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15. EBGP Scalability Issues
15.1 Using Policies to Limit EBGP Routes
Route policies can be used to limit the number of EBGP routes to reduce the number of BGP forwarding
routes. Within a customer AS, a default route can be injected into the local IGP by the EBGP peering
router or routers to reduce the route table size for all non-BGP routers. Please note that the ERS8000
supports up to 250,000 BGP forwarding routes in its routing information base (RIB) and 500,000 in its
forwarding information base (FIB). The VSP9000 as of release 4.0 and using generation 2 modules can
support up to 1 million route operations.
15.1.1 Configuration Example: Using AS List to Limit Route
Table Size
Figure 18: BGP AS Path Filtering Example
8008 is connected to three separate AS's all supplying full internet routes. For this example, we wish to
reduce the number of routes accepted from each EBGP connection on switch 8008. One method to do
this is to apply a policy to each EBGP connection with an IP prefix list to suppress routes. For example, if
we add a route policy with an IP prefix list mask length of 18 bits to each EBGP connection, this will
reduce the number of routes on each connection to approximately 22,000 routes for a total of 66,000
routes.
For this example, three route policies will be added. We will add a route policy to inject a default route into
AS 22000 assuming the IGP is OSPF. Another route policy will be added and applied to each EBGP peer
to reduce the number of routes learned by applying an IP prefix with a mask length of 18. In addition, we
will add another policy to block 8008 from sending out any routing information from any of the three
EBGP peers; we do not want 8008 from becoming a transit router for the other ASs.
Please note that the VLAN and/or brouter port and OSPF configuration is not provided for this
configuration example.
Avaya Inc. – External Distribution
98
January 2016
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