Need help with EIGRP unequal cost routing

I've got a situation where I have a connection to a remote office over

2 T1s. The router on this end is a 4700 and the remote side is using a 2621. About 10 channels of one of the T1s is being used for voice. Currently, the configuration looks like:

interface Serial1 bandwidth 192 ip unnumbered Ethernet0

interface Serial2 bandwidth 112 ip unnumbered Ethernet0

ip route x.y.z.0 Serial1 ip route x.y.z.0 Serial2

I was hoping that the bandwidth statements would help the router distribute the packets between the two links accordingly, but it looks like I was mistaken.

I'm trying to look into EIGRP unequal cost routing to fix this situation I've been reading about it, but I'm not sure how to apply it to this situation. Could someone come up with a sample configuration?

My goal here is to get maximum usage out of the available bandwidth. If you look at the stats on that router, the maximum traffic going through to the other location is only a little less than a full T1's worth.

Thank you!

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Hi please post sh ip eigrp top x.y.z.0 sh ip route x.y.z.0

do you have "variance x" in your eigrp config?

Roman Nakhmanson

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Roman Nakhmanson

The EIGRP routing process variance command is the magic knob that you are looking for along with the traffic-share command.

Figure out the EIGRP metric for each unequal cost route between the two locations. By default, EIGRP uses bandwidth and delay to compute routing metrics - thus it is a composite metric.

configure the actually bandwidth available for data traffic on each interface. This is important for a couple of reasons - one it is used in the metric calculation and it is also the value that would be retrieved by SNMP to do bandwidth utilization calculations.

If you want to prefer one path over another, you should always change the interface delay value.

Increase the variance until the desired result is accomplished that is both paths being used

router eigrp variance 1 ! use equal cost routes only (defualt behaviour) traffic-share balanced exit

router eigrp variance 2 ! use all routes which fall within 2 x minimum path metric traffic-share balanced exit

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I'm sorry if I was being unclear. The config I gave in my original post was what we are using now. We aren't yet using EIGRP, so I really can't post anything about a config that doesn't exist yet. I think I have some understanding of how the variance command works, but I still don't know how to apply it to my situation. Is the config shown in Merv's post all that I need on both sides? Does EIGRP find it's neighbors automatically? Maybe it's simpler than I expected. I'm continuing to read...

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Ahhhhh you were try to load balance with static routes - that will not work unless they are equal-cost

Configuring EIGRP is quite straight-forwarded.

First to answer your question about neighbour - yes EIGRP send hellos to its neighbour at a regular interval. Hellos serve a number of purposes - one to make sure certain parameters are the same between both EIGRP neighbour - otherwise an adjacency will not be formed. An adjacency must be formed before routing info will be exchanged. The hellos are also used to detect loss of an neighbour.

So what you

router eigrp ! since most orgs do not have an AS number usually the number is set to 1 or 100

! all interfaces with IP address that fall into this range will run EIGRP

network ! as many network statements as required

passive-interface < interface> ! interfaces on which EIGRP is not to be used

eigrp log-neighbor-changes exit

There are other eigrp commands but you probably do not need to be concerend with them on T1 circuits

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Now things are beginning to make sense. A couple of questions:

- we actually have an AS number on our side, because we use BGP with our upstream providers. The other side doesn't have one. But we can just use any arbitrary number here, correct?

- including the statement 'variance 2' should cover our situation correct? The lower bandwithd link is more than half of the higher one.

- hello packets get sent out every interface unless listed in a passive-interface command, correct?

- I can get the EIGRP stanzas set up on both routers before taking out the static routes, to minimize downtime, correct?

Thanks for all of your help... it's greatly appreciated!


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correct but both sides must match for EIGRP



For example you would want to make the link to you ISP passive and also do not sent CDP to you ISP


static have an admin distance of 1 so they win over any other type other than connected

Just so you know you can also "float" statics so they are used unless a dynamic route is announced with a lower admin distance

ip route x.x.x.x m.m.m.m nh.nh.nh.nh 200 ! admin distance of 200 - this is a floating static route

On of the things to memorize or have handy is admin distance values see

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for example EIGRP internal routes have an admin distance of 90

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There seems to be some conspiracy between people with 2T1 lines one of which has 10 channels dedicated for voice - this is second case of this kind within past two weeks :-)

Look at this document

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Kind regards, iLya

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