Juniper BGP, Configuration Manual

Page: 180 / 748

For example, in an AS with 9 BGP peers, the peers can conduct 36 sessions:
BGP provides the following two alternative configuration strategies to reduce the
number of fully meshed peers:
■
Configure confederations.
■
Configure route reflectors.
Both of these strategies are complex and can create their own problems. Neither
strategy is typically used unless the mesh of IBGP peers approaches 100 sessions
per peer.
Configuring a Confederation
IBGP requires that BGP speakers within an AS be fully meshed. You can reduce the
IBGP mesh inside an AS by subdividing the AS into a confederation of sub-ASs. Each
sub-AS must be fully meshed internally, but the sub-ASs do not have to be fully
meshed with each other. Confederations are most useful when the number of IBGP
speakers within an AS increases to the point that each router has about 100 peering
sessions.
Figure 41 on page 145 shows a simpler topology. AS 29 consists of 10 fully meshed
IBGP peers (for clarity, only the BGP sessions are shown). Border router Salem has
an EBGP session with a neighbor in AS 325. Border router Boston has an EBGP session
with a neighbor in AS 413.
144 ■
Managing a Large-Scale AS
JUNOSe 11.1.x BGP and MPLS Configuration Guide