Reference Guide

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 reflectors
Route reflectors (RRs) reorganize the IBGP core into a hierarchy and allow route advertisement rules. Route reflection divides
IBGP peers into two groups — client peers and nonclient peers.
● If a route is received from a nonclient peer, it reflects the route to all client peers
● If a route is received from a client peer, it reflects the route to all nonclient and client peers
An RR and its client peers form a route reflection cluster. BGP speakers announce only the best route for a given prefix. 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 reflection cluster,
where Router D is the route reflector. 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 reflect 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.
Multiprotocol BGP
Multiprotocol BGP (MBGP) is an extension to BGP that supports multiple address families—IPv4 and IPv6. MBGP carries
multiple sets of unicast and multicast routes depending on the address family.
You can enable the MBGP feature on a per router, per template, and/or a per peer basis. The default is the IPv4 unicast routes.
BGP session supports multiple address family interface (AFI) and sub address family interface (SAFI) combinations, BGP uses
OPEN message to convey this information to the peers. As a result, the IPv6 routing information is exchanged over the IPv4
peers and vice versa.
BGP routers that support IPv6 can set up BGP sessions using IPv6 peers. If the existing BGP-v4 session is capable of
exchanging ipv6 prefixes, the same is used to carry ipv4 as well as ipv6 prefixes. If the BGP-v4 neighbor goes down, it also
impacts the IPv6 route exchange. If BGP-v6 session exists, it continues to operate independently from BGP-v4.
Multiprotocol BGPv6 supports many of the same features and functionality as BGPv4. IPv6 enhancements to MBGP include
support for an IPv6 address family and Network Layer Reachability Information (NLRI) and next hop attributes that use the IPv6
addresses.
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