From: ccie2be (ccie2be@nyc.rr.com)
Date: Wed Jun 16 2004 - 17:48:22 GMT-3
Ty,
Your question prompted me to double check my understanding of this topic.
Fortunately, I happen to have an old copy of Routing TCP/IP by Jeff Doyle.
His explanation and examples are excellent.
To summerize:
-The traffic-share min command causes the Cisco IOS software to divide
traffic only among the routes with the best metric. Other routes will remain
in the routing table, but will receive no traffic. Configuring this command
with the across-interfaces keyword allows you to configure multi-interface
load splitting on different interfaces with equal cost paths.
-Use the variance # command to configure unequal load-balancing. Any routes
where the metric < metric of lowest cost route x variance will be added to
the route table and will be used to the extent of it's inversely proportion
metric e.g. if the metric is 3 times that of the lowest cost route, it will
get 1/3 of the traffic. That's because, by default, the unseen command
traffic-share balanced is configured.
-If multiple routes s/b in the route table but only the best route should be
used, use the both variance # command and traffic-share min commands.
Without the variance command, only the best route will be in the route
table.
HTH
----- Original Message -----
From: <tycampbell@comcast.net>
To: "John Matijevic" <matijevi@bellsouth.net>
Cc: "Marvin Greenlee" <marvingreenlee@yahoo.com>; <ccielab@groupstudy.com>
Sent: Wednesday, June 16, 2004 4:28 PM
Subject: Re: eigrp variance
> Thanks John...sometimes the frustration of the day gets to me..as I sure
it does to all of us, when you have to follow behind and clean some messes
up...if you know what I mean.....arrggh...hahahah...but I still love my
job...just a bad day...glad it doesn't happen very often...if you know what
I mean...and I apologize...
>
> I did find the article helpful, but I am still having an issue fully
understanding the concept...it looks very simple...and I am most likely not
thinking on those terms
>
> ok...
>
> here's what I am having a hard time grasping..
> going on the example of the article....
>
> router with metric of 20
> router with metric of 30
>
> variance is set to 40.... 2*20 = 40 ok...I'm good so far...
>
> then the variance is 2....shouldn't it be 3, as 2*20 = 60, which is also
divisible by 30 ?
>
> now that the metric of the 20 is set to 40...wouldn't the one with the
metric of 30 be preferred...I guess I am looking at this from a perspective
of the metrics need to match for each route in order to be balance
properly...I though asking for a formula may help me understand this better,
but I still don't see the metrics being the same for each route...that is
what is confusing me...any insight into this would be greatly appreciated...
>
>
> > Hello Ty,
> > I apologize if I offended you. I wasnt saying that you didnt do any
> > research, I was just making a general observation.
> > Again, my sincere apologies, this is a great forum, with very good
> > engineers, we can all try and make this a better place. I hope you find
the
> > article I provided you as well to be helpful.
> > Sincerely,
> > Matijevic
> > ----- Original Message -----
> > From: <tycampbell@comcast.net>
> > To: "John Matijevic" <matijevi@bellsouth.net>
> > Cc: "Marvin Greenlee" <marvingreenlee@yahoo.com>;
<ccielab@groupstudy.com>
> > Sent: Wednesday, June 16, 2004 8:37 AM
> > Subject: Re: eigrp variance
> >
> >
> > > John,
> > >
> > > I wasn't trying to be lazy or anything, I do searches for everything
> > before posting a question, when I don't fully understand something from
the
> > documentation. I did research, before I posted the question. We all
learn
> > from asking questions. If the purpose of the forum is to not ask
questions
> > and learn about something we don't understand, then I will refrain from
> > doing so. However, as I stated before, I am fully aware of doing a
search,
> > which I have already done. That is why the question was posted. My very
> > first search was actually done on the DOC CD under eigrp. I did not
fiind
> > anything on the DOC CD that under eigrp that even stated anything about
> > variance. It wasn't my last search however. By your response, you are
> > stating that I did not do that, without even asking me first. Once
again,
> > the only reason I posted the question was to try to get more
understanding
> > about it. I didn't post the question looking for an easy way out. aA
few
> > people responded...it gave me bet!
> > > ter insight to this, and I understand it better now, and I appreciate
> > their response.
