.2.
Reserved field is three octets long, and the value MUST be zeroed
on transmission and ignored on receipt.
BFD Discriminator field is four octets long.
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Optional TLVs is the optional variable-length field that MAY be
used in the BFD Discriminator attribute for future extensions.
TLVs MAY be included in a sequential or nested manner. To allow
for TLV nesting, it is advised to define a new TLV as a variable-
length object. Figure 2 presents the Optional TLV format TLV that
consists of:
* one octet-long field of TLV 's Type value (Section 7.3)
* one octet-long field of the length of the Value field in octets
* variable length Value field.
The length of a TLV MUST be multiple of four octets.
<mglt>
I am wondering why the constraint on the
length is not mentioned in the paragraph
associated to the field - as opposed to
a separate paragraph.
</mglt>
GIM>> There might be a slight confusion due to the use of Length and length. Capitalized - the name of the field which value is the length of the Value field. The last sentence refers to the overall length of a TLV, including lengths of Type, Length and Value fields.
<mglt>you are correct that might have confused me.</mglt>
[..]
8. Security Considerations
This document describes procedures based on [RFC6513] and [RFC6514]
and hence shares the security considerations respectively represented
in these specifications.
This document uses p2mp BFD, as defined in [RFC8562], which, in turn,
is based on [RFC5880]. Security considerations relevant to each
protocol are discussed in the respective protocol specifications. An
implementation that supports this specification MUST use a mechanism
to control the maximum number of p2mp BFD sessions that can be active
at the same time.
<mglt>
At a high level view - or at least my
interpretation of it - the document
proposes a mechanism based on BFD to
detect fault in the path. Upon a fault
detection a fail-over operation is
instructed using BGP. This rocedure is
expected to perform a faster fail-over
than traditional BGP convergence on
maintaining routing tables. Once the
fail over has been performed, BFD is
confirms the new path is "legitimate"
and works.
It seems correct to me that the current
protocol relies on BGP / BFD security.
That said, having BFD authentication
based on MD5 or SHA1 may suggest that
stronger primitives be recommended.
While this does not concerns the current
document, it seems to me that the
information might be relayed to routing
ADs.
What remains unclear to me - and I
assume this might be due to my lake or
expertise in routing area - is the impact
associated to performing a fail-over
both on 1) the data plane and 2) the
standard BGP way to establish routing
tables.
Regarding the data plane, I am wondering
if fail-over results in a lost of
packets for example - I suppose for
example that at least the packets in the
process of being forwarded might be
lost. I believe that providing details
on this may be good.
GIM>> You bring up a very topic for the discussion, thank you. With network failure detection in place, the fail-over can be viewed as the reaction to a network failure. If that is the case, then packet loss experienced by service due to the fail-over is the result of the network failure. Would you agree with that view? A shorter failure detection interval and faster fail-over should minimize the packet loss and, as a result, the negative impact on the service itself.
<mglt>sure. If you know the network is down, then fast fail-over is definitively a plus. What I think could be useful is to evaluate the cost associated to a fast-fail-over without any network failure. This would be useful for an operator to evaluate whether it should spend more time in diagnosing a network failure versus performing a fast-fail-over.Typically, if a fast failover comes a no cost at all, one operator would maybe use one exchange to test the liveness of a node rather than 3.
At that point, it seems to me that additional text coudl be added to characterize the impact. These could be high level and indicative, but it seems to me that knowing these impacts presents some value to the operators.</mglt>
If there are any impacts I would like to
understand also in which cases the
decision to perform a failover operation
may result in more harm than the event
that has been over-interpreted. An
hypothetical scenario could be that the
non reception of a BFD packet is
interpreted as a PE being down while it
may not be correct and the PE might have
been simply under stress. A "too fast" fail-over
may over interpreted it and perform a
fail-over. If such things could happen,
an attacker could leverage a micro event
to perform network operation that are
not negligible. Another way to see that
is that an attacker might not have
direct access to the control plan, but
could use the data plan to generate a
stress and sort of control the fail
over. It seems to me that some text
might be welcome to prevent such cases
to happen. This could be guidance for
declaring a tunnel down for example.
GIM>> I agree with your scenario. Over-short detection interval may produce a false-negative transition to the Down state in BFD and thus triggering the fail-over. I think that that is more an operational issue, something that an operator will consider when deploying the mechanism specified in this draft. Resulting from addressing RtgDir review the draft was updated to provide more guidance:In many cases, it is not practical to use both protection
methods at the same time because uncorrelated timers might cause
unnecessary switchovers and destabilize the network.
<mglt>Thanks for the feed back, It seems to me important to mention it is not recommended these two mechanism co-exist.How to avoid false negative transition might be out of scope of the draft I agree, but it seems to me worth being mentioned especially in relation to the impacts associated to a fail-over. In case the fast-failover comes with no impact this becomes less of a problem for operator deploying it.</mglt>Though the text above might not be general, I think that it also applies to the scenario you've presented.
Similarly, it would be good to add some
text regarding the interferences with
the non-fast forwarding fail over when
performed by the standard BGP.
Typically, my impression is that the
fast fail-over mechanism is a local
decision versus the BGP convergence that
is more global. As a result, even with
more time this two mechanisms may come
with different outcomes. One such
example to illustrate my purpose could
be the following. Note that this is only
illustrative of my purpose, and I let
you find and pick on ethat is more
appropriated. I am thinking of a case
where a standby PE is be shared among
multiple PEs - supposing this situation
could occur. Typically, if PE_1, PE_2
are shared by PE_a, ..., PE_z. In case
PE_a and PE_b are down, we expect PE_a
to switch to PE_1 and PE_b to switch to
PE_2. It seems to me that BGP would end
up in such situation while a local
decision may end up in PE_a and PE_a to
switch to PE_1.
