Advertising Inactive Routes; Verifying An As Path - Juniper JUNOSE SOFTWARE FOR E SERIES 11.0.X - BGP AND MPLS CONFIGURATION GUIDE 2009-12-30 Configuration Manual

JUNOSe 11.0.x BGP and MPLS Configuration Guide

Advertising Inactive Routes

Under normal circumstances, routes that are not being used to forward
traffic inactive routes are not advertised to peers unless synchronization is enabled.
For example, suppose a BGP speaker receives a route to a particular prefix, determines
that it is the best route to the prefix, and stores the route in the IP routing table
(sometimes known as the forwarding information base, or FIB). This route might not
be used for forwarding to that prefix; for example, if you have configured a static
route to the same destination prefix. Because static routes have better administrative
distances than BGP received routes, IP will use the static route rather than the BGP
received route for forwarding traffic to that prefix. The BGP received route is inactive
and is not advertised to peers. You can use the bgp advertise-inactive command
to enable the advertisement of inactive received routes.
bgp advertise-inactive

Verifying an AS Path

You can use the bgp enforce-first-as command to cause BGP to compare the first
AS in the AS-path of a received route with the configured remote AS number of that
EBGP peer. If the check fails, BGP returns a notification message to the peer.
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Advertising Routes
This command takes effect immediately.
Use the no version to remove the aggregate route entry from the routing table.
See aggregate-address.
Use to enable the BGP speaker to advertise inactive routes best routes in the
IP forwarding table that are not being used to forward traffic. This feature is
disabled by default.
Issuing this command does not affect the BGP rules for best route selection, or
how BGP populates the IP forwarding table.
Example
host1(config-router)#bgp advertise-inactive
The new value is applied to all routes that are subsequently placed in the IP
routing table.
To apply the new value to routes that are already present in the IP routing table,
you must use the clear ip bgp * command (this command will bounce the BGP
sessions).
Use the no version to prevent the advertising of received BGP routes unless one
or both of the following are true:
The received route is in the BGP forwarding table and is being used to forward
traffic (the route is active).
Synchronization is enabled.
See bgp advertise-inactive.