Internet DRAFT - draft-ietf-pim-explicit-rpf-vector
draft-ietf-pim-explicit-rpf-vector
Network Working Group J. Asghar
Internet-Draft IJ. Wijnands, Ed.
Intended status: Standards Track S. Krishnaswamy
Expires: October 28, 2016 A. Karan
Cisco Systems
V. Arya
DIRECTV Inc.
April 26, 2016
Explicit RPF Vector
draft-ietf-pim-explicit-rpf-vector-09.txt
Abstract
The PIM Reverse Path Forwarding (RPF) Vector TLV defined in RFC 5496
can be included in a PIM Join Attribute such that the RPF neighbor is
selected based on the unicast reachability of the RPF Vector instead
of the Source or Randezvous Point associated with the multicast tree.
This document defines a new RPF Vector Attribute type such that an
explicit RPF neighbor list can be encoded in the PIM Join Attribute,
bypassing the unicast route lookup.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on October 28, 2016.
Copyright Notice
Copyright (c) 2016 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Specification of Requirements . . . . . . . . . . . . . . . . 3
3. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Use of the PIM Explicit RPF Vector . . . . . . . . . . . . . 4
5. Explicit RPF Vector Attribute TLV Format . . . . . . . . . . 4
6. Mixed Vector Processing . . . . . . . . . . . . . . . . . . . 5
7. Conflicting RPF Vectors . . . . . . . . . . . . . . . . . . . 5
8. PIM Asserts . . . . . . . . . . . . . . . . . . . . . . . . . 6
9. Join Suppression . . . . . . . . . . . . . . . . . . . . . . 6
10. Unsupported Explicit Vector Handling . . . . . . . . . . . . 6
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
12. Security Considerations . . . . . . . . . . . . . . . . . . . 7
13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 7
14. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
14.1. Normative References . . . . . . . . . . . . . . . . . . 7
14.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
The procedures in [RFC5496] define how a RPF vector can be used to
influence the path selection in the absence of a route to the source.
The same procedures can be used to override a route to the source
when it exists. It is possible to include multiple RPF vectors in
the list where each router along the path will perform a unicast
route lookup on the first vector in the attribute list. Once the
router owning the address of the RPF vector is reached, following the
procedures in [RFC5496], the RPF vector will be removed from the
attribute list. This will result in a 'loosely' routed path that
still depends on unicast reachability to the RPF vector(s).
In some scenarios the network adminstrators don't want to rely on the
unicast reachability to the RPF vector address and want to build a
path strictly based on the RPF vectors. In that case the RPF vectors
represent a list of directly connected PIM neighbors along the path.
For these vectors the router would not do a route lookup in the
unicast routing table. These vectors are referred to as 'Explicit'
RPF Vector addresses. If a router receiving an Explicit RPF Vector
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does not have a PIM neighbor matching the Explicit RPF Vector
address, it does not fall back to loosely routing the join. Instead,
it could process the packet and store the RPF Vector list so that the
PIM join can be sent out as soon as the neighbor comes up. Since the
behavior of the Explicit RPF Vector differs from the loose RPF vector
as defined [RFC5496], a new attribute called the Explicit RPF Vector
is defined.
This document defines a new TLV in the PIM Join Attribute message
[RFC5384] for specifying the explicit path.
2. Specification of Requirements
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
3. Motivation
Some broadcast video transport networks use a multicast PIM Live-Live
resiliency model for video delivery based on PIM SSM or PIM ASM.
Live-Live implies using 2 active spatially diverse multicast trees to
transport video flows from root to leaf multicast routers. The leaf
multicast router receives 2 copies from the PIM multicast core and
will replicate 1 copy towards the receivers [RFC7431].
One of the requirements of the PIM Live-Live resiliency model is to
ensure path-diversity of the 2 active PIM trees in the core such that
they do not intersect to avoid a single point of failure. IGP routed
RPF paths of 2 PIM trees could be routed over the same transit router
and create a single point of failure. It is useful to have a way to
specify the explicit path along which the PIM join is propagated.
How the Explicit RPF Vector list is determined is outside the scope
of this document. For example, it may either be manually configured
by the network operator or procedures may be implemented on the
egress router to dynamically calculate the vector list based on a
link state database protocol, like OSPF or IS-IS.
Due to the fact that the leaf router receives two copies of the
multicast stream via two diverse paths, there is no need for PIM to
repair the broken path immediately. It is up to the egress router to
either wait for the broken path to be repaired or build a new
explicit path using a new RPF vector list. Which method is applied
depends very much on how the vector list was determined initially.
