Refer to the exhibit. BGP-4 routing to the Internet, in normal behavior, may create asymmetrical
routing for different prefixes. The BGP routing table indicates that traffic should follow the paths
indicated in the exhibit, but packets are not going further than the border router in AS 4. What
could be the cause of this problem?
A.
TCP Intercept is configured in AS 4.
B.
Unicast Reverse Path Forwarding is configured in loose mode in this router.
C.
Packets may be leaving AS 1 without the BGP routing flag set to 1.
D.
Unicast Reverse Path Forwarding is configured in strict mode in this router.
E.
There is a missing Unicast Reverse Path Forwarding configuration.
Explanation:
When administrators use Unicast RPF in strict mode, the packet must be received on the interface
that the router would use to forward the return packet. Unicast RPF configured in strict mode may
drop legitimate traffic that is received on an interface that was not the router’s choice for sending
return traffic.
Dropping this legitimate traffic could occur when asymmetric routing paths are present in the
network.http://www.cisco.com/web/about/security/intelligence/unicast-rpf.html