Hi,
RIPv2 works over UDP 520.
Layer2 Frame - IP Header (IP Protocol field=17) -- UDP (Dst port=520) --- RIP Payload.
IGRP, EIGRP and OSPF works over IP Layer. Each of that have got their own protocol value.
IGRP has got its own protocol value 9. So IGRP packet looks like below:
Layer2 Frame --- IP Header (IP Protocol field=9)--- IGRP payload.
EIGRP protocol value is 88. EIGRP packet
Layer2 Frame --- IP Header (IP Protocol field=88)--- EIGRP payload.
OSPF protocol value is 89. OSPF packet
Layer2 Frame --- IP Header (IP Protocol field=89)--- OSPF payload.
BGP works over TCP. The router which initiates BGP connection is client and the peer is server.
Layer2 Frame --- IP Header (IP Protocol field=6)---TCP (dst port=179) - BGP payload.
I do not exactly know why the protocols are working on these layers. RIP being a very primitive protocol, designers would have considered UDP would be sufficient. Moreover all the reliability mechanisms should be incorporated in the routing protocol design (different timers in RIP).
IGRP, EIGRP and OSPF works on above IP Layer where the designers would have had more modular in designing specific protocol characteristics.
I think BGP being works over IP (considers IP reachability is present before it starts) would have chosen TCP as it already have reliable delivery model. Moreover BGP itself is heavily loaded by carrying full internet feed, so it makes sense to offload reliable mechanisms to TCP. But these are my guesses.
thanks in advance
Arun
