eigrp number of neighbors limitation

[dfulguer]

our WAN is connected via L2WAN and using EIGRP to connect the sites.  Currently there are 35 EIGRP neighbors over L2WAN and we are to install 15 more sites and will be connected to the same L2WAN.  Some sites are still using Cisco 2651XM and we would like to know if it can still handle another 15 EIGRP neighbors.  Some sites are 2800 and 2900 routers.  And is there any other things to consider for EIGRP over L2WAN?  Thank you.

[Vivek Ganapathi · Accepted solution]

There is no such limitations defined basically. But it totally depends on multiple factors like the amount of RAM + CPU processing power etc. I have seen some networks within around 90+ neighbors.

Vivek.

[dfulguer]

Hi Vivek, thank you.  The smallest/oldest router we have is Cisco 2651XM with 64M memory.  I guess it can still accommodate 15 more neighbors... how about the number of routes on the routing table? Any limitation for smaller routers?

[Vivek Ganapathi · Accepted solution]

Should be able to easily. There is no such limitations defined as i said. Prediction is highly difficult. But certain good practices would be to properly summarize the routes advertised. It's always better to keep the routing table less loaded.

[Peter Paluch · Accepted solution]

Hello,

I absolutely agree with Vivek. The principial limits of EIGRP, if there are any, highly exceed the limits of your platforms. You need to keep an eye on your RAM and CPU utilization. The show memory and show processes cpu sorted are your friends here. But personally, I see no issues with a 2651XM handling 50 EIGRP neighbors. It all depends on how much the router is loaded currently.

Other things to consider:

• Be careful properly setting the bandwidth command on your ports towards the L2WAN to realistically reflect the speed of the L2WAN. The main reason for doing this is the fact that EIGRP reserves up to 50% of interface bandwidth for its traffic. If the bandwidth command is not properly configured, EIGRP may either get choked or may overload the interface, leading to lost packets, retransmissions, neighbor flapping and SIA states. This document is a fine reading about these issues - while it talks about Frame Relay, the basic ideas stand.
• Load on devices may partially be decreased with judicious tuning of Hello/Hold timers.
• EIGRP Stub, summarization, distribution lists - they are all your friends and help you limit the query depth, decrease the amount of routing information, thereby decreasing load on your routers.

My two cents...

Best regards,

Peter

[dfulguer]

Thanks Guys... very much helpful.  Cheers