</mglt>
GIM>> Thank you for the scenario that is very common in deploying protection based on the shared redundant resources. Such schemes, referred to as M:N protection, in addition to using mechanism detecting a network failure, e.g., BFD, require a protocol to coordinate the switchover. This specification applies to a more special deployment scenario where one working PE is protected by one or more standby PEs, i.e., 1:N protection.
<mglt>I understand the document is addressing a 1:N scenario. That said, if M:N scenario leverage from 1:N protection it seems to me worth raising the issue.</mglt>
Network Working Group T. Morin, Ed.
Internet-Draft Orange
Intended status: Standards Track R. Kebler, Ed.
Expires: May 16, 2021 Juniper Networks
G. Mirsky, Ed.
ZTE Corp.
November 12, 2020
Multicast VPN Fast Upstream Failover
draft-ietf-bess-mvpn-fast-failover-13
Abstract
This document defines multicast VPN extensions and procedures that
allow fast failover for upstream failures by allowing downstream PEs
to consider the status of Provider-Tunnels (P-tunnels) when selecting
the upstream PE for a VPN multicast flow. The fast failover is
enabled by using RFC 8562 BFD for Multipoint Networks and the new BGP
Attribute - BFD Discriminator. Also, the document introduces a new
BGP Community, Standby PE, extending BGP Multicast VPN routing so
that a C-multicast route can be advertised toward a Standby Upstream
PE.
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 May 16, 2021.
Copyright Notice
Copyright (c) 2020 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
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(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 . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions used in this document . . . . . . . . . . . . . . 3
2.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2.3. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . 4
3. UMH Selection Based on Tunnel Status . . . . . . . . . . . . 5
3.1. Determining the Status of a Tunnel . . . . . . . . . . . 6
3.1.1. MVPN Tunnel Root Tracking . . . . . . . . . . . . . . 7
3.1.2. PE-P Upstream Link Status . . . . . . . . . . . . . . 7
3.1.3. P2MP RSVP-TE Tunnels . . . . . . . . . . . . . . . . 7
3.1.4. Leaf-initiated P-tunnels . . . . . . . . . . . . . . 8
3.1.5. (C-S, C-G) Counter Information . . . . . . . . . . . 8
3.1.6. BFD Discriminator Attribute . . . . . . . . . . . . . 8
3.1.7. Per PE-CE Link BFD Discriminator . . . . . . . . . . 12
4. Standby C-multicast Route . . . . . . . . . . . . . . . . . . 12
4.1. Downstream PE Behavior . . . . . . . . . . . . . . . . . 13
4.2. Upstream PE Behavior . . . . . . . . . . . . . . . . . . 14
4.3. Reachability Determination . . . . . . . . . . . . . . . 15
4.4. Inter-AS . . . . . . . . . . . . . . . . . . . . . . . . 15
4.4.1. Inter-AS Procedures for downstream PEs, ASBR Fast
Failover . . . . . . . . . . . . . . . . . . . . . . 16
4.4.2. Inter-AS Procedures for ASBRs . . . . . . . . . . . . 16
5. Hot Root Standby . . . . . . . . . . . . . . . . . . . . . . 17
6. Duplicate Packets . . . . . . . . . . . . . . . . . . . . . . 17
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
7.1. Standby PE Community . . . . . . . . . . . . . . . . . . 18
7.2. BFD Discriminator . . . . . . . . . . . . . . . . . . . . 18
7.3. BFD Discriminator Optional Sub-TLV Type . . . . . . . . . 19
8. Security Considerations . . . . . . . . . . . . . . . . . . . 20
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 20
10. Contributor Addresses . . . . . . . . . . . . . . . . . . . . 20
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 22
11.1. Normative References . . . . . . . . . . . . . . . . . . 22
11.2. Informative References . . . . . . . . . . . . . . . . . 23
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23
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1. Introduction
It is assumed that the reader is familiar with the workings of
multicast MPLS/BGP IP VPNs as described in [RFC6513] and [RFC6514].
In the context of multicast in BGP/MPLS VPNs [RFC6513], it is
desirable to provide mechanisms allowing fast recovery of
connectivity on different types of failures. This document addresses
failures of elements in the provider network that are upstream of PEs
connected to VPN sites with receivers.
Section 3 describes local procedures allowing an egress PE (a PE
connected to a receiver site) to take into account the status of
P-tunnels to determine the Upstream Multicast Hop (UMH) for a given
(C-S, C-G). One of the optional methods uses [RFC8562] and the new
BGP Attribute - BFD Discriminator. None of these methods provide a
"fast failover" solution when used alone, but can be used together
with the mechanism described in Section 4 for a "fast failover"
solution.
Section 4 describes an optional BGP extension, a new Standby PE
Community. that can speed up failover by not requiring any multicast
VPN (MVPN) routing message exchange at recovery time.
Section 5 describes a "hot leaf standby" mechanism that can be used
to improve failover time in MVPN. The approach combines mechanisms
defined in Section 3 and Section 4 has similarities with the solution
described in [RFC7431] to improve failover times when PIM routing is
used in a network given some topology and metric constraints.
The procedures described in this document are optional to enable an
operator to provide protection for multicast services in BGP/MPLS IP
VPNs. An operator would enable these mechanisms using a method
discussed in Section 3 in combination with the redundancy provided by
a standby PE connected to the source of the multicast flow, and it is
assumed that all PEs in the network would support these mechanisms
for the procedures to work. In the case that a BGP implementation
does not recognize or is configured to not support the extensions
defined in this document, it will continue to provide the multicast
service, as described in [RFC6513].
2. Conventions used in this document
2.1. 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
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14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2.2. Terminology
The terminology used in this document is the terminology defined in
[RFC6513] and [RFC6514].
