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New Member

RIP/EIGRP maximum number of Equal cost routes

I am looking for documentation on:

If a router has 20 equal cost routing paths and only 4 show up in the routing table, what is the determining factor that chooses which four and where are the other 16 put in case the 4 routes become unusable.

Most documentation will tell you the maximum amount and how to change it but I have not found any documentation on how EIGRP or RIP chooses the routes.

6 REPLIES
New Member

Re: RIP/EIGRP maximum number of Equal cost routes

I would believe that all the routes that it recieved are stored in memory. I know for bgp it's sh ip bgp will so you all the routes that it's recieved. I don't have a router running rip or eigrp to give it a try on.

New Member

Re: RIP/EIGRP maximum number of Equal cost routes

EIGRP can have only 4 paths to a destination. The admin distance is considered first and if they are same then then metric is considered.

http://www.cisco.com/warp/customer/105/46.html

ofcourse if both admin distance and metric is the same, i am not sure what other parameter it will use or may be just choose the first 4 it learned. I am not sure.

Gold

Re: RIP/EIGRP maximum number of Equal cost routes

You can have up to 4 by default, but you can configure the routing table to accept up to 6 on older code, and up to 8 on newer code, using the command "maximum-paths" under router eigrp. EIGRP will attempt to install all of the available paths, but the routing table will only allow it to install the first x that it installs.

The routes which are not installed by EIGRP are placed in a "backup table." If one route fails, each routing protocol running on the router is notified, and will attempt to install any routes (which match the destination, of course) back into the routing table. Again, the frst x paths would win.

Be careful with this much redundancy in eigrp--you're playing with fire if you have 15 or 20 links between a pair of routers.Russ

New Member

Re: RIP/EIGRP maximum number of Equal cost routes

hello!

"If multiple paths have the same metric, a maximum of 16 can be installed in the routing table, and the router can

perform load balancing between them. EIGRP can also perform load balancing between unequal-cost paths."

"Note Before Cisco IOS Release 12.3(2)T, the maximum number of parallel routes (equalcost paths)

supported by IP routing protocols was 6; in Cisco IOS Release 12.3(2)T that maximum was changed to 16."

from book: Implementing Cisco IP Routing (ROUTE) Foundation Learning Guide for the ROUTE 642-902

by Teare Diane

tryed in GNS3 to simulate ... !

Hall of Fame Super Gold

Re: RIP/EIGRP maximum number of Equal cost routes

Just to let you know, you're responding to an 11 years old thread, since then people have long moved on.

New Member

RIP/EIGRP maximum number of Equal cost routes

Hello Paolo!

You are right !

I was concentrated on the broblem and I  miss this ....

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