[nsp] OSPF load balancing

[Stephen J. Wilcox]

cool. the only thing to watch now is that individual flows will split over each
route, this might be okay however you might see degraded performance if packets
arrive out of order - a particular problem if you have realtime traffic. you'll
get this happening if the two circuits have differing latency or when they start
getting full and queuing data such that different amount of jitter is
introduced.

Steve

On Thu, 14 Nov 2002, Ryan Roylance wrote:

> 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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