Network Working Group P. Mohapatra
Internet-Draft Sproute Networks
Intended status: Standards Track A. Sreekantiah
Expires: March 16, 2018 Cisco Systems
K. Patel
Arrcus Inc
B. Pithawala
Cisco Systems
A. Lo
Arista Networks
September 12, 2017

Automatic Route Target Filtering for legacy PEs


This document describes a simple procedure that allows "legacy" BGP speakers to exchange route target membership information in BGP without using mechanisms specified in [RFC4684]. The intention of the proposed technique is to help in partial deployment scenarios and is not meant to replace [RFC4684].

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Table of Contents

1. Introduction

[RFC4684] provides a powerful and general means for BGP speakers to exchange and propagate Route Target reachability information and constrain VPN route distribution to achieve high scale. However, it requires that all the BGP speakers in the network are upgraded to support this functionality. For example, in a network with route reflectors (RR), if one PE client in the cluster doesn't support constrained distribution, the cluster degenerates into storing and processing all the VPN routes. The route reflectors need to request and store all the network routes since they do not receive route target membership information from the legacy PEs. The RR will also generate all those routes to the legacy PEs and the legacy PEs will end up filtering the routes and store the subset of VPN routes that are of interest.

This document specifies a mechanism for such legacy PE devices using existing configuration and toolset to provide similar benefits as [RFC4684]. At the same time, it is backward-compatible with the procedures defined in [RFC4684]. It also allows graceful upgrade of the legacy router to be [RFC4684] capable.

1.1. Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119.

2. Basic Idea

The basic idea is to make use of VPN unicast route exchange from the legacy PEs to a new BGP speaker (e.g. an RR) to signal RT membership. The legacy PEs announce a set of "special" routes with mapped RTs to the RR along with a standard community (defined in this document). The presence of the community triggers the RR to extract the RTs and build RT membership information.

3. Detailed Operation

3.1. Legacy PE Behavior

    0                   1              0                   1
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      0x00     |     0x02      |   |      0x01     |     0x02      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |2B AS                          |   |2B AS => IP(high)              |
   |Local Admin(high)              |   |Local Admin(high) => IP(low)   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Local Admin(low)               |   |Local Admin(low) => Local Admin|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    0                   1              0                   1
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      0x01     |     0x02      |   |      0x02     |     0x02      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |IP(high)                       |   |IP(high) => 4B AS(high)        |
   |IP(low)                        |   |IP(low) => 4B AS(low)          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Local Admin                    |   |Local Admin => Local Admin     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    0                   1              0                   1
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      0x02     |     0x02      |   |      0x00     |     0x02      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |4B AS(high)                    |   |4B AS(high) => 2B AS           |
   |4B AS(low)                     |   |4B AS(low) => Local Admin(high)|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Local Admin                    |   |Local Admin => Local Admin(low)|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


The following simple steps are performed on the legacy PE device:

3.2. RR Behavior

Upon receiving the "route-filter" routes, the BGP speaker does its usual processing to store them in its local RIB. It recognizes them as route-filter routes based on the association of the new standard community as defined in this document. If required (as indicated by the community value), it translates the attached route-target extended communities (TRT) to equivalent import route-targets (IRT). Finally it creates the route-target filter list for each legacy client by collecting the entire set of route targets. From this point onwards, the behavior is similar to that defined in [RFC4684]. The RR does not propagate the routes further because of their association with NO_ADVERTISE community. Also the VPN EoR that is sent by the legacy PE should also be used as an indication that the legacy PE is done sending the route-filter information as per the procedures defined in [RFC4684] for implementing a EoR mechanism to signal the completion of initial RT membership exchange.

3.2.1. Generating Route Target Membership NLRIs for the legacy PE clients

The RR MAY also translate the received extended communities from legacy clients into route target membership NLRIs as if it had received those NLRIs from the client itself. This is useful for further propagation of the NLRIs to rest of the network to create RT membership flooding graph. When the route_filter routes are received with same RD (from all legacy PE speakers), processing of the paths to generate equivalent NLRIs becomes fairly easy.

