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Implementing BGP on Cisco IOS XR Software
How to Implement BGP on Cisco IOS XR Software
RC-42
Cisco IOS XR Routing Configuration Guide
OL-14356-01
When an MVPN-specific default MDT group is configured on PE1, PIM creates a virtual MDT tunnel
interface with the tunnel source address the same as the BGP local peering address. This MDT interface
is used by PIM to send VPN packets to the provider network and to receive VPN packets from the
provider network. PIM also exchanges control messages over this MDT interface.
Each time a default MDT group is configured for a specific VRF, BGP builds an MDT SAFI update, with
network layer reachability information (NLRI) containing the local PE BGP peering address and the
newly configured MDT group address (The NLRI format is 8-byte-RD:IPv4-address followed by the
MDT group address). This update is sent to all the BGP peers including PE2. The BGP process on PE2
receives this MDT update and notifies PIM. If the group is a PIM–SSM group, PIM on PE2 begins
sending SSM joins to the BGP peering address on PE1 to establish an SSM tree in the core. This SSM
tree is used to carry PIM control traffic and multicast data traffic in the corresponding VRF.
In summary, PIM requires the following from BGP:
• A new BGP MDT SAFI, which carries the VRF RD and BGP local peering address and default MDT
group in its NLRI.
–
A notification mechanism from BGP to PIM about the availability of the MDT SAFI update.
–
A notification mechanism from PIM to BGP about the default MDT group address and source
address.
See Internet Engineering Task Force (IETF) draft-nalawade-idr-mdt-safi-03 for detailed information on
MDT SAFI.
Figure 10 Multiprotocol IBGP Updates for MVPN
How to Implement BGP on Cisco IOS XR Software
This section contains instructions for the following tasks:
• Enabling BGP Routing, page RC-44 (required)
• Configuring a Routing Domain Confederation for BGP, page RC-47 (optional)
• Resetting an eBGP Session Immediately Upon Link Failure, page RC-49 (optional)
• Logging Neighbor Changes, page RC-49 (optional)
• Adjusting BGP Timers, page RC-50 (optional)
• Changing the BGP Default Local Preference Value, page RC-51 (optional)
Service Provider
CE
PE1 PE2
VPN routesVPN
Send Receive
211301
P-joins
SSM
MP-iBGPMP-iBGP
P-joins
CE