eigrp

[bericaleb]

Why does my Cisco 3662,3841, catalyst 3750s send EIGRP information to address 224.0.0.10?

[Richard Burts]

Bernadette

This is because part of the specification of the EIGRP routing protocol is that it sends routing updates using multicast address 224.0.0.10. This is similar to how OSPF sends updates to multicast addresses of 224.0.0.5 and 224.0.0.6.

HTH

Rick

[bericaleb]

Hi

is this a good thing for the Ethernet LAN? Does it causes congestion on the network?

[Jon Marshall · Accepted solution]

No it won't cause congestion on a LAN as it really doesn't account for much of the traffic you will see on a LAN.

What should be said is that even though it is a multicast address all devices, routers, PC's, servers, on that subnet will see the update.

HTH

Jon

[bericaleb]

thanks. Solved my question.

[jlhainy]

If it bothers you to have eigrp packets multicasted onto your LAN, you can stop that from happening by using the passive-interface command on your eigrp AS statement in your config.

[bericaleb]

hi

What does this command do exactly? What are the impact of using this command. How do we configure this command?

[Jon Marshall · Accepted solution]

Hi

The passive-interface command stops hello packets being exchanged between EIGRP neighbours. This means a neighborship si not formed and so no routing updates are sent or received.

You configure it under your router eigrp section eg

router eigrp 1

passive-interface fa0/1

This means any other EIGRP routers on the subnet that fa0/1 connects to will not exchange hellos with this router and hence no neighborship is formed.

The impact of using this command is that you have just stopped the router receiving routing updates and sending routing updates on it's fa0/1 interface. This may well result in an incomplete routing table.

Attached is a link to a doc about use of passive-interface in EIGRP.

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080093f0a.shtml

HTH

Jon

[Jon Marshall]

Hi

EIGRP uses the multicast address 224.0.0.10 to communicate with any other EIGRP speaking routers on the network. It is the way the routing protocol has been written. It is not unique in using multicast addressing eg

OSPF uses

224.0.0.5 = all OSPF routers

224.0.0.6 = DR/DBR

HTH

Jon

[jbrunner007]

to actually get the behavior where eigrp uses unicast, and not multicast you need the

neighbor x.x.x.x under the eigrp process.

If you do this the interface on which this neighbor can be found switches from using multicast to unicast.