Juniper JUNOSE 11.2.X BGP AND MPLS, Configuration Manual

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3.
Remote peers of Router A use the route-target membership advertised by Router A
to filter their VPN routes that are outbound to Router A. A peer advertises a VPN
route to Router A only when one of the following conditions is true
•
Router A advertised a default route-target membership.
•
Router A advertised membership in any of the route targets associated with the
VPN route.
4.
Router A then receives and processes the RT-MEM-NLRI attributes sent by its peers
to determine which VPN routes it advertises to the peers.
BGP speakers advertise and withdraw the RT-MEM-NLRI attribute in MP-BGP update
messages. BGP speakers ignore RT-MEM-NLRI attributes received from peers that have
not successfully negotiated this capability with the speaker.
If dynamic negotiation for the route-refresh capability is enabled, BGP negotiates the
route-refresh capability for the RT-MEM-AFI-SAFI address family when a peer is activated
in that family. As a consequence, you can use the
clear ip bgp soft command to refresh
the RT-MEM-NLRI routes in the BGP speaker’s Adj-RIBs-Out table.
The usefulness of BGP VPN route-target filtering depends on the sparseness of route
target membership among the VPN sites. In configurations where VPNs are members of
many route target communities—that is, route target membership is dense—the amount
of VPN NLRI exchange traffic is about the same regardless of whether route-target
filtering is configured.
Receiving and Sending RT-MEM-NLRI Routing Updates
RT-MEM-NLRI routing updates are processed in the following sequence:
1.
During the initial RT-MEM-NLRI route exchange that takes place when a session
with a peer is being brought up, BGP sends an End-of-RIB marker for
RT-MEM-AFI-SAFI that signals it has finished advertising route-target membership
information.
2.
Remote peers interpret the End-of-RIB marker for RT-MEM-AFI-SAFI to mean that
the BGP speaker has advertised all of its route target-memberships. If the BGP
speaker does not receive an End-of-RIB marker for RT-MEM-AFI-SAFI from a remote
BGP peer in the context of the route-target address family, by default the local BGP
speaker waits for 60 seconds before timing out.
3.
The BGP speaker then starts advertising its VPN routes. The routes are passed
through the outbound route-target membership filters for that peer.
4.
When a BGP speaker receives a RT-MEM-NLRI update message, it re-evaluates the
advertisement status of VPN routes that match the corresponding route target in
the peer's Adj-RIBS-Out table. This can result in an incremental update that
advertises or withdraws some routes for the VPN.
You can use the bgp wait-on-end-of-rib command to specify how long BGP waits for
the End-ofRIB marker from route-target peers.
415 Copyright © 2010, Juniper Networks, Inc.
Chapter 6: Configuring BGP-MPLS Applications