Avaya 8800 Planning And Engineering, Network Design page 129

• Regions are logically interconnected via a full-mesh IBGP, which also provides Internet
connectivity.
• Internal nonBGP routers in each region default to the BGP border router, which contains all
routes.
• If the destination belongs to any other region, the traffic is directed to that region; otherwise, the
traffic is sent to the Internet connections according to BGP policies.
To set multiple policies between regions, represent each region as a separate AS. Then, implement
EBGP between ASs, and implement IBGP within each AS. In such instances, each AS injects its
IGP routes into BGP where they are propagated to all other regions and the Internet.
The following figure shows the use of EBGP to join several ASs.
Figure 52: Multiple regions separated by EBGP
You can obtain AS numbers from the Inter-Network Information Center (NIC) or use private AS
numbers. If you use private AS numbers, be sure to design your Internet connectivity very carefully.
For example, you can introduce a central, well-known AS to provide interconnections between all
private ASs and/or the Internet. Before propagating the BGP updates, this central AS strips the
private AS numbers to prevent them from leaking to providers.
The following figure illustrates a design scenario in which you use multiple OSPF regions to peer
with the Internet.
June 2016 Planning and Engineering — Network Design
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Border Gateway Protocol
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