Network Working Group                             Gargi Nalawade
Internet Draft                                 Arjun Sreekantiah
Expires: April 2006 Cisco Systems

                                MDT SAFI

1. Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
   aware will be disclosed, in accordance with Section 6 of BCP 79.

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2. Copyright Notice

   Copyright (C) The Internet Society (2005).  All Rights Reserved.

3. Abstract

   There is a need for transporting Multicast Tunnel attributes within
   and across Autonomous Systems. This draft defines a new Address-
   Family that can be used to do the distribution.

4. Introduction

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   Two end-points of a Multicast Tunnel need to know the end-point
   information and its binding to a network address and the Multicast
   Tunnel used for the respective VRF at the remote PE. Normally, Tunnel
   endpoint addresses can be statically configured. But in case of a
   large network with large number of VPNs where there may be a need for
   a large number of endpoints and a large number of VRFs, the amount of
   information that needs to be exchanged and maintained between PEs for
   Multicast Tunnels for VPNs, is quite large. It therefore needs a
   mechanism that can maintain and support Multicast Tunnel based VPNs
   in a flexible, scalable manner. Also, in inter-AS and inter- provider
   scenarios, this mechanism needs to be supported across autonomous
   systems and provider domains.


   A new Subsequent-Address Family called the MDT SAFI is being defined.
   The NLRI for this SAFI, will contain the address of the nexthop which
   will be used by the multicast source PE to send the PIM Join for the
   default MDT address to.

   The NLRI format is 8-byte-RD:IPv4-address followed by the MDT group
   address.  i.e. The MP_REACH attribute for this SAFI will contain one
   or more tuples of the following form :

          |                               |
          |  RD:IPv4-address (12 octets)  |
          |                               |
          |  MDT Group-address (4 octets) |

   where :

   Route-Distinguisher : is the RD of the VRF to which this MDT
   attribute belongs.

   MDT Group Address : is the Group-address of the MDT-Group that a VRF
   is associated to. This can be variable length. But for

   IPV4 addresses - this will be 4 octets.

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6. The Connector Attribute

   An Optional Transitive Connector attribute [BGP-CONN] will be used to
   transport the address of the originating PE router unchanged to the
   remote PE router which is participating in the same MVPN.

   The format of this attribute is a 2-octet Type field followed by the
   Value. Type 1 of this attribute defines that this is an IPv4 unicast
   nexthop set by the PE which advertises the CE-learnt prefixes to its

   The attribute contains one or more tuples of the form :

          |                              |
          |  Type (2 octets)             |
          |                              |
          |  Value (Variable)            |
          |                              |

   where :

   Type : is the Type of the data contained in this TLV.

   Value : is a variable length field as defined by the Type.

   When the Type is 1, the value will contain the IPv4 address of the PE
   sourcing the CE-learnt VPNv4 prefixes. This would be the same address
   this PE uses to set itself as the nexthop.  This attribute will
   accompany the VPNv4 prefix advertisement.

7. Capability Advertisement

   A BGP speaker that wishes to exchange the MDT SAFI, MUST use the
   MP_EXT Capability Code as defined in [BGP-MP], to advertise the
   corresponding (AFI, SAFI) pair.

   A BGP speaker MAY participate in the distribution of MDT information.

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8. Operation

   A BGP Speaker that receives the Capability for the MDT SAFI, MAY
   advertise the MDT SAFI prefixes to that peer. The prefixes in the MDT
   SAFI are populated by the PEs that advertise their CE-learnt

9. Applicability Statement

   Multicast Tunnels are built between Provider Edge (PE) routers to
   allow multicast communication between different site's of a VPN. The
   MT tunnel has a destination MDT group address that is unique to the
   VPN. All routers that act as PE's and are configured for a specific
   VPN join the VPN MDT multicast group in the backbone of the provider
   network to be able to receive each others packets.  Each router is
   also a sender to the MDT group. In PIM SSM mode, the following
   procedure is followed.

