Cisco IOS Cookbook, 2nd Edition

Configuring Interpacket Delay

Problem

You want to slow down the rate that a router sends the packets in a single update to ensure that slower devices aren’t so overwhelmed that they lose information.

Solution

Use the output-delay configuration command to adjust the inter-packet delay of the RIP protocol:

Router2#configure terminal 
Enter configuration commands, one per line.  End with CNTL/Z.
Router2(config)#router rip
Router2(config-router)#output-delay 10
Router2(config-router)#exit
Router2(config)#end
Router2#

Discussion

If the routing table distributed in each update is small, it will fit into a single packet. But the maximum size for a RIP update packet is 512 bytes. Each packet has an 8-byte UDP header, and 4 bytes of general RIP information. The remaining 500 bytes of the packet carry the actual routes. Each individual route takes 20 bytes, so there can be at most 25 routes in one packet. If you have more than 25 routes in your routing table, RIP must send it as multiple packets.

The problem with this is that some devices can’t process large amounts of incoming routing information quickly, and they wind up missing some of the routing information. This is particularly true for older legacy equipment, or routers with slow processors or insufficient memory. So if you find that one or more of the neighboring routers has a mysteriously incomplete routing table, it might help to increase the interpacket spacing. The other reason for increasing the output-delay is to prevent bursts of RIP ...