RE: PBR

From: David Sinn (dsinn@microsoft.com)
Date: Tue Jul 31 2001 - 21:34:32 EDT


The simple answer is "no", but you have other options.

Cisco's load balancing is not intelligent, and is not balancing. It is
a fixed hash over the given number of links that cause a given flow to
always use the same link out of a given router. There is no feedback
mechanism. Thus you can have very clumpy traffic (especially on slower
speed links).

If you aren't on a GSR, then you could turn on CEF per-packet load
balancing but this means you need to run CEF, and very few people do
this, so you mileage will vary (i.e.. If you don't want to run CEF you
can turn off all route-caching and the router will per-packet load
balance by default. This method is not very elegant, but depending on
load MIGHT be acceptable. Either way you are telling the router to load
balance the traffic on a per-packet basis across the parallel links.
This can result in out-of-order delivery of traffic, so consider if that
is important to you. Also it is not a guarantee that the traffic will
still be well balanced, but is a better shot then having the flow based
load balancing you have now and resulting in the clumpy traffic you are
seeing.

You can also consider more L2 load balancing such as MLPPP or ATM-IMA.

ATM-IMA can work if you are talking about T-1's, and last I checked the
PA/NM's supported 8 T1's. It does mean you have to run ATM, which is
mostly considered a four letter word, so think about it deeply before
you jump. You also loose a fair amount total throughput due to
overhead, so you have even more to consider if you are on slow links.

MLPPP could also be an option, and is possibly your best if you control
both ends, and can take the CPU hit that it creates.

All in all it depends on what box you are on, and how much pain you can
endure.

David

-----Original Message-----
From: Fillet Platoon [mailto:fplatoon@yahoo.com]
Sent: Monday, July 30, 2001 8:39 PM
To: cisco-nsp@puck.nether.net
Subject: PBR

hello guys,

    my goal is to load balanced my point-to-point
links that have 8 parallel serial connection, so i
used EIGRP as my routing protocol and i used MHSRP
along with PBR on some of my selective source address.
Is there a routing protocol that intelligent enough to
detect that my Serial 0 connection is congested and i
will automatically redirect it to serial 1 or Serial 2
that is not congested? If not is there a way to solve
it? Is there a features in Cisco IOS that
automatically detect that the link is congested and
automatically redirect it to another link that is not
congested?

rgds,
fillet

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