Which two statements about Cisco Express Forwarding load balancing are true? (Choose two)

Which two statements about Cisco Express Forwarding load balancing are true? (Choose two)
A . Each hash maps directly to a single entry in the RIB
B . It combines the source IP address subnet mask to create a hash for each destination
C . Cisco Express Forwarding can load-balance over a maximum of two destinations
D . It combines the source and destination IP addresses to create a hash for each destination
E . Each hash maps directly to a single entry in the adjacency table

View Answer

Answer: D E

Explanation:

Cisco IOS software basically supports two modes of CEF load balancing: On per-destination or perpacketbasis.

For per destination load balancing a hash is computed out of the source and destination

IP address (-> Answer ‘It combines the source and destination IP addresses to create a hash for each destination’ is correct). This hash points to exactly one of the adjacency entries in the adjacency table (-> Answer ‘Each hash maps directly to a single entry in the adjacency table’ is correct), providing that the same path is used for all packets with this source/destination address pair. If per packet load balancing is used the packets are distributed round robin over the available paths. In either case the information in the FIB and adjacency tables provide all the necessary forwarding information, just like for non-load balancing operation.

The number of paths used is limited by the number of entries the routing protocol puts in the routing table, the default in IOS is 4 entries for most IP routing protocols with the exception of BGP, where it is one entry. The maximum number that can be configured is 6 different paths -> Answer ‘Cisco Express Forwarding can load-balance over a maximum of two destinations’ is not correct.