The term 'upstream' (lower case) throughout this document refers to
links and nodes that are upstream to a PE connected to VPN sites with
receivers of a multicast flow.
The term 'Upstream' (capitalized) throughout this document refers to
a PE or an Autonomous System Border Router (ASBR) at which (S,G) or
(*,G) data packets enter the VPN backbone or the local AS when
traveling through the VPN backbone.
2.3. Acronyms
PMSI: P-Multicast Service Interface
I-PMSI: Inclusive PMSI
S-PMSI: Selective PMSI
x-PMSI: Either an I-PMSI or an S-PMSI
P-tunnel: Provider-Tunnels
UMH: Upstream Multicast Hop
VPN: Virtual Private Network
MVPN: Multicast VPN
RD: Route Distinguisher
RP: Rendezvous Point
NLRI: Network Layer Reachability Information
VRF: VPN Routing and Forwarding Table
MED: Multi-Exit Discriminator
P2MP: Point-to-Multipoint
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3. UMH Selection Based on Tunnel Status
Section 5.1 of [RFC6513] describes procedures used by a multicast VPN
downstream PE to determine the Upstream Multicast Hop (UMH) for a
given (C-S, C-G).
For a given downstream PE and a given VRF, the P-tunnel corresponding
to a given Upstream PE for a given (C-S, C-G) state is the S-PMSI
tunnel advertised by that Upstream PE for this (C-S, C-G) and
imported into that VRF, or if there isn't any such S-PMSI, the I-PMSI
tunnel advertised by that PE and imported into that VRF.
The procedure described here is an OPTIONAL procedure that is based
on a downstream PE taking into account the status of P-tunnels rooted
at each possible Upstream PE, for including or not including each
given PE in the list of candidate UMHs for a given (C-S, C-G) state.
If it is not possible to determine whether a P-tunnel's current
status is Up, the state shall be considered "not known to be Down",
and it may be treated as if it is Up so that attempts to use the
tunnel are acceptable. The result is that, if a P-tunnel is Down
(see Section 3.1), the PE that is the root of the P-tunnel will not
be considered for UMH selection. This will result in the downstream
PE failing over to use the next Upstream PE in the list of
candidates. Some downstream PEs could arrive at a different
conclusion regarding the tunnel's state because the failure impacts
only a subset of branches. Because of that, the procedures of
Section 9.1.1 of [RFC6513] are applicable when using I-PMSI
P-tunnels. That document is a foundation for this document, and its
processes all apply here. Section 9.1.1 mandates the use of specific
procedures for sending intra-AS I-PMSI A-D Routes.
There are three options specified in Section 5.1 of [RFC6513] for a
downstream PE to select an Upstream PE.
o The first two options select the Upstream PE from a candidate PE
set either based on an IP address or a hashing algorithm. When
used together with the optional procedure of considering the
P-tunnel status as in this document, a candidate Upstream PE is
included in the set if it either:
A. advertises an x-PMSI bound to a tunnel, where the specified
tunnel's state is not known to be Down, or,
B. does not advertise any x-PMSI applicable to the given (C-S,
C-G) but has associated a VRF Route Import BGP attribute to
the unicast VPN route for S. That is necessary to avoid
incorrectly invalidating a UMH PE that would use a policy
where no I-PMSI is advertised for a given VRF and where only
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S-PMSI are used. The S-PMSI can be advertised only after the
Upstream PE receives a C-multicast route for (C-S, C-G)/(C-*,
C-G) to be carried over the advertised S-PMSI.
If the resulting candidate set is empty, then the procedure is
repeated without considering the P-tunnel status.
o The third option uses the installed UMH Route (i.e., the "best"
route towards the C-root) as the Selected UMH Route, and its
originating PE is the selected Upstream PE. With the optional
procedure of considering P-tunnel status as in this document, the
Selected UMH Route is the best one among those whose originating
PE's P-tunnel is not "down". If that does not exist, the
installed UMH Route is selected regardless of the P-tunnel status.
3.1. Determining the Status of a Tunnel
Different factors can be considered to determine the "status" of a
P-tunnel and are described in the following sub-sections. The
optional procedures described in this section also handle the case
the downstream PEs do not all apply the same rules to define what the
status of a P-tunnel is (please see Section 6), and some of them will
produce a result that may be different for different downstream PEs.
Thus, the "status" of a P-tunnel in this section is not a
characteristic of the tunnel in itself, but is the tunnel status, as
seen from a particular downstream PE. Additionally, some of the
following methods determine the ability of a downstream PE to receive
traffic on the P-tunnel and not specifically on the status of the
P-tunnel itself. That could be referred to as "P-tunnel reception
status", but for simplicity, we will use the terminology of P-tunnel
"status" for all of these methods.
Depending on the criteria used to determine the status of a P-tunnel,
there may be an interaction with another resiliency mechanism used
for the P-tunnel itself, and the UMH update may happen immediately or
may need to be delayed. Each particular case is covered in each
separate sub-section below.
All methods described in this section may produce false-negative
state changes that can be the trigger for an unnecessary failover
negatively impacting the multicast service provided by the VPN. An
operator expected to consider the network environment and use
available controls of the mechanism used to determine the status of a
P-tunnel.
An implementation may support any combination of the methods
described in this section and provide a network operator with control
to choose which one to use in the particular deployment.
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3.1.1. MVPN Tunnel Root Tracking
A condition to consider that the status of a P-tunnel is Up is that
the root of the tunnel, as determined in the x-PMSI Tunnel attribute,
is reachable through unicast routing tables. In this case, the
downstream PE can immediately update its UMH when the reachability
condition changes.
