North American Network Operators Group
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Re: Load balancing in routers

  • From: Mark Kent
  • Date: Mon Apr 08 14:05:42 2002 
>> > load balancing over multiple links uses a flow-hashed method. If you
>> > want per-packet load distribution you have to specifically enable it by
>> > saying "no ip route-cache" on each interface.
>> 
>> That is very deadly, please, don't anyone actually try that.

How so?  So it uses a little more cpu, but that may not be relevant in
a lot of applications (like down at the T1 level).

I've had a customer on the end of 8 T1, no ip route cache, on a 4700
(their end) and a 7206/300 (my end).  4700 runs a little hot, but survives.

Similarly, I currently have a couple of 4*T1, a 3*T1, and several 2*T1
on PA-MC-T3 ports on a 7206/300 with no issues whatsoever.  Max cpu
usage is 35%.  Everything works.

Now, contrast that with my first use of cef, this was back when the
only cef configuration was "ip cef" or something similar.  Very
difficult to screw things up when the config is a one-liner, and yet
when I turned this on the 7206 immediately crashed.  

-mark