Verifying An As Path - Juniper JUNOSE 11.2.X BGP AND MPLS Configuration Manual

JunosE 11.2.x BGP and MPLS Configuration Guide

Verifying an AS Path

bgp enforce-first-as
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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.
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.
Use to cause BGP to determine whether the first AS in the AS path of a route received
from an EBGP peer matches the remote AS number of that peer.
If the AS does not match, BGP sends a notification to the peer with the error code "
update message error" and error subcode " malformed as-path."
This feature is disabled by default.
Example
host1(config-router)#bgp enforce-first-as
Causes BGP to check the AS path of all routes received after you issue the command.
To apply the new behavior to routes that are already present in the BGP routing table,
you must use the clear ip bgp command to perform a soft clear or hard clear of the
current BGP session.
Use the no version to prevent the AS comparison from taking place.
See bgp enforce-first-as.
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