That is similar to BGP next-hop tracking for VPN routes, except that
the address considered is not the BGP next-hop address, but the root
address in the x-PMSI Tunnel attribute.
If BGP next-hop tracking is done for VPN routes and the root address
of a given tunnel happens to be the same as the next-hop address in
the BGP A-D Route advertising the tunnel, then checking, in unicast
routing tables, whether the tunnel root is reachable, will be
unnecessary duplication and thus will not bring any specific benefit.
3.1.2. PE-P Upstream Link Status
A condition to consider a tunnel status as Up can be that the last-
hop link of the P-tunnel is Up. Conversely, if the last-hop link of
the P-tunnel is Down then this can be taken as an indication that the
P-tunnel is Down.
Using this method when a fast restoration mechanism (such as MPLS FRR
[RFC4090]) is in place for the link requires careful consideration
and coordination of defect detection intervals for the link and the
tunnel. In many cases, it is not practical to use both protection
methods at the same time because uncorrelated timers might cause
unnecessary switchovers and destabilize the network.
3.1.3. P2MP RSVP-TE Tunnels
For P-tunnels of type P2MP MPLS-TE, the status of the P-tunnel is
considered Up if the sub-LSP to this downstream PE is in the Up
state. The determination of whether a P2MP RSVP-TE LSP is in the Up
state requires Path and Resv state for the LSP and is based on
procedures specified in [RFC4875]. As a result, the downstream PE
can immediately update its UMH when the reachability condition
changes.
When using this method and if the signaling state for a P2MP TE LSP
is removed (e.g., if the ingress of the P2MP TE LSP sends a PathTear
message) or the P2MP TE LSP changes state from Up to Down as
determined by procedures in [RFC4875], the status of the
corresponding P-tunnel MUST be re-evaluated. If the P-tunnel
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transitions from Up to Down state, the Upstream PE that is the
ingress of the P-tunnel MUST NOT be considered a valid UMH.
3.1.4. Leaf-initiated P-tunnels
An Upstream PE SHOULD be removed from the UMH candidate list for a
given (C-S, C-G) if the P-tunnel (I-PMSI or S-PMSI) for this (S, G)
is leaf-triggered (PIM, mLDP), but for some reason, internal to the
protocol, the upstream one-hop branch of the tunnel from P to PE
cannot be built. As a result, the downstream PE can immediately
update its UMH when the reachability condition changes.
3.1.5. (C-S, C-G) Counter Information
In cases, where the downstream node can be configured so that the
maximum inter-packet time is known for all the multicast flows mapped
on a P-tunnel, the local per-(C-S, C-G) traffic counter information
for traffic received on this P-tunnel can be used to determine the
status of the P-tunnel.
When such a procedure is used, in the context where fast restoration
mechanisms are used for the P-tunnels, a configurable timer MUST be
set on the downstream PE to wait before updating the UMH, to let the
P-tunnel restoration mechanism to execute its actions. An
implementation SHOULD use three seconds as the default value for this
timer.
In cases where this mechanism is used in conjunction with the method
described in Section 5, no prior knowledge of the rate of the
multicast streams is required; downstream PEs can compare reception
on the two P-tunnels to determine when one of them is down.
3.1.6. BFD Discriminator Attribute
P-tunnel status may be derived from the status of a multipoint BFD
session [RFC8562] whose discriminator is advertised along with an
x-PMSI A-D Route.
This document defines the format and ways of using a new BGP
attribute called the "BFD Discriminator". It is an optional
transitive BGP attribute. An implementation that does not recognize
or is configured not to support this attribute MUST follow procedures
defined for optional transitive path attributes in Section 5 of
[RFC4271]. In Section 7.2, IANA is requested to allocate the
codepoint value (TBA2). The format of this attribute is shown in
Figure 1.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BFD Mode | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BFD Discriminator |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Optional TLVs ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Format of the BFD Discriminator Attribute
Where:
BFD Mode field is the one octet long. This specification defines
the P2MP BFD Session as value 1 Section 7.2.
Reserved field is three octets long, and the value MUST be zeroed
on transmission and ignored on receipt.
BFD Discriminator field is four octets long.
Optional TLVs is the optional variable-length field that MAY be
used in the BFD Discriminator attribute for future extensions.
TLVs MAY be included in a sequential or nested manner. To allow
for TLV nesting, it is advised to define a new TLV as a variable-
length object. Figure 2 presents the Optional TLV format TLV that
consists of:
* one octet-long field of TLV's Type value (Section 7.3)
* one octet-long field of the length of the Value field in octets
* variable length Value field.
The length of a TLV MUST be multiple of four octets.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Value ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Format of the Optional TLV
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The BFD Discriminator attribute MUST be considered malformed if its
length is not a non-zero multiple of four. If the attribute
considered malformed, the UPDATE message SHALL be handled using the
approach of Attribute Discard per [RFC7606].
3.1.6.1. Upstream PE Procedures
To enable downstream PEs to track the P-tunnel status using a point-
to-multipoint (P2MP) BFD session the Upstream PE:
o MUST initiate the BFD session and set bfd.SessionType =
MultipointHead as described in [RFC8562];
o MUST set the IP destination address of the inner IP header to one
of the internal loopback addresses from 127/8 range for IPv4 or
one of IPv4-mapped IPv6 addresses from ::ffff:127.0.0.0/104 range
for IPv6 when transmitting BFD Control packets;
o MUST use its IP address as the source IP address when transmitting
BFD Control packets;
o MUST include the BFD Discriminator attribute in the x-PMSI A-D
Route with the value set to My Discriminator value;
o MUST periodically transmit BFD Control packets over the x-PMSI
P-tunnel after the P-tunnel is considered established. Note that
the methods to declare a P-tunnel has been established are outside
the scope of this specification.
