In designs with very low number of IP hosts, no per-destination load-sharing algorithm will work adequately. Consider, for example, an extranet design where a large number of IP hosts are NAT-ed to a single IP address which then accesses a single remote server.

In this design, all the traffic flows between a single pair of IP addresses, making per-destination load-sharing unusable.

Cisco has addressed this problem in IOS release 12.4(11)T with per-port CEF load sharing, which extends the CEF hashing function to include source and/or destination TCP or UDP port.

The global configuration command that enables per-port CEF load-sharing is ip cef load-sharing algorithm [ include-ports [source] [dest] ] seed. To test it, use the show ip cef exact-route command, which now supports source and destination port numbers. For example:

a1(config)#ip cef load-sharing algorithm include-ports source dest 22

a1#show ip cef exact-route 10.0.0.10 src-port 35 192.168.0.2 dest-port 80
10.0.0.10       -> 192.168.0.2    : Serial0/0/0.100 (next hop 172.16.1.2)
a1#show ip cef exact-route 10.0.0.10 src-port 36 192.168.0.2 dest-port 80
10.0.0.10       -> 192.168.0.2    : Serial0/0/0.200 (next hop 172.16.1.6)
a1#show ip cef exact-route 10.0.0.10 src-port 37 192.168.0.2 dest-port 80
10.0.0.10       -> 192.168.0.2    : Serial0/0/0.100 (next hop 172.16.1.2)