Solved: Too many EIGRP routes!

CriscoSystems · ‎05-07-2009

According to my BSCI study materials, the EIGRP topology table can store up to six redundant routes.

What if, bizarrely, there are more than six routes to a destination and all the metrics are equal?

I'm guessing it would just install the first six it learns about; but that makes me wonder about the architecture of the EIGRP software: How long does it take for a received update to be examined and installed in the topo table? Can another update arrive and compete with it before the topology table is officially updated?

Giuseppe Larosa · ‎05-07-2009

Hello Stuey,

>> Can another update arrive and compete with it before the topology table is officially updated?

Very good note this.

Actually, in the DUAL algorithm description it is clearly stated that each input event (EIGRP hello, EIGRP update and so on) is processed one at time.

They are totally processed one each.

So the condition you have suggested should not happen regardless of the time it takes to complete the process actions on the update.

So you can say that the updates coming from the 6 oldest neighbors are installed.

Actually sh ip eigrp neighbors contains a column H that tells the order of neighborship (H=0 oldest)

Note:

newer IOS images can have increased to 8 this limit reflecting the increased paths in CEF.

Hope to help

Giuseppe

View solution in original post

Giuseppe Larosa · ‎05-07-2009

Hello Stuey,

>> Can another update arrive and compete with it before the topology table is officially updated?

Very good note this.

Actually, in the DUAL algorithm description it is clearly stated that each input event (EIGRP hello, EIGRP update and so on) is processed one at time.

They are totally processed one each.

So the condition you have suggested should not happen regardless of the time it takes to complete the process actions on the update.

So you can say that the updates coming from the 6 oldest neighbors are installed.

Actually sh ip eigrp neighbors contains a column H that tells the order of neighborship (H=0 oldest)

Note:

newer IOS images can have increased to 8 this limit reflecting the increased paths in CEF.

Hope to help

Giuseppe

Harold Ritter · ‎05-08-2009

Giuseppe,

Just as an additional piece of information, recent IOS trains have increased that limit beyond 8 equal cost paths. 12.4T and 12.2SRx for instance have a limit of 32 as shown below.

R1(config-router)#maximum-paths ?

<1-32> Number of paths

Regards

Harold Ritter
Sr Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México

Giuseppe Larosa · ‎05-10-2009

Hello Harold,

you are wellcome as usual

I had heard of 16 paths.

Best Regards

Giuseppe