With EIGRP, can you load balance between a serial and fastethernet connection?

StonedHitman

So, i was making a small lab in packet tracer that I can later put into my real lab. I used 2 routers and a multilayer switch to act as a 3rd router. I connect a PC to a L2 switch, that switch connects to my MLS and a router. Then my second router connects to the MLS and first router(this one is using serial) across from my PC. I configure EIGRP and everything pings and works fine, but on the second router when I do a sh ip route and sh ip eigrp topology, I only see the route going over the serial link and not the route going over the ethernet link. However, it does show that route going over the ethernet link only when my serial link goes down. Also, my MLS can load balance just fine across it's two ethernet links. This leads me to believe that a router can't load balance between serial and ethernet, but I want to be 100% sure.

Sorry, I would put up an attachment showing my topology but for some reason the image is way too small.

Jon_Cisco

I"m guessing that it is not equal cost so it does not load balance by default.
I think you can set up unequal cost load balancing. At least it's something to look into for your question.

StonedHitman

Weird, I just did the exact same setup on my physical lab and it shows the route going over the faster ethernet link and both routes show in the topology table. Must be a bug with PT

theodoxa

EIGRP supports unequal cost load balancing using the variance command. I don't see why it wouldn't load balance over both if the variance was sufficient.

Heero

StonedHitman wrote: »

Weird, I just did the exact same setup on my physical lab and it shows the route going over the faster ethernet link and both routes show in the topology table. Must be a bug with PT

The topology table is not the routing table. The routing table only contains the routes that are actively used by the router. The topology table contains successor and feasible successor routes. A feasible successor is not the best route to a destination, but it is guaranteed to be loop free which makes it valid, just not the best route.

By default, EIGRP only does load balancing on equal cost routes, referred to as ECMP (Equal Cost Multiple Path or something like that). So two or more routes will need to have the same feasible distance to be load balanced.

You can modify the variance command under the EIGRP process to cause unequal cost load balancing between multiple routes that show up in the EIGRP topology table. By default the variance multiplier is 1, so it will only do equal cost load balancing. If you set it higher, it can do unequal cost load balancing (remember that it is only between routes in the EIGRP topology table, successors and feasible successors only).

Scorp6

Heero wrote: »

The topology table is not the routing table. The routing table only contains the routes that are actively used by the router. The topology table contains successor and feasible successor routes. A feasible successor is not the best route to a destination, but it is guaranteed to be loop free which makes it valid, just not the best route.

By default, EIGRP only does load balancing on equal cost routes, referred to as ECMP (Equal Cost Multiple Path or something like that). So two or more routes will need to have the same feasible distance to be load balanced.

You can modify the variance command under the EIGRP process to cause unequal cost load balancing between multiple routes that show up in the EIGRP topology table. By default the variance multiplier is 1, so it will only do equal cost load balancing. If you set it higher, it can do unequal cost load balancing (remember that it is only between routes in the EIGRP topology table, successors and feasible successors only).

This. If the variance 2 command is used in the router eigrp process, the router will load balance over multiple routes (defaulted to max of 4 if I recall correctly, up to a max of 16) as long as those other routes are less than 2 times the feasible distance of the successor route. If variance 3 is used, the router will load balance over the routes that have a feasible distance less than 3 times the feasible distance of the successor, etc.

Ryuksapple84

Why not load balance with glbp or hsrp instead?

networker050184

Load balancing with a routing protocol and a first hop redundancy protocol serve completely different purposes. Not to mention you can't run either of those on a serial connection.