4. ROUTE_FILTER Community

   |          Community         | Meaning                              |
   |       ROUTE_FILTER_v4      | RTs are attached as-is for VPNv4     |
   |                            | route filtering                      |
   |             ...            | ...                                  |
   |       ROUTE_FILTER_v6      | RTs are attached as-is for VPNv6     |
   |                            | route filtering                      |
   |             ...            | ...                                  |
   | ROUTE_FILTER_TRANSLATED_v4 | Translated RTs are attached for      |
   |                            | VPNv4 route filtering                |
   |             ...            | ...                                  |
   | ROUTE_FILTER_TRANSLATED_v6 | Translated RTs are attached for      |
   |                            | VPNv6 route filtering                |


This memo defines four BGP communities that are attached to BGP UPDATE messages at the legacy PE devices and processed by the route reflectors as defined above. They are as follows: [RFC4684] to build combination route-filters for VPN AFs and AF specific route-filters defined in [I-D.keyur-bgp-af-specific-rt-constrain]. If this is the case, then subsequent receipt of any "route-filter" routes with AF specific communities (ROUTE_FILTER_v6, ROUTE_FILTER_TRANSLATED_v6) will override the default filters sent with ROUTE_FILTER_v4 or ROUTE_FILTER_TRANSLATED_v4 for the VPNv6 AFI when support for the AF specific communities exists. Suggested values for ROUTE_FILTER_v4 and ROUTE_FILTER_TRANSLATED_v4 are 0xFFFF0002 (65535:2) and 0xFFFF0003 (65535:3) respectively

5. Deployment Considerations

When both the legacy PE and the RR support extended community based Outbound Route Filtering as in [I-D.chen-bgp-ext-community-orf] this may be used as a alternate solution for the legacy PE to signal RT membership information, in order to realize the same benefits as [RFC4684]. Also extended community ORF can be used amongst the RRs in lieu of [RFC4684] to realize similar benefits.

6. Contributors

Significant contributions were made by Stephane Litkowski, Luis M Tomotaki and James Uttaro which the authors would like to acknowledge.

7. Acknowledgments

The authors would like to thank Rob Shakir for his review and comments.

8. IANA Considerations

IANA shall assign new code points from BGP first-come first-serve communities for the four communities as listed in Section 4.

9. Security Considerations

There are no additional security risks introduced by this design.

10. References

10.1. 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.
[RFC4271] Rekhter, Y., Li, T. and S. Hares, "A Border Gateway Protocol 4 (BGP-4)", RFC 4271, DOI 10.17487/RFC4271, January 2006.
[RFC4360] Sangli, S., Tappan, D. and Y. Rekhter, "BGP Extended Communities Attribute", RFC 4360, DOI 10.17487/RFC4360, February 2006.
[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February 2006.
[RFC4684] Marques, P., Bonica, R., Fang, L., Martini, L., Raszuk, R., Patel, K. and J. Guichard, "Constrained Route Distribution for Border Gateway Protocol/MultiProtocol Label Switching (BGP/MPLS) Internet Protocol (IP) Virtual Private Networks (VPNs)", RFC 4684, DOI 10.17487/RFC4684, November 2006.

10.2. Informational References

[I-D.chen-bgp-ext-community-orf] Chen, E., Lo, A. and K. Patel, "Extended Community Based Outbound Route Filter for BGP-4", Internet-Draft draft-chen-bgp-ext-community-orf-02, December 2011.
[I-D.keyur-bgp-af-specific-rt-constrain] Patel, K., Raszuk, R., Djernaes, M., Dong, J. and M. Chen, "IPv6 AF Extensions for Route Target Distribution", Internet-Draft draft-keyur-bgp-af-specific-rt-constrain-01, March 2011.

Authors' Addresses

Pradosh Mohapatra Sproute Networks EMail:
Arjun Sreekantiah Cisco Systems 170 W. Tasman Drive San Jose, CA 95134 USA EMail:
Keyur Patel Arrcus Inc EMail:
Burjiz Pithawala Cisco Systems 170 W. Tasman Drive San Jose, CA 95134 USA EMail:
Alton Lo Arista Networks 5470 Great America Parkway Santa Clara, CA 95054 USA EMail: