Route Selection When Route-Target Filtering Is Enabled - Juniper BGP - CONFIGURATION GUIDE V 11.1.X Configuration Manual

JUNOSe 11.1.x BGP and MPLS Configuration Guide

Route Selection When Route-Target Filtering Is Enabled

When route-target filtering is enabled for a peer, BGP applies outbound filters to
initially prevent the speaker from advertising any VPN routes to the peer.
If the BGP speaker subsequently receives a Default-MEM-NLRI route from a peer,
BGP applies outbound filters for the peer to prevent route-target filtering from
suppressing any VPN routes sent to the peer.
BGP follows the standard route selection process to find the route-target filtering best
path for RT-MEM-NLRI routes received from other autonomous systems. The selection
is based on the AS path and other MP-NLRI path-attributes attached to the route.
The route-target membership information, which includes the route target and the
originator AS number, enables BGP speakers to use the standard path selection rules
to remove duplicate, less-preferred paths from the total set of paths to route-target
membership peers.
For RT-MEM-NLRI routes that originated within the local AS and are received from
an IBGP peer, BGP considers the route-target filtering best path to be the set of all
available IBGP paths for the RT-MEM-NLRI prefix. BGP then sets outbound route
filters so that VPN routes that match the route target are sent to all IBGP peers that
advertised the RT-MEM-NLRI route. This behavior does not affect how the BGP speaker
in turn advertises the RT-MEM-NLRI routes.
When BGP selects a RT-MEM-NLRI route from a peer as the best path for the
RT-MEM-NLRI prefix, BGP modifies the outbound filters to enable the speaker to
advertise to that peer all VPN routes that correspond to that route target. These filters
affect the subsequent calculation of the peer's Adj-RIBs-Out entries.
EBGP confederation peers are treated as IBGP peers when the BGP speaker is selecting
the route-target filtering best path. When the BGP speaker advertises routes, then
the EBGP confederation peers are treated normally, as EBGP peers.
416
Constraining Route Distribution with Route-Target Filtering
command. You cannot override the characteristic for a specific member of the
peer group.
Outbound policy configured for the neighbor (using the neighbor route-map
out command) is not applied to default routes that are advertised because of the
neighbor default-originate command.
This command takes effect immediately.
Example
host1(config)#router bgp 100
host1(config-router)#router address-family route-target
host1(config-router-af)#neighbor default-originate
Use the no version to prevent the default route from being advertised by BGP.
Use the default version to remove the explicit configuration from the peer or
peer group and reestablish inheritance of the feature configuration.
See neighbor default-originate.