CEF Load-Bal vs. PPP MultiLink...

[abatson]

I'm buying a 2X T1 solution from my ISP since I need more bandwidth. They said they use CEF for load-balancing, so I started reading up on it. CEF is a per-destination balance at layer-3 of the OSI model, whereas PPP Multilink is a layer-2 balance that breaks apart the packets & reassembles at the destination. CEF load-balance runs the risk of unequal use of the circuits since it's per-destination; let say CNN.com is assigned to one ckt, and saturates that ckt. more than the other. Is anyone using CEF load-balancing with their ISP? --whats the util. across your links? I'd rather use Multilink even with the CPU hit, you get perfect 50/50 distribution that way..

Alex

alex.batson@honeywell-tsi.com

[donewald]

Alex,

Both methods have their strong points. CEF is capable of per-packet load sharing at this time though. So the per-destination issues you mention are not applicable. AS you also mention with MLPPP you'll take a pretty good (sometimes more than good depending on the platform) CPU hit. Check out this link on Cef per-packet load sharing configuration.

http://www.cisco.com/en/US/partner/products/sw/iosswrel/ps1831/products_configuration_guide_chapter09186a00800ca6ca.html

One important thing to keep in mind, regardless of the method you choose to use, is that your ISP will have to implement something in your downstream direction to give you loadsharing back to you. MLPPP would do this without to much action on your ISP's part. CEF per-packet, process switching, or other per packet load sharing mechanisms would need to be configured on their end.

Hope this helps you,

Don

[abatson]

First off, my CCO login doesn't look like it has enough privs to get to the link you posted... CEF balancing only implements per-packet balancing right now? Not per-destination? (IOS Maturity issue, or platform issue?) Can I put two T1 WICS in a 2611XM router, and do CEF balancing that way? Also, it seems to be true that you have to turn off "ip route-cache" when doing MLPPP, it has to be process-switched all the time?

-Alex

[donewald]

Alex,

Send me your email and I'll send you the doc in pdf form. CEF by default, as you mentioned does per destination only. No, you don't have to disable ip route-cache when doing MLPPP. Yes, the mulilink functions on a 2611XM are done by the central processor.

Hope this helps you,

Don