I want to clear up something that has somewhat bothered me for a while now: "RTP" in EIGRP. RTP as referenced by EIGRP refers to Cisco's proprietary Reliable Transport Protocol, not the much more commonly discussed Real-time Transport Protocol characteristic of VoIP communications. This is an unfortunate collision of acronyms.
Reliable Transport Protocol (unlike VoIP's RTP) is not a wire-level protocol; rather, it simply provides sequencing and acknowledgment for EIGRP packets between neighbors. You can see Reliable Transport Protocol in action when observing any EIGRP adjacency (here's an example packet capture).
Sequence and acknowledgment numbers are used to provide ordering similar to TCP, but without any fancy windowing or congestion control (only one packet can be sent at a time). Additionally, hellos and explicit acknowledgments aren't transmitted reliably (they have no sequence number).