North American Network Operators Group

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RE: question about traffic eng/ Cisco CEF.

  • From: rdobbins
  • Date: Wed Aug 09 02:11:51 2000

They were right - I got three private messages thanking me for pointing out
this isn't a Cisco-help list, all accompanied with warnings that someone
would react like this.

There's a line between hands-on, case-specific config info of use and
interest to all providers vs. more basic how-do-I-do-this types of
discussions.  While Mr. Dale's explanation of CEF load-balancing was
accurate and succinct, the same information could've been found by the
original poster on CCO or USENET, or even via a quick telephone call to
Cisco pre-sales.

When I ask case-specific questions here, it's a) because I've done all the
research I can do on my own and come up short, and b) because I think the
question itself would be one that other operators would care about.  I had a
lot of questions about MPLS in a network-provider environment a few months
back when I converted my core to it (all my previous experience in it was in
private networks), but I didn't ask those here because I was able to get the
answers elsewhere and I didn't think the other folks on this list would be
interested in either the questions or the answers, anyway.

The remark wasn't meant in a snide tone, but to point out that there are
other resources available for such things, and that it's probably a good
idea to try those, first.

NANOG should -not- be the first place people ask questions of this type.

That answer your question?

-----Original Message-----
From: John Fraizer
To: [email protected]
Cc: [email protected]; [email protected]
Sent: 8/8/00 9:38 PM
Subject: RE: question about traffic eng/ Cisco CEF. 

On Tue, 8 Aug 2000 [email protected] wrote:

> This question is more appropriately asked in the USENET comp.dcom.*
> hierarchies.

Why do some people find it necessary to post snide remarks vs posting an
informative reply?  Don't you think it is possible that someone on NANOG
might perhaps know the answer of this question and be able to answer?
your snide remark intended impose a better S:N ratio in the list?  If
it would have been much better served had you posted it in private and
even better had you not posted it at all!

Sorry to all the other readers of the list but, I just can't stand this
"We're too good to answer your question" bull!

> -----Original Message-----
> From: Jaideep Chandrashekar [mailto:[email protected]]
> When I enable cef and set it to share load on a per destination mode,
> some reason, all the traffic to a destination takes a single route
> .. though the route table shows two equal cost paths.
> The only point I might be missing is that I am looking at very few
> connections (2-3) and that load sharing with cef might be engineered
> share load in a statistical sense (only kick in with large number of
> connections).
> Could anybody throw any light on this.

I may be wrong but, from what I can remember, what you describe as being
the problem is actually it working as designed.  Each time a new flow is
encountered, it is checked against the current tables.  If an interface
has not already been assigned to that destination prefix, it is done so
then.  If you have two total destinations, you're going to end up with
on each of your links.

Feel free to correct me if I'm wrong folks.  Just please, do it kindly.

John Fraizer
EnterZone, Inc.