Double failures are not considered and are outside the scope of this
document.
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This document describes the procedures to carry Explicit RPF vectors
in PIM. It is up to the mechanism(s) that produce the Explicit RPF
Vectors to ensure they are correct. Existing mechanisms like
[I-D.ietf-mboned-mtrace-v2] may be used to verify how the PIM tree
was build.
4. Use of the PIM Explicit RPF Vector
Figure 1 provides an example multicast join path
R4->R3->R6->R5->R2->R1, where the multicast join is explicitly routed
to the source hop-by-hop using the Explicit RPF Vector list. When
R5-R6 link fails the join will NOT take an alternate path.
[S]---(R1)--(R2)---(R3)--(R4)---[R]
<--- | | ---
| | | |
| (R5)---(R6) |
- (S,G) Join -
| |
| |
(R7)---(R8)
Figure 1
In comparison, when [RFC5496] procedures are used, if R5-R6 link
fails then the join may be re-routed using R6-R8-R7 path to reach R5.
5. Explicit RPF Vector Attribute TLV Format
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|F|E| Type | Length | Value
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-.......
Figure 2
F bit: The F bit MUST be set to 0. Otherwise there could be loops.
E bit: End of Attributes. If this bit is set then this is the last
TLV specified in the list.
Type: The Vector Attribute type is TBD1.
Length: Length depending on the Address Family (IPv4 or IPv6) of the
Encoded-Unicast address.
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Value: Encoded-Unicast address. This SHOULD be a valid IPv4 or IPv6
address of an upstream router.
6. Mixed Vector Processing
Explicit RPF Vector attribute does not impact or restrict the
functionality of other RPF vector attributes in a PIM join. It is
possible to mix vectors of different types, such that some part of
the tree is explicit and other parts are loosely routed. RPF vectors
are processed in the order in which they are specified.
7. Conflicting RPF Vectors
It is possible that a PIM router has multiple downstream neighbors.
If for the same multicast route there is an inconsistency between the
Explicit RPF Vector lists provided by the downstream PIM neighbor,
the procedures as documented in section 3.3.3 [RFC5384] apply.
The conflict resolution procedures in section 3.3.3 [RFC5384] only
apply to attributes of the same Join Attribute type. Join Attributes
that have a different type can't be compared because the content of
the Join Attribute may have a totally different meaning and/or
encoding. This may cause a problem if a mix of Explicit RPF Vectors
(this document) and 'loose' RPF vectors [RFC5496] is received from
two or more downstream routers. The order in which the RPF vectors
are encoded may be different and/or the combination of RPF vectors
may be inconsistent. The procedures in section 3.3.3 [RFC5384] would
not resolve the conflict. The following procedures MUST be applied
to deal with this scenario.
When a PIM Join with Join Attribute list is received from a
downstream neighbor, the router MUST verify that the order in which
the RPF Vector types appear in the PIM Join Attribute list matches
what is stored as the Join Attribute list for reaching the Source or
Randezvous point listed in the PIM Join. Once it is determined that
the RPF Vector types on the stack are equal, the content of the RPF
Vectors MUST be compared ([RFC5384]). If it is determined that there
is either a conflict with RPF Vector types or the RPF Vector content,
the router uses the RPF Vector stack from the PIM adjacency with
numerically smallest IP address. In the case of IPv6, the link local
address will be used. When two neighbors have the same IP address,
either for IPv4 or IPv6, the interface index MUST be used as a tie
breaker. It's RECOMMENDED that the router doing the conflict
resolution log a message.
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8. PIM Asserts
Section 3.3.3 of [RFC5496] specifies the procedures for how to deal
with PIM asserts when RPF vectors are used. The same procedures
apply to the Explicit RPF Vector. There is minor behavioral
difference, the route metric that is included in the PIM Assert
should be the route metric of the first Explicit RPF vector address
in the list. However, the first Explicit vector should always be
directly connected, so the Metric may likely be zero. The Metric
will therefore not be a tie breaker in the PIM Assert selection
procedure.
9. Join Suppression
Section 3.3.4 of [RFC5496] specifies the procedures how to apply join
suppression when an RPF Vector attribute is included in the PIM join.
The same procedure applies to the Explicit RPF Vector attribute. The
procedure MUST match against all the Explicit RPF Vectors in the PIM
join before a PIM join can be suppressed.
