From: Jensen, Brian D. (bdjensen@eschelon.com)
Date: Thu Jul 08 2004 - 10:44:03 GMT-3
Hi Larry,
Its because there are two unequal links pointing to a single low-bw link, in
this case 64k. It didn't seem right to me either, until I tried it. Sure
enough, both routes have the same metric. If I changed the bw on the 64k
link to equal the highest bw on the dual links, then the costs were unequal
as seen from R3.
64k 2mb
R1-------R2======R3
1mb
Thanks,
Brian
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
Larry Roberts
Sent: Wednesday, July 07, 2004 11:22 PM
To: ccielab@groupstudy.com
Subject: RE: Eigrp unequal load balancing problem
Maybe Im missing something here as Im no EIGRP expert but..
Why does R3 see the metric as the same for R1's Lo as the same over both
links ?
Shouldn't the metrics be different over each of the links ?
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Jensen, Brian D.
Sent: Wednesday, July 07, 2004 10:52 PM
To: 'Tim Fletcher'; ccie2be; Sergio Jimenez Arguedas; ccielab@groupstudy.com
Subject: RE: Eigrp unequal load balancing problem
Hi Tim,
My curiosity was piqued, so I set this up in the lab:
R1 Lo = 10.1.1.1
R3 Lo = 10.3.3.3
R2 Lo = 10.2.2.2
Topology is same as original diagram, R1----R2===R3. Between R2 and R3,
band on s0/0 is set to 2mb, and s0/1 is set to 1mb on both sides.
Here are the routes from R3's perspective:
D 10.2.2.0/24 [90/7519] via 10.100.1.1, 00:00:02, Serial0/0
[90/12539] via 10.200.1.1, 00:00:02, Serial0/1
D 10.1.1.0/24 [90/183771] via 10.200.1.1, 00:00:02, Serial0/1
[90/183771] via 10.100.1.1, 00:00:02, Serial0/0
Here are the routes from R2's perspective:
D 10.1.1.0/24 [90/181771] via 10.11.0.1, 00:00:02, Serial1/1
D 10.3.3.0/24 [90/7029] via 10.100.1.2, 00:00:02, Serial0/0
[90/12049] via 10.200.1.2, 00:00:02, Serial0/1
Its the strangest thing, I get load balancing between R2 and R3 in the ratio
of 2:1, but if the traffic goes from R1 to R3, then there is no load
balancing. I have tried using the variance, and even "traffic bal" under
eigrp on both sides, and the traffic still prefers the hi bw link, or s0/0.
These results are not what I expected to see. Now I too am asking, why is
this so?
Thanks,
Brian
> -----Original Message-----
> From: nobody@groupstudy.com [SMTP:nobody@groupstudy.com] On Behalf Of Tim
> Fletcher
> Sent: Wednesday, July 07, 2004 10:01 PM
> To: ccie2be; Sergio Jimenez Arguedas; ccielab@groupstudy.com
> Subject: Re: Eigrp unequal load balancing problem
>
> At 08:33 PM 7/6/2004, ccie2be wrote:
> >OK, guys. You're not getting it, so I'll give you a hint.
> >
> >The problem is that from R3's point of view, the 2 paths to R1 are
> >equal cost. This is because when Eigrp figures out the cost to a
> >destination,
> it
> >using the lowest bandwidth link anywhere along the path to the
> destination.
> >Since the path to R1's lo0 includes a single 64k link between R2 and
> >R1, from R3's point of view both paths to R1 are equal.
>
> That's not entirely true. EIGRP does use the lowest bandwidth link in
> the path, but it also uses the cumulative delay. So you will see a
> larger difference in the metrics to reach R2 than the metrics to reach R1.
>
> From R3's perspective, the two paths to R2 are going to have
> different bandwidth and delay values, but the two paths to R1 are only
> going to have a difference in the delay value. The difference will
> also be smaller because both paths will include the 64K link which
> will have a higher delay than either of the other links. So you should
> see a difference in the metrics to R1, but it will be much smaller.
>
>
> >That, unfortunately, is as much as I know. What I don't know is how
> >to overcome this problem such that R3 unequal load balances traffic
> >to R1
> just
> >llike it does with traffic to R2.
>
> How about changing the EIGRP k values to achieve what you're after.
> One possibility is to set them to only use delay, then set the delay
> very low on the 64K link from R2 to R1. This should give you pretty
> close to the same distribution.
>
>
>
> >----- Original Message -----
> >From: "Sergio Jimenez Arguedas" <sejimenez@its.co.cr>
> >To: <ccielab@groupstudy.com>
> >Sent: Thursday, July 22, 2004 8:14 PM
> >Subject: RV: Eigrp unequal load balancing problem
> >
> >
> >> Hi,
> >>
> >> I think traffic shara balanced is the option!!!
> >>
> >>
> >http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cg
> >cr/f
> ipr
> >> rp_r/1rfeigrp.htm#wp1024898
> >>
> >>
> >> Rgds,
> >>
> >>
> >> Sergio
> >>
> >>
> >> -----Mensaje original-----
> >> De: nobody@groupstudy.com [mailto:nobody@groupstudy.com]En nombre
> >> de ccie2be Enviado el: martes, 06 de julio de 2004 17:44
> >> Para: tycampbell@comcast.net; Group Study
> >> Asunto: Re: Eigrp unequal load balancing problem
> >>
> >>
> >> Nope, not the answer.
> >>
> >> Variance is already configured and unequal load balancing already
> >> works between R2 and R3.
> >>
> >> The problem is that while unequal load balancing works between R2 &
> >> R3, unequal load balancing *doesn't* work between
> >>
> >> R1 and R3.
> >>
> >> Why?
> >>
> >> And, what is the solution?
> >>
> >>
> >> ----- Original Message -----
> >> From: <tycampbell@comcast.net>
> >> To: "ccie2be" <ccie2be@nyc.rr.com>; "Group Study"
> <ccielab@groupstudy.com>
> >> Sent: Tuesday, July 06, 2004 7:06 PM
> >> Subject: Re: Eigrp unequal load balancing problem
> >>
> >>
> >> > I think variance may be the answer you are looking for
> >> >
> >> > variance of 2 should do it for this scenario
> >> >
> >> >
> >> > > Hi guys,
> >> > >
> >> > > Here's the scenario:
> >> > >
> >> > >
> >> > > 2 mbps
> >> > > R1 -----64k ----- R2 ========= R3
> >> > > 1 mbps
> >> > >
> >> > >
> >> > > All routers are running Eigrp. R2 and R3 have unequal load
> balancing
> >> > > configured.
> >> > >
> >> > > Traffic between R2's lo0 and R3's lo0 unequal load balances
> perfectly.
> >> > > However, traffic between R1's lo0 and R3's lo0 don't unequal
> >> > > load balance. In this case, traffic is balanced equally
> across
> >> the 2
> >> > > links between R2 and R3.
> >> > >
> >> > > What the best way to have twice as much traffic going over the
> >> > > 2
> mbps
> >> link
> >> > > from R3 to R2 as the 1 mbps link between those 2 routers?
> >> > >
> >> > >
> >> > > TIA, Tim
> >> > >
> >> > >
> >_____________________________________________________________________
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