Using A Single As Number For All Ce Sites - Juniper BGP - CONFIGURATION GUIDE V 11.1.X Configuration Manual

Using a Single AS Number for All CE Sites

If you want to use the same AS number for all of your CE sites, you can substitute a
PE router's autonomous system number for that of a neighbor by specifying the
neighbor's IP address in the neighbor as-override command. If you fail to do this,
the CE router recognizes its AS in the AS path of received routes and determines it
has discovered a routing loop; the routes are rejected.
In the following example, the router's AS number of 777 overrides the neighboring
Example
router's AS number of 100.
neighbor as-override
host1:vr1(config)#router bgp 777
host1:vr1(config-router)#neighbor 172.16.20.10 remote-as 100
host1:vr1(config-router)#neighbor 172.16.20.10 update-source loopback0
host1:vr1(config-router)#address-family ipv4 vrf vpn1
host1:vr1(config-router-af)#neighbor 172.25.14.12 remote-as 100
host1:vr1(config-router-af)#neighbor 172.25.14.12 as-override
Use to enable the use of the same AS number for all CE sites by substituting the
current router's AS number in routing tables for that of the neighboring router.
If you specify a BGP peer group by using the peer-group-name argument, all the
members of the peer group inherit the characteristic configured with this
command. You cannot override the characteristic for a specific member of the
peer group.
New policy values are applied to all routes that are sent (outbound policy) or
received (inbound policy) after you issue the command.
To apply the new policy 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.
Behavior is different for outbound policies configured for peer groups for which
you have enabled Adj-RIBs-Out. If you change the outbound policy for such a
peer group and want to fill the Adj-RIBs-Out table for that peer group with the
results of the new policy, you must use the clear ip bgp peer-group command
to perform a hard clear or outbound soft clear of the peer group. You cannot
merely perform a hard clear or outbound soft clear for individual peer group
members because that causes BGP to resend only the contents of the Adj-RIBs-Out
table.
Example 1
host1:vr1(config-router)#neighbor 192.168.255.255 as-override
Example 2
host1(config-router)#neighbor 192.168.1.158 as-override
Chapter 5: Configuring BGP-MPLS Applications
Configuring BGP VPN Services
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