Reference Guide

Established Keepalive messages exchange, and after a successful receipt, the router is in the Established state. Keepalive
messages continue to send at regular periods. The keepalive timer establishes the state to verify connections.
After the connection is established, the router sends and receives keepalive, update, and notication messages to and from its peer.
Peer templates
Peer templates allow BGP neighbors to inherit the same outbound policies. Instead of manually conguring each neighbor with the same
policy, you can create a peer group with a shared policy that applies to individual peers. A peer template provides ecient update
calculation with simplied conguration.
Peer templates also aid in convergence speed. When a BGP process sends the same information to many peers, a long output queue may
be set up to distribute the information. For peers that are members of a peer template, the information is sent to one place then passed on
to the peers within the template.
Route reectors
Route reectors (RRs) reorganize the IBGP core into a hierarchy and allow route advertisement rules. Route reection divides IBGP peers
into two groups — client peers and nonclient peers.
• If a route is received from a nonclient peer, it reects the route to all client peers
• If a route is received from a client peer, it reects the route to all nonclient and client peers
An RR and its client peers form a route reection cluster. BGP speakers announce only the best route for a given prex. RR rules apply
after the router makes its best path decision.
NOTE
: Do not use RRs in forwarding paths — hierarchal RRs that maintain forwarding plane RRs could create route loops.
Routers B, C, D, E, and G are members of the same AS—AS100. These routers are also in the same route reection cluster, where Router D
is the route reector. Routers E and G are client peers of Router D, and Routers B and C and nonclient peers of Router D.
1 Router B receives an advertisement from Router A through EBGP. Because the route is learned through EBGP, Router B advertises it
to all its IBGP peers — Routers C and D.
2 Router C receives the advertisement but does not advertise it to any peer because its only other peer is Router D (an IBGP peer) and
Router D has already learned it through IBGP from Router B.
3 Router D does not advertise the route to Router C because Router C is a nonclient peer. The route advertisement came from Router
B which is also a nonclient peer.
4 Router D does reect the advertisement to Routers E and G because they are client peers of Router D.
5 Routers E and G advertise this IBGP learned route to their EBGP peers — Routers F and H.
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