> > >
> > > Ty
> > >
> > >
> > > > Ty,
> > > > The answer to your question can be done by doing a simple search.
Let me
> > > > explain how to do this. First you go to www.cisco.com/support, or an
> > archive
> > > > or google, etc., Next, in the search box type variance, next you
will
> > see
> > > > seeveral articles or messages pop up, if there are too many you can
try
> > and
> > > > use a more descriptive search or try to be more specific in your
search.
> > If
> > > > there are not as many articles or messages, then you maybe too
specific
> > and
> > > > have to be general in your search. Sometimes you have to use more
than
> > one
> > > > resource, sometimes you have to experiment with different words,
etc.
> > For
> > > > the question you had I simply went to www.cisco.com/support, then I
> > typed in
> > > > variance in the search box. Then I read the following article which
> > > > describes the function of the command. Finally, I am not trying to
> > insult
> > > > intelegence here but merely pointing out a method that has worked
for
> > me. I
> > > > have observed many times that people do not search the archives or
do
> > proper
> > > > research before posting. Sure its easier to post the question then
to
> > do
> > > > the research yourself. But you will become a better engineer by
finding
> > the
> > > > answer yourself. At least try to make an effort. Maybe I have so
much
> > time
> > > > now that I am not working that I can support this forum, and try and
> > make
> > > > this a better place for everyone. I hope nobody takes offense to
this
> > post,
> > > > but uses this as constructive feedback.
> > > > Here is the article:
> > > >
> >
http://www.cisco.com/en/US/tech/tk365/tk207/technologies_tech_note09186a0080
> > > > 09437d.shtml
> > > >
> > > > Sincerely,
> > > > Matijevic
> > > > ----- Original Message -----
> > > > From: "Ty" <tycampbell@comcast.net>
> > > > To: "Marvin Greenlee" <marvingreenlee@yahoo.com>
> > > > Cc: <ccielab@groupstudy.com>
> > > > Sent: Wednesday, June 16, 2004 3:26 AM
> > > > Subject: Re: eigrp variance
> > > >
> > > >
> > > > > Thanks Marvin!
> > > > > ----- Original Message -----
> > > > > From: "Marvin Greenlee" <marvingreenlee@yahoo.com>
> > > > > To: "Ty" <tycampbell@comcast.net>
> > > > > Cc: <ccielab@groupstudy.com>
> > > > > Sent: Tuesday, June 15, 2004 9:58 PM
> > > > > Subject: Re: eigrp variance
> > > > >
> > > > >
> > > > > > Divide the larger metric path by the smaller metric
> > > > > > path.
> > > > > >
> > > > > >
> > > > > >
> > > > > > The variance command is related to the eigrp metric
> > > > > > calculation.
> > > > > >
> > > > > > "...If k5 equals 0, the composite IGRP or EIGRP metric
> > > > > > is computed according to the following formula:
> > > > > >
> > > > > > metric = [k1 * bandwidth + (k2 * bandwidth)/(256 -
> > > > > > load) + k3 * delay]
> > > > > >
> > > > > > If k5 does not equal zero, an additional operation is
> > > > > > performed:
> > > > > >
> > > > > > metric = metric * [k5/(reliability + k4)]
> > > > > >
> > > > > > Bandwidth is inverse minimum bandwidth of the path in
> > > > > > BPS scaled by a factor of 2.56*1012. The range is from
> > > > > > a 1200-bps line to 10 terabits per second. ..."
> > > > > >
> > > > > > The variance command is a multiplier for what you
> > > > > > consider a valid path for load balancing. If your
> > > > > > metric were 3, you would be saying that the router can
> > > > > > load balance any paths with a metric that is up to 3
> > > > > > times the metric of the path with the lowest metric.
> > > > > >
> > > > > >
> > > > > > Marvin Greenlee
> > > > > > Network Learning, Inc.
> > > > > > marvin@ccbootcamp.com
> > > > > >
> > > > > >
> > > > > >
> > > > > > --- Ty <tycampbell@comcast.net> wrote:
> > > > > > > what is the formula for configuring variance for
> > > > > > > eigrp ?
> > > > > > >
> > > > > > > Thanks!
> > > > > > >
> > > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > > __________________________________
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This archive was generated by hypermail 2.1.4 : Sat Jul 03 2004 - 19:40:42 GMT-3