[nsp] OSPF load balancing

Ryan Roylance ryan@opsource.net
Thu, 14 Nov 2002 13:31:55 -0800


Thanks to another suggestion from the list I turned on ip cef, then on
each frame interface did ip load-sharing per-packet.  Everything worked
perfectly, CPU stayed down, the traffic is flowing along nicely.  Thanks
for the help.

ryan

-----Original Message-----
From: cisco-nsp-admin@puck.nether.net
[mailto:cisco-nsp-admin@puck.nether.net] On Behalf Of Stephen J. Wilcox
Sent: Thursday, November 14, 2002 13:18
To: Ryan Roylance
Cc: cisco-nsp@puck.nether.net
Subject: Re: [nsp] OSPF load balancing



On Thu, 14 Nov 2002, Ryan Roylance wrote:

> I have a design with 2 routers and two frame relay connections (1.5)
>      
> 
>          172.17.0.0/16       RA-----------a----------------RB
> 172.18.0.0/16
>                              RA-----------b----------------RB
> 
> I am running a single OSPF area utilizing the multiple path equal cost

> load balancing.  RA and RB are both Cisco 2621 routers.
> 
> The question is this, by default the equal cost load balancing is per 
> destination, so Im not getting a perfect balance,  I have a couple of 
> servers on each side that see heavy traffic and they keep on ending up

> on the same link which defeats the purpose of having two lines.  When 
> I switch to per packet load balancing the CPU on the routers goes way 
> up (from 8% over 5 minutes to 25% over 5 minutes) and the performance 
> drops ( I went from capping 1 at 1.5 to pushing 400 on each)  What 
> solutions have people used in the past to make things like this
happen?  Are the
> 2621's underpowered for what Im trying to do?   

thats the trouble with per packet .. what you actually do is turn off
the hardware switching and force it all onto the main CPU

the 2621s are fine, the trouble is the limitation of the routing
protocols

my suggestion to you would be to manually influence the traffic, you can
either do this with a few static routes for the high volume servers or
if you want to complicate your config you could advertise more specifics
for your servers and then use an offset list to influence the ospf route
to each specific

the simplest way is the static routes, in the event of a link failure
you'll still fall over to the alternate route but you will achieve the
traffic balancing you need..

Steve

> 
> thanks
> ryan
> 
> Ryan Roylance
> Technical Operations Manager
> OpSource
> 
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