If the tracking of the P-tunnel by using a P2MP BFD session is
enabled after the x-PMSI A-D Route has been already advertised, the
x-PMSI A-D Route MUST be re-sent with precisely the same attributes
as before and the BFD Discriminator attribute included.
If the x-PMSI A-D Route is advertised with P-tunnel status tracked
using the P2MP BFD session and it is desired to stop tracking
P-tunnel status using BFD, then:
o x-PMSI A-D Route MUST be re-sent with precisely the same
attributes as before, but the BFD Discriminator attribute MUST be
excluded;
o the P2MP BFD session SHOULD be deleted.
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3.1.6.2. Downstream PE Procedures
Upon receiving the BFD Discriminator attribute in the x-PMSI A-D
Route, the downstream PE:
o MUST associate the received BFD Discriminator value with the
P-tunnel originating from the Upstream PE and the IP address of
the Upstream PE;
o MUST create a P2MP BFD session and set bfd.SessionType =
MultipointTail as described in [RFC8562];
o MUST use the source IP address of the BFD Control packet, the
value of the BFD Discriminator field, and the x-PMSI Tunnel
Identifier [RFC6514] the BFD Control packet was received to
properly demultiplex BFD sessions.
After the state of the P2MP BFD session is up, i.e., bfd.SessionState
== Up, the session state will then be used to track the health of the
P-tunnel.
According to [RFC8562], if the downstream PE receives Down or
AdminDown in the State field of the BFD Control packet or associated
with the BFD session Detection Timer expires, the BFD session is
down, i.e., bfd.SessionState == Down. When the BFD session state is
Down, then the P-tunnel associated with the BFD session MUST be
considered down. If the site that contains C-S is connected to two
or more PEs, a downstream PE will select one as its Primary Upstream
PE, while others are considered as Standby Upstream PEs. In such a
scenario, when the P-tunnel is considered down, the downstream PE MAY
initiate a switchover of the traffic from the Primary Upstream PE to
the Standby Upstream PE only if the Standby Upstream PE is deemed
available.
If the downstream PE's P-tunnel is already established when the
downstream PE receives the new x-PMSI A-D Route with BFD
Discriminator attribute, the downstream PE MUST associate the value
of BFD Discriminator field with the P-tunnel and follow procedures
listed above in this section if and only if the x-PMSI A-D Route was
properly processed as per [RFC6514], and the BFD Discriminator
attribute was validated.
If the downstream PE's P-tunnel is already established, its state
being monitored by the P2MP BFD session, and the downstream PE
receives the new x-PMSI A-D Route without the BFD Discriminator
attribute, and the x-PMSI A-D Route was processed without any error
as per the relevant specifications, the downstream PE:
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o MUST stop processing BFD Control packets for this P2MP BFD
session;
o SHOULD delete the P2MP BFD session associated with the P-tunnel;
o SHOULD NOT switch the traffic to the Standby Upstream PE.
3.1.7. Per PE-CE Link BFD Discriminator
The following approach is defined in response to the detection by the
Upstream PE of a PE-CE link failure. Even though the provider tunnel
is still up, it is desired for the downstream PEs to switch to a
backup Upstream PE. To achieve that, if the Upstream PE detects that
its PE-CE link fails, it SHOULD set the bfd.LocalDiag of the P2MP BFD
session to Concatenated Path Down and/or Reverse Concatenated Path
Down (per Section 6.8.17 [RFC5880]), unless it switches to a new PE-
CE link within the time of bfd.DesiredMinTxInterval for the P2MP BFD
session (in that case, the Upstream PE will start tracking the status
of the new PE-CE link). When a downstream PE receives that
bfd.LocalDiag code, it treats it as if the tunnel itself failed and
tries to switch to a backup PE.
4. Standby C-multicast Route
The procedures described below are limited to the case where the site
that contains C-S is connected to two or more PEs, though, to
simplify the description, the case of dual-homing is described. Such
a redundancy protection scheme, referred to as 1:N protection, is the
special case of M:N protection, where M working instances are sharing
protection of the N standby instances. In addition to a network
failure detection mechanism, the latter scheme requires using a
mechanism to coordinate the failover among working instances. For
that reason, M:N protection is outside the scope of this
specification.
The procedures described in this section require all the PEs of that
MVPN to follow the same UMH selection procedure, as specified in
[RFC6513], whether the PE selected based on its IP address, hashing
algorithm described in section 5.1.3 of [RFC6513], or Installed UMH
Route. The procedures assume that if a site of a given MVPN that
contains C-S is dual-homed to two PEs, then all the other sites of
that MVPN would have two unicast VPN routes (VPN-IPv4 or VPN-IPv6) to
C-S, each with its RD.
As long as C-S is reachable via both PEs, a given downstream PE will
select one of the PEs connected to C-S as its Upstream PE for C-S.
We will refer to the other PE connected to C-S as the "Standby
Upstream PE". Note that if the connectivity to C-S through the
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Primary Upstream PE becomes unavailable, then the PE will select the
Standby Upstream PE as its Upstream PE for C-S. When the Primary PE
later becomes available, then the PE will select the Primary Upstream
PE again as its Upstream PE. Such behavior is referred to as
"revertive" behavior and MUST be supported. Non-revertive behavior
refers to the behavior of continuing to select the backup PE as the
UMH even after the Primary has come up. This non-revertive behavior
MAY also be supported by an implementation and would be enabled
through some configuration.
For readability, in the following sub-sections, the procedures are
described for BGP C-multicast Source Tree Join routes, but they apply
equally to BGP C-multicast Shared Tree Join routes for the case where
the customer RP is dual-homed (substitute "C-RP" to "C-S").
