Per-port CEF load sharing

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)

1 comment:

  1. I've sup720 on cisco 7600 series, which is not support per-packet cef load balancing. This two router connected using 2 E1 link. Do you have any idea, how to do load sharing in this environment?

    Mostly packet that passing the router, is came from single source to single destination and single port to. So per-port CEF load sharing is not suitable to.

    PPP Multilink has been tried, but showing weirdo thing, for complete detail you can see my post to cisco-nsp list: http://www.gossamer-threads.com/lists/cisco/nsp/66608
    Do you have any idea/solution?

    Thanks for your help

    ReplyDelete

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Ivan Pepelnjak, CCIE#1354, is the chief technology advisor for NIL Data Communications. He has been designing and implementing large-scale data communications networks as well as teaching and writing books about advanced technologies since 1990. See his full profile, contact him or follow @ioshints on Twitter.