how to prevent load balancing over frame relay links?

[crazyman143]

Hi, First of all I hope this is the right place to ask this. This isn't a question about a production network. This is just a problem I ran into while creating a packet tracer for my study of frame relay. Say I have the network below setup with point-to-point frame relay sub-interfaces. Each router is connected to every other router via a /30 subnet and subinterface as shown 

Now, I turned on EIGRP to share all networks between the routers. If I were to look at routing table for R3 for example, I see it learned 2 equal cost routes for the 10.1.1.0/30 network, because both R1 and R2 advertised it:

D 10.1.1.0 [90/2681856] via 10.1.1.10, 00:10:32, Serial2/0.302

  [90/2681856] via 10.1.1.5, 00:10:26, Serial2/0.301

If I ping 10.1.1.1 from R3, EIGRP will load balance it, because it thinks they are equal cost but in reality, half the packets go up to R2, and then get passed to R1 and back. All the routers will do this with the /30 subnets. hosts connected to the routers at each "location" probably wouldn't be trying to reach these subnets, but possibly eigrp traffic or something else might and would be traversing extra frame relay links unnecessarily right?

How is this delt with in the real world? Should load balancing just be disabled all together? or should costs be adjusted? what is best practice? sorry if this question is confusing. Thanks for any advice.

[nspasov]

Hi there, equal load balancing is a default feature of EIGRP and I would not recommend disabling it. What you can do instead is change one of the EIGRP metrics. This will result in higher (less preferred EIGRP metric), thus making the path less desirable. 

Changing the interface's delay and/or bandwidth would be the two easiest metrics to change. In general, it is recommended that you change the delay instead of the bandwidth (that way you won't affect QoS settings.)

I hope this helps! Here is some more info about EIGRP and its metric:

http://www.cisco.com/c/en/us/support/docs/ip/enhanced-interior-gateway-routing-protocol-eigrp/16406-eigrp-toc.html

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