[c-nsp] cef load-sharing and recursive routing

Xavier Nicollet xnicollet at gmail.com
Thu Jan 22 04:59:29 EST 2015


I have an issue with cef load-sharing used as a way to load-balance servers.

Cisco CEF tends to simplify some path, as in this exemple:

ip route web1 (directly attached)
ip route web2 (remote site)
ip route web3 (remote site)

We would like to have each server with a weight of 1, having one third of
the traffic.

However, CEF will count remote site as just one destination, leading to:

#show ip cef internal, epoch 8, RIB[S], refcount 6, per-destination sharing
  output chain:
    loadinfo 1A4EDAB4, per-session, 2 choices, flags 0083, 5 locks
    flags: Per-session, for-rx-IPv4, 2buckets
    2 hash buckets
      < 0 > IP adj out of Vlan9, addr
      < 1 > IP adj out of TenGigabitEthernet6/4, addr /SNIP/

Has you see all the destination that lead to path Te6/4 will be accounted
for just one path.
This is very annoying since we have the same routes configured on remote
site, which can lead to routing loops for some
@IP src / @IP dst couples.

Is there a way to force the router to put exactly the same weight for each
entry, without any path optimisation ?

We are using cisco 7600 with RSP720. To my knowledge, openflow and such are
not supported on this platform, right ?

Thank you for your help,

Xavier Nicollet

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