Multiple BGP AS on Cisco Router

When you need to have BGP sessions from an AS number different that the one configured with router bgp as-number. As Cisco doesn't support multiple instances of BGP like the way juniper supports it.


neighbor ip-address local-as as-number [no-prepend [replace-as [dual-as]]]

no-prepend: Does not prepend the local autonomous system number to any routes received from the eBGP neighbor.

replace-as: Prepends only the local autonomous-system number to the AS_PATH attribute. The autonomous system number from the local BGP routing process is not prepended.


http://www.cisco.com/en/US/tech/tk365/technologies_configuration_example09186a00800949cd.shtml

OSPF Load Blance

If multiple equal-cost, equal-path-type exist, OSPF load balances over a maximum of 16.

R1(config-router)#maximum-path [1-16]

Hot Potato Routing

Getting packets to external destinations out of the network at the closest exit point!

OSPF Reference Bandwidth

R1(config-router)#auto-cost reference-bandwidth [The reference bandwidth in terms of mbps]

default reference bandwidth is 100 mbps
Ensure configuration is consistent across all routers

NSSA and P-bit

If the NSSA's ABR receives a type 7 LSA with the P-bit set to one, it will translate the type 7 LSA into a type 5 LSA and flood it throughout the other areas. If the P-bit is set to zero, no translation will take place and the destination in the type 7 LSA will not be advertised outside of the NSSA.