10. Unsupported Explicit Vector Handling
The F bit MUST be set to 0 in all Explicit RPF vectors in case the
upstream router receiving the join does not support the TLV. As
described in section 3.3.2 of [RFC5384], routers that do not
understand the type of a particular attribute that has the F bit
clear will discard it and continue to process the join.
This processing is particularly important when the routers that do
not support the Explicit RPF TLV are identified as hops in the
explicit RPF list, because failing to remove the RPF vectors could
cause upstream routers to send the join back toward these routers
causing loops.
As the administrator is manually specifying the path that the joins
need to be sent on, it is recommended that the administrator computes
the path to include routers that support explcit vector and check
that the state is created correctly on each router along the path.
Tools like mtrace can be used for debugging and to ensure that the
join state is setup correctly.
11. IANA Considerations
A new attribute (TBD1) type from the "PIM Join Attribute Types"
registry needs to be assigned by IANA for the Explicit RPF Vector
attribute. The proposed value 4.
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12. Security Considerations
Security of the Explicit RPF Vector Attribute is only guaranteed by
the security of the PIM packet, so the security considerations for
PIM Join packets as described in PIM-SM [I-D.ietf-pim-rfc4601bis]
apply here. A malicious downstream node can attempt a denial of
service attack by sending PIM Join packets with invalid addresses
listed in the RPF vector stack with an intent to stop the propogation
of the joins to the correct upstream node. Another denial of service
attack would be a malicious downstream node targeting all joins to a
specific node with an intent to overload the bandwidth on that node
by making it responsible for forwarding multicast traffic for more
streams that it can handle. Inorder to minimize the risk of a denial
of service attacks from forged PIM join packets with explicit RPF
vector stack, it should be used within a single trusted management
domain.
If a router finds that it cannot use the vector list due to the next
hop router not being a PIM neighbor, it may log an error. Also if a
router is receiving two conflicting vectors it may log an error. It
is upto the mechanisms that produced the Explicit RPF vector to
ensure that the the PIM tree is built correctly and to monitor any
error logs.
13. Acknowledgments
The authors would like to thank Vatsa Kumar, Nagendra Kumar and
Bharat Joshi for the comments on the document.
14. References
14.1. Normative References
[I-D.ietf-pim-rfc4601bis]
Fenner, B., Handley, M., Holbrook, H., Kouvelas, I.,
Parekh, R., Zhang, J., and L. Zheng, "Protocol Independent
Multicast - Sparse Mode (PIM-SM): Protocol Specification
(Revised)", draft-ietf-pim-rfc4601bis-06 (work in
progress), August 2015.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
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[RFC5384] Boers, A., Wijnands, I., and E. Rosen, "The Protocol
Independent Multicast (PIM) Join Attribute Format",
RFC 5384, DOI 10.17487/RFC5384, November 2008,
<http://www.rfc-editor.org/info/rfc5384>.
[RFC5496] Wijnands, IJ., Boers, A., and E. Rosen, "The Reverse Path
Forwarding (RPF) Vector TLV", RFC 5496,
DOI 10.17487/RFC5496, March 2009,
<http://www.rfc-editor.org/info/rfc5496>.
14.2. Informative References
[I-D.ietf-mboned-mtrace-v2]
Asaeda, H., Meyer, K., and W. Lee, "Mtrace Version 2:
Traceroute Facility for IP Multicast", draft-ietf-mboned-
mtrace-v2-12 (work in progress), October 2015.
[RFC7431] Karan, A., Filsfils, C., Wijnands, IJ., Ed., and B.
Decraene, "Multicast-Only Fast Reroute", RFC 7431,
DOI 10.17487/RFC7431, August 2015,
<http://www.rfc-editor.org/info/rfc7431>.
Authors' Addresses
Javed Asghar
Cisco Systems
725, Alder Drive
Milpitas CA 95035
USA
Email: jasghar@cisco.com
IJsbrand Wijnands (editor)
Cisco Systems
De Kleetlaan 6a
Diegem 1831
Belgium
Email: ice@cisco.com
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Sowmya Krishnaswamy
Cisco Systems
3750 Cisco Way
San Jose CA 95134
USA
Email: sowkrish@cisco.com
Apoorva Karan
Cisco Systems
3750 Cisco Way
San Jose CA 95134
USA
Email: apoorva@cisco.com
Vishal Arya
DIRECTV Inc.
2230 E Imperial Hwy
El Segundo CA 90245
USA
Email: varya@directv.com
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