Avaya 8800 Planning And Engineering, Network Design page 128

Layer 3 network design
Figure 50: 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).
Figure 51: Multiple regions separated by IBGP
In this figure, consider the following:
• The AS is divided into three regions that each run different and independent IGPs.
June 2016 Planning and Engineering — Network Design
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