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JunosE 11.2.x BGP and MPLS Configuration Guide
Figure 41: A Fully Meshed Autonomous System
142
Figure 42 on page 143 illustrates how you can create three sub-ASs within AS 29 to greatly
reduce the number of peering sessions. According to common practice, use a number
from the private range of AS numbers—from 64512 to 65535—to identify each sub-AS.
AS 29 is now a confederation of three sub-ASs: AS 64720, AS 64721, and AS 64722. Each
sub-AS consists of fully meshed IBGP peers. A slightly modified version of EBGP runs
between the sub-ASs: It acts like IBGP within an AS because the local-pref, MED, and
next-hop attributes are preserved across the sub-AS boundaries. To the external
neighbors, AS 29 appears the same as it ever was.
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