Exchanging EIGRP topology information
 


EIGRP Update messages send topology information to neighbors.  These Update messages can be sent to multicast IP address 224.0.0.10 if the sending router needs to update multiple routers on the same subnet; otherwise, the updates are sent to the unicast IP address of the neighbor.  Hello messages are always sent to 224.0.0.10.  There is no concept of the OSPF Designated Router (DR) or Backup Designated Router (BDR), but the use of multicast packets on LANs allows EIGRP to exchange routing information with all neighbors on the LAN efficiently.

The update messages are sent using Reliable Transport Protocol (RTP).  RTP allows EIGRP to resend routing updates that are lost in transit.  This allows EIGRP to better avoid loops.

Neighbors use both full and partial routing updates.  A full update means that a router sends information about all known routes, whereas a partial update includes only information about recently changed routes.  Full updates occur when neighbors first come up.  After that, the neighbors send only partial updates in reaction to changes to a route.