Juniper BGP, Руководство по настройке

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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.
When the route-refresh capability has been negotiated for the route-target address
family. BGP handles route-refresh messages for the RT-MEM-AFI-SAFI by resending
all RT-MEM-NLRI routes to the remote peer
You can use the neighbor maximum-prefix command to specify the maximum
number of prefixes that the speaker can receive from a BGP peer.
Route-target filtering generally follows the standard BGP rules for route advertisement
to determine when to advertise RT-MEM-NLRI prefixes that have been received from
BGP peers. Table 61 on page 412 lists the destinations that the prefixes are advertised
to based on their source. In this table, client-to-client reflection is enabled and the
source and destination peers are not the same.
Table 61: Route-Target Filtering Advertisement Rules for Routes Received from
Peers
Advertise to EBGP
Confederation
Peer? Advertise
to EBGP
Peer?
Advertise to
IBGP Route
Reflector
Nonclient? Advertise to
IBGP Route
Reflector
Client?
Routes Received From
Yes Yes Yes Yes IBGP route reflector client
412 ■
Constraining Route Distribution with Route-Target Filtering
JUNOSe 11.1.x BGP and MPLS Configuration Guide