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New Member

load-based policy routing?

is it possible to kick in a policy route on 2600/3600s when a FR WAN link gets to a certain load or even a congested condition?

I'd like to send certain traffic types via internet VPN but only when then main (expensive) link is full/nearly full. i.e. don't want to go to the usage based internet if I haven't yet used what I'm paying a flat rate for.

5 REPLIES
Silver

Re: load-based policy routing?

EIGRP allows adjusting the routing K factors to permit route costs to reflect link loading, but it is disabled by default because it leads to unstable routing under many conditions. In your case, it might be possible to achieve your goal if you fudge the metrics so only the the frame relay cost changes with load.

Another solution is a monitoring program running on a local server that adjusts the router configuration as required. While this technique can avoid the stability problems, it can have significant implications for security.

Layer four load balancing boxes may also be able to do the job, but these may be overkill for you.

Good luck and have fun!

Vincent C Jones

www.networkingunlimited.com

Gold

Re: load-based policy routing?

Even if you set the k values in EIGRP, this won't work. The problem is that EIGRP doesn't pull the load and delay dynamically off the interface, they are only pulled when the bandwidth or delay changes, or the neighbor is restarted, or some other event.

Russ.W

Re: load-based policy routing?

Can't "backup load" command (used under interface conf mode) be an alternative way to achieve this?

New Member

Re: load-based policy routing?

sorry forgot to say OSPF is the routing protocol.

Surely there must be an IOS way for using a second parallel path for overflow only. I'm thinking it would work similar to additional ISDN B-channel kicking in when required but ideally on a per-layer4 basis e.g. start sending smtp via alternate path when performance or load gets to a predertermined value, and of course switch back to the main route when load eases.

I really want to avoid adding some kind of layer4+ dedicated unit(s) into the mix and all the admin & strange side effects/complexities they can introduce. Trying to keep it as clean as possible.

Awaiting those creative ideas (:

Gold

Re: load-based policy routing?

Hmm.... You want to do this at layer 4? Only with some sort of laye 4 unti can you do this today. I could check into adding this sort of capability, if you email me, through marketing and the other folks. At layer 3, this sounds like a reasonable request--when one link fills, simply drop to the second best path, given you know it's loop free, which is (generally) easy enough to know in EIGRP, OSPF, or IS-IS.

Russ.W

riw@cisco.com

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