eigrp rtp...

this one never goes away...

http://insearchofthecert.blogspot.com/2012/11/rtp-in-eigrp.html

In order to ensure that routing updates and queries are not lost, we need a way to make certain other routers have received these multicast packets intact and to recover from errors if they haven’t. For these reasons, updates and queries are handled by the reliable multicast transport in EIGRP.

like ospf, eigrp uses a protocol, 88 (ospf uses 89) and unlike bgp which uses tcp port 179...

these numbers are often referred to as ports in ospf and eigrp... they are protocols, not tcp or udp ports...

then of course, wendell has his say...

 RTP allows the Updates to be sent as multicasts. If any neighbors fail to acknowledge receipt of the multicasted update, RTP resends Updates as unicasts just to those neighbors.

this is a fine point, but russ and wendell appear to be agreeing here; differently...

 http://www.iana.org/assignments/protocol-numbers/protocol-numbers.xml