Enabling Route Storage In Adj-Ribs-Out Tables - Juniper BGP - CONFIGURATION GUIDE V 11.1.X Configuration Manual

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host1#show ip bgp summary
Local router ID 10.1.0.1, local AS 1
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Enabling Route Storage in Adj-RIBs-Out Tables

By default, a BGP speaker does not store a copy of each route it sends to a BGP peer
in the Adj-RIBs-Out table for that peer. However, you can force BGP to store a copy
of routes in the Adj-RIBs-Out table for a particular peer or peer group by enabling
that Adj-RIBs-Out table (" enabling rib-out" ) with the no neighbor rib-out disable
command. Alternatively, you can use the no rib-out disable command to affect all
BGP peers. The details of route storage vary between peers and peer groups.
For peers, BGP stores a single bit with each route in the table to indicate whether it
has previously advertised the route to the peer, enabling the avoidance of spurious
withdrawals. The full set of attributes for each route is not stored in the peer
Adj-RIBs-Out table.
After enabling rib-out for a peer, you can issue the show ip bgp neighbors
advertised-routes command to display the routes that have been advertised to the
peer. The attributes displayed for the routes are those from the local routing table,
not those that were advertised. In other words, BGP stores the attributes prior to the
application of any outbound policy.
For peer groups, BGP stores the full set of attributes associated with the route after
the application of any outbound policy; that is, it stores the attributes as they will be
advertised. BGP does not store a bit to track whether a route was advertised to the
peer group. Storing the full attribute set for each peer group route is memory intensive
but acceptable for peer groups, because the number of peer groups is relatively small.
An advantage of enabling rib-out for peer groups is that convergence is accelerated
because the attributes for each route are already determined for all routes to be
advertised to the peer group. BGP has to apply outbound policy only once for each
route rather than once for each peer for each route.
After enabling rib-out for a peer group, you can issue the show ip bgp
advertised-routes command to display the routes that will be advertised to the peer
group and the attributes (after the application of any outbound policy) that will be
advertised with the routes.
When you have enabled rib-out for individual peers or a peer group, before sending
an advertisement or withdrawal the router compares the route it is about to send
with the last route sent for the same prefix (and stored in the Adj-RIBs-Out table for
the peer or peer group) and sends the update message only if the new information
is different from the old.
The comparison prevents the sending of unnecessary withdrawals for both peers
and peer groups, because the BGP speaker will not send a withdrawal if the table
indicates it has not previously advertised that route to the peer. However, because
the route attributes are no longer stored with the routes in peer Adj-RIBs-Out tables,
Administrative state is Start
Operational state is Down due to transition from Overload state
Shutdown in overload state is enabled
Default local preference is 100
Chapter 1: Configuring BGP Routing
Configuring BGP Peer Groups
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