4.1. Downstream PE Behavior
When a (downstream) PE connected to some site of an MVPN needs to
send a C-multicast route (C-S, C-G), then following the procedures
specified in Section 11.1 of [RFC6514], the PE sends the C-multicast
route with an RT that identifies the Upstream PE selected by the PE
originating the route. As long as C-S is reachable via the Primary
Upstream PE, the Upstream PE is the Primary Upstream PE. If C-S is
reachable only via the Standby Upstream PE, then the Upstream PE is
the Standby Upstream PE.
If C-S is reachable via both the Primary and the Standby Upstream PE,
then in addition to sending the C-multicast route with an RT that
identifies the Primary Upstream PE, the downstream PE also originates
and sends a C-multicast route with an RT that identifies the Standby
Upstream PE. The route that has the semantics of being a "standby"
C-multicast route is further called a "Standby BGP C-multicast
route", and is constructed as follows:
o the NLRI is constructed as the C-multicast route with an RT that
identifies the Primary Upstream PE, except that the RD is the same
as if the C-multicast route was built using the Standby Upstream
PE as the UMH (it will carry the RD associated to the unicast VPN
route advertised by the Standby Upstream PE for S and a Route
Target derived from the Standby Upstream PE's UMH route's VRF RT
Import EC);
o MUST carry the "Standby PE" BGP Community (this is a new BGP
Community. Section 7.1 requested IANA to allocate value TBA1).
The Local Preference attribute of the normal and the standby
C-multicast route needs to be adjusted. so that, if a BGP peer
receives two C-multicast routes with the same NLRI, one carrying the
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"Standby PE" community and the other one not carrying the "Standby
PE" community, then preference is given to the one not carrying the
"Standby PE" community. Such a situation can happen when, for
instance, due to transient unicast routing inconsistencies or lack of
support of the Standby PE community, two different downstream PEs
consider different Upstream PEs to be the primary one. In that case,
without any precaution taken, both Upstream PEs would process a
standby C-multicast route and possibly stop forwarding at the same
time. For this purpose, routes that carry the "Standby PE" BGP
Community MUST have the LOCAL_PREF attribute set to zero.
Note that, when a PE advertises such a Standby C-multicast join for a
(C-S, C-G) it MUST join the corresponding P-tunnel.
If at some later point, the PE determines that C-S is no longer
reachable through the Primary Upstream PE, the Standby Upstream PE
becomes the Upstream PE, and the PE re-sends the C-multicast route
with RT that identifies the Standby Upstream PE, except that now the
route does not carry the Standby PE BGP Community (which results in
replacing the old route with a new route, with the only difference
between these routes being the presence/absence of the Standby PE BGP
Community). The LOCAL_PREF attribute MUST be set to zero.
4.2. Upstream PE Behavior
When a PE receives a C-multicast route for a particular (C-S, C-G),
and the RT carried in the route results in importing the route into a
particular VRF on the PE, if the route carries the Standby PE BGP
Community, then the PE performs as follows:
when the PE determines (the use of the particular method to detect
the failure is outside the scope of this document) that C-S is not
reachable through some other PE, the PE SHOULD install VRF PIM
state corresponding to this Standby BGP C-multicast route (the
result will be that a PIM Join message will be sent to the CE
towards C-S, and that the PE will receive (C-S, C-G) traffic), and
the PE SHOULD forward (C-S, C-G) traffic received by the PE to
other PEs through a P-tunnel rooted at the PE.
Furthermore, irrespective of whether C-S carried in that route is
reachable through some other PE:
a) based on local policy, as soon as the PE receives this Standby BGP
C-multicast route, the PE MAY install VRF PIM state corresponding
to this BGP Source Tree Join route (the result will be that Join
messages will be sent to the CE toward C-S, and that the PE will
receive (C-S, C-G) traffic)
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b) based on local policy, as soon as the PE receives this Standby BGP
C-multicast route, the PE MAY forward (C-S, C-G) traffic to other
PEs through a P-tunnel independently of the reachability of C-S
through some other PE. [note that this implies also doing a)]
Doing neither a) or b) for a given (C-S, C-G) is called "cold root
standby".
Doing a) but not b) for a given (C-S, C-G) is called "warm root
standby".
Doing b) (which implies also doing a)) for a given (C-S, C-G) is
called "hot root standby".
Note that, if an Upstream PE uses an S-PMSI only policy, it shall
advertise an S-PMSI for a (C-S, C-G) as soon as it receives a
C-multicast route for (C-S, C-G), normal or Standby; i.e., it shall
not wait for receiving a non-Standby C-multicast route before
advertising the corresponding S-PMSI.
Section 9.3.2 of [RFC6514], describes the procedures of sending a
Source-Active A-D Route as a result of receiving the C-multicast
route. These procedures MUST be followed for both the normal and
Standby C-multicast routes.
4.3. Reachability Determination
The Standby Upstream PE can use the following information to
determine that C-S can or cannot be reached through the Primary
Upstream PE:
o presence/absence of a unicast VPN route toward C-S
o supposing that the Standby Upstream PE is the egress of the tunnel
rooted at the Primary Upstream PE, the Standby Upstream PE can
determine the reachability of C-S through the Primary Upstream PE
based on the status of this tunnel, determined thanks to the same
criteria as the ones described in Section 3.1 (without using the
UMH selection procedures of Section 3);
o other mechanisms MAY be used.
4.4. Inter-AS
If the non-segmented inter-AS approach is used, the procedures
described in Section 4.1 through Section 4.3 can be applied.
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When multicast VPNs are used in an inter-AS context with the
segmented inter-AS approach described in Section 9.2 of [RFC6514],
the procedures in this section can be applied.
