Avaya 8800 Planning And Engineering page 135

Figure 51: BGP and edge aggregation
BGP and ISP segmentation
You can use the switch as a peering point between different regions or ASs that belong to the
same ISP. In such cases, you can define a region as an OSPF area, an AS, or a part of an AS.
You can divide the AS into multiple regions that each run different Interior Gateway Protocols
(IGP). Interconnect regions logically via a full IBGP mesh. Each region then injects its IGP
routes into IBGP and also injects a default route inside the region. Thus, for destinations that
do not belong to the region, each region defaults to the BGP border router.
Use the community parameter to differentiate between regions. You can use this parameter in
conjunction with a route reflector hierarchy to create large VPNs. To provide Internet
connectivity, this scenario requires you to make your Internet connections part of the central
IBGP mesh (see the following figure).
Planning and Engineering — Network Design
Border Gateway Protocol
November 2010 135