   A Multicast tunnel is setup between the PEs in one or more VPN-
   Providers networks. Over the Multicast tunnel we create PIM
   neighbor's. The IP address of the PIM neighbor that is seen over the
   Multicast tunnel depends on the configured address of the Tunnel
   endpoint. This can either be an unnumbered address from a different
   interface or a configured address on the Tunnel itself. The PE router
   that does an RPF check on a VPN source can find which Tunnel the
   source is on, but may not know what PIM neighbor to target on that
   tunnel.  Therefore we need a way to connect the BGP VPNv4 prefix to
   the PIM neighbor on the tunnel to allow the RPF check to succeed.

   Suppose we want to join to a source that is behind another VPN site.
   We do an RPF lookup on the source address in the VPNv4 unicast table
   on this PE. The RPF lookup will return a connected next-hop and
   interface to use to reach the source. The returned next-hop may not
   be the neighbor on the Multicast tunnel. This can be due to the
   next-hop being rewritten by BGP Route Reflectors (RR) or crossing
   AS's. Therefore we don't know which PIM neighbor to target as
   upstream neighbor in the PIM join.

   defines a new attribute called the BGP Connector attribute. This We
   propose sending the Originating PE's IP address through the BGP
   Connector Attribute. It will be sent as the value field when the BGP
   Connector attribute contains Type 1. This is the Multicast Tunnel's
   IP address which is used to establish the PIM neighbor relationship
   on the Multicast tunnel. This attribute is attached to all the BGP
   VPNv4 prefixes used for reaching to multicast sources in the
   Customer's network. The PE router that was able to successfully RPF
   on a BGP VPNv4 prefix will use the IP address learned from the
   connected attribute to find the PIM neighbor on the Multicast tunnel.

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10. Security Considerations

   This extension to BGP does not change the underlying security issues.

11. Acknowledgements

   The authors would like to thank  IJsbrand Wijnands for his contr-
   ibution towards the Connector Attribute needed for the IPv4-MDT SAFI.
   The authors would also like to thank Shyam Suri, Ruchi Kapoor, Shyam
   Suri, Yiqun Cai, Dan Tappan, Jennifer Li, Yi Chou, Arjen Boers for
   their comments and contributions. We would also like to thank Bhavani
   Parise for his review and comments.

12. Normative References

   [BGP-4]  Rekhter, Y. and T. Li (editors), "A Border Gateway Protocol
   4 (BGP-4)", Internet Draft draft-ietf-idr-bgp4-26.txt, April 2005.

   [BGP-CAP] Chandra, R., Scudder, J., "Capabilities Advertisement with
   BGP-4", draft-ietf-idr-rfc2842bis-02.txt, April 2002.

   [BGP-SSA] Kapoor R., Nalawade G., “BGPv4 SAFI-Specific Attribute”,
   draft-nalawade-kapoor-bgp-ssa-00.txt, January 2006.

   [MULTI-BGP] Bates et al, Multiprotocol Extensions for BGP-4, draft-
   ietf-idr-rfc2858bis-02.txt, work in progress.

   [BGP-CONN] Nalawade Gargi, Kapoor Ruchi "BGPv4 Connector Attribute",
   OCT-05, <draft-nalawade-bgp-connector-00.txt>, work in progress.

13. Author's Addresses

   Gargi Nalawade
   170 Tasman Drive
   San Jose, CA, 95134

   Arjun Sreekantiah
   170 Tasman Drive
   San Jose, CA, 95134

14. Intellectual Property Statement

   Cisco Systems may seek patent or other intellectual property
   protection for some of all of the technologies disclosed in this
   document. If any standards arising from this document are or become
   protected by one or more patents assigned to Cisco Systems, Cisco

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   intends to disclose those patents and license them on reasonable
   and non-discriminatory terms.

15. Full Copyright Statement

   Copyright (C) The Internet Society (2005).  All Rights Reserved.

   This document is subject to the rights, licenses and restrictions
   contained in BCP 78, and except as set forth therein, the authors
   retain all their rights.

   This document and the information contained herein are provided on

16. Expiration Date

   This memo is filed as <draft-nalawade-idr-mdt-safi-03.txt>, and
   expires April, 2006.

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