A pre-requisite for the procedures described below to be applied for
a source of a given MVPN is:
o that any PE of this MVPN receives two or more Inter-AS I-PMSI A-D
Routes advertised by the AS of the source
o that these Inter-AS I-PMSI A-D Routes have distinct Route
Distinguishers (as described in item "(2)" of section 9.2 of
[RFC6514]).
As an example, these conditions will be satisfied when the source is
dual-homed to an AS that connects to the receiver AS through two ASBR
using auto-configured RDs.
4.4.1. Inter-AS Procedures for downstream PEs, ASBR Fast Failover
The following procedure is applied by downstream PEs of an AS, for a
source S in a remote AS.
Additionally to choosing an Inter-AS I-PMSI A-D Route advertised from
the AS of the source to construct a C-multicast route, as described
in section 11.1.3 [RFC6514], a downstream PE will choose a second
Inter-AS I-PMSI A-D Route advertised from the AS of the source and
use this route to construct and advertise a Standby C-multicast route
(C-multicast route carrying the Standby extended community), as
described in Section 4.1.
4.4.2. Inter-AS Procedures for ASBRs
When an Upstream ASBR receives a C-multicast route, and at least one
of the RTs of the route matches one of the ASBR Import RT, the ASBR,
that supports this specification, MUST try to locate an Inter-AS
I-PMSI A-D Route whose RD and Source AS respectively match the RD and
Source AS carried in the C-multicast route. If the match is found,
and the C-multicast route carries the Standby PE BGP Community, then
the ASBR MUST perform as follows:
o if the route was received over iBGP and its LOCAL_PREF attribute
is set to zero, then it MUST be re-advertised in eBGP with a MED
attribute (MULTI_EXIT_DISC) set to the highest possible value
(0xffff)
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o if the route was received over eBGP and its MED attribute set to
0xffff, then it MUST be re-advertised in iBGP with a LOCAL_PREF
attribute set to zero
Other ASBR procedures are applied without modification.
5. Hot Root Standby
The mechanisms defined in Section 4 and Section 3 can be used
together as follows.
The principle is that, for a given VRF (or possibly only for a given
(C-S, C-G):
o downstream PEs advertise a Standby BGP C-multicast route (based on
Section 4)
o Upstream PEs use the "hot standby" optional behavior and thus will
forward traffic for a given multicast state as soon as they have
whether a (primary) BGP C-multicast route or a Standby BGP
C-multicast route for that state (or both)
o downstream PEs accept traffic from the primary or standby tunnel,
based on the status of the tunnel (based on Section 3)
Other combinations of the mechanisms proposed in Section 4 and
Section 3 are for further study.
Note that the same level of protection would be achievable with a
simple C-multicast Source Tree Join route advertised to both the
primary and secondary Upstream PEs (carrying as Route Target extended
communities, the values of the VRF Route Import attribute of each VPN
route from each Upstream PEs). The advantage of using the Standby
semantic is that, supposing that downstream PEs always advertise a
Standby C-multicast route to the secondary Upstream PE, it allows to
choose the protection level through a change of configuration on the
secondary Upstream PE, without requiring any reconfiguration of all
the downstream PEs.
6. Duplicate Packets
Multicast VPN specifications [RFC6513] impose that a PE only forwards
to CEs the packets coming from the expected Upstream PE (Section 9.1
of [RFC6513]).
We draw the reader's attention to the fact that the respect of this
part of multicast VPN specifications is especially important when two
distinct Upstream PEs are susceptible to forward the same traffic on
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P-tunnels at the same time in the steady state. That will be the
case when "hot root standby" mode is used (Section 4), and which can
also be the case if procedures of Section 3 are used and a) the rules
determining the status of a tree are not the same on two distinct
downstream PEs or b) the rule determining the status of a tree
depends on conditions local to a PE (e.g., the PE-P upstream link
being up).
7. IANA Considerations
7.1. Standby PE Community
IANA is requested to allocate the BGP "Standby PE" community value
(TBA1) from the Border Gateway Protocol (BGP) Well-known Communities
registry using the First Come First Served registration policy.
7.2. BFD Discriminator
This document defines a new BGP optional transitive attribute, called
"BFD Discriminator". IANA is requested to allocate a codepoint
(TBA2) in the "BGP Path Attributes" registry to the BFD Discriminator
attribute.
IANA is requested to create a new BFD Mode sub-registry in the Border
Gateway Protocol (BGP) Parameters registry. The registration
policies, per [RFC8126], for this sub-registry are according to
Table 1.
+-----------+-------------------------+
| Value | Policy |
+-----------+-------------------------+
| 0- 175 | IETF Review |
| 176 - 249 | First Come First Served |
| 250 - 254 | Experimental Use |
| 255 | IETF Review |
+-----------+-------------------------+
Table 1: BFD Mode Sub-registry Registration Policies
IANA is requested to make initial assignments according to Table 2.
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+-----------+------------------+---------------+
| Value | Description | Reference |
+-----------+------------------+---------------+
| 0 | Reserved | This document |
| 1 | P2MP BFD Session | This document |
| 2- 175 | Unassigned | This document |
| 176 - 249 | Unassigned | This document |
| 250 - 254 | Experimental Use | This document |
| 255 | Reserved | This document |
+-----------+------------------+---------------+
Table 2: BFD Mode Sub-registry
7.3. BFD Discriminator Optional Sub-TLV Type
IANA is requested to create a new BFD Discriminator Optional sub-TLV
Type sub-registry in Border Gateway Protocol (BGP). The registration
policies, per [RFC8126], for this sub-registry are according to
Table 3.
+-----------+-------------------------+
| Value | Policy |
+-----------+-------------------------+
| 0- 175 | IETF Review |
| 176 - 249 | First Come First Served |
| 250 - 254 | Experimental Use |
| 255 | IETF Review |
+-----------+-------------------------+
Table 3: BFD Discriminator Optional Sub-TLV Type Sub-registry
Registration Policies
IANA is requested to make initial assignments according to Table 4.
+-----------+------------------+---------------+
| Value | Description | Reference |
+-----------+------------------+---------------+
| 0 | Reserved | This document |
| 1- 175 | Unassigned | This document |
| 176 - 249 | Unassigned | This document |
| 250 - 254 | Experimental Use | This document |
| 255 | Reserved | This document |
+-----------+------------------+---------------+
Table 4: BFD Discriminator Optional Sub-TLV Type Sub-registry
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8. Security Considerations
This document describes procedures based on [RFC6513] and [RFC6514]
and hence shares the security considerations respectively represented
in these specifications.
This document uses P2MP BFD, as defined in [RFC8562], which, in turn,
is based on [RFC5880]. Security considerations relevant to each
protocol are discussed in the respective protocol specifications. An
implementation that supports this specification MUST use a mechanism
to control the maximum number of P2MP BFD sessions that can be active
at the same time.
9. Acknowledgments
The authors want to thank Greg Reaume, Eric Rosen, Jeffrey Zhang,
Martin Vigoureux, Adrian Farrel, and Zheng (Sandy) Zhang for their
reviews, useful comments, and helpful suggestions.
10. Contributor Addresses
Below is a list of other contributing authors in alphabetical order:
Rahul Aggarwal
Arktan
Email: raggarwa_1@xxxxxxxxx
Nehal Bhau
Cisco
Email: NBhau@xxxxxxxxx
Clayton Hassen
Bell Canada
2955 Virtual Way
Vancouver
CANADA
Email: Clayton.Hassen@xxxxxxx
Wim Henderickx
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Nokia
Copernicuslaan 50
Antwerp 2018
Belgium
Email: wim.henderickx@xxxxxxxxx
Pradeep Jain
Nokia
701 E Middlefield Rd
Mountain View, CA 94043
USA
Email: pradeep.jain@xxxxxxxxx
Jayant Kotalwar
Nokia
701 E Middlefield Rd
Mountain View, CA 94043
USA
Email: Jayant.Kotalwar@xxxxxxxxx
Praveen Muley
Nokia
701 East Middlefield Rd
Mountain View, CA 94043
U.S.A.
Email: praveen.muley@xxxxxxxxx
Ray (Lei) Qiu
Juniper Networks
1194 North Mathilda Ave.
Sunnyvale, CA 94089
U.S.A.
Email: rqiu@xxxxxxxxxxx
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Yakov Rekhter
Juniper Networks
1194 North Mathilda Ave.
Sunnyvale, CA 94089
U.S.A.
Email: yakov@xxxxxxxxxxx
Kanwar Singh
Nokia
701 E Middlefield Rd
Mountain View, CA 94043
USA
Email: kanwar.singh@xxxxxxxxx
11. References
11.1. 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>.
[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271,
DOI 10.17487/RFC4271, January 2006,
<https://www.rfc-editor.org/info/rfc4271>.
[RFC4875] Aggarwal, R., Ed., Papadimitriou, D., Ed., and S.
Yasukawa, Ed., "Extensions to Resource Reservation
Protocol - Traffic Engineering (RSVP-TE) for Point-to-
Multipoint TE Label Switched Paths (LSPs)", RFC 4875,
DOI 10.17487/RFC4875, May 2007,
<https://www.rfc-editor.org/info/rfc4875>.
[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>.
[RFC6513] Rosen, E., Ed. and R. Aggarwal, Ed., "Multicast in MPLS/
BGP IP VPNs", RFC 6513, DOI 10.17487/RFC6513, February
2012, <https://www.rfc-editor.org/info/rfc6513>.
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[RFC6514] Aggarwal, R., Rosen, E., Morin, T., and Y. Rekhter, "BGP
Encodings and Procedures for Multicast in MPLS/BGP IP
VPNs", RFC 6514, DOI 10.17487/RFC6514, February 2012,
<https://www.rfc-editor.org/info/rfc6514>.
[RFC7606] Chen, E., Ed., Scudder, J., Ed., Mohapatra, P., and K.
Patel, "Revised Error Handling for BGP UPDATE Messages",
RFC 7606, DOI 10.17487/RFC7606, August 2015,
<https://www.rfc-editor.org/info/rfc7606>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[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>.
[RFC8562] Katz, D., Ward, D., Pallagatti, S., Ed., and G. Mirsky,
Ed., "Bidirectional Forwarding Detection (BFD) for
Multipoint Networks", RFC 8562, DOI 10.17487/RFC8562,
April 2019, <https://www.rfc-editor.org/info/rfc8562>.
11.2. Informative References
[RFC4090] Pan, P., Ed., Swallow, G., Ed., and A. Atlas, Ed., "Fast
Reroute Extensions to RSVP-TE for LSP Tunnels", RFC 4090,
DOI 10.17487/RFC4090, May 2005,
<https://www.rfc-editor.org/info/rfc4090>.
[RFC7431] Karan, A., Filsfils, C., Wijnands, IJ., Ed., and B.
Decraene, "Multicast-Only Fast Reroute", RFC 7431,
DOI 10.17487/RFC7431, August 2015,
<https://www.rfc-editor.org/info/rfc7431>.
Authors' Addresses
Thomas Morin (editor)
Orange
2, avenue Pierre Marzin
Lannion 22307
France
Email: thomas.morin@xxxxxxxxxxxxxxxxxx
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Robert Kebler (editor)
Juniper Networks
1194 North Mathilda Ave.
Sunnyvale, CA 94089
U.S.A.
Email: rkebler@xxxxxxxxxxx
Greg Mirsky (editor)
ZTE Corp.
Email: gregimirsky@xxxxxxxxx
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