Recently i came across the issue which made my head turned to look at programming a protocol.
i was doing a RIP lab where i had to configure two router. Task was to identify the RIP version on 1st router and according to that configure the second router. So simply first though which came in my mind to identify a version of rip running on 1st router was ping to RIP multicast Address 126.96.36.199 and i did it.
But the result was totally unexpected to my cisco thinking. because i know which version i am running in 1st router i only configured it :-) WOW. but when i ping 188.8.131.52 1st router was replying i thought it might be possible just because of defult behavior of the RIP is to recieve v1 and v2 both. but when i configured the command version 1 under router rip which made it to pure RIP v1 router. Still after this configuration i was getting icmp reply from ist router to address 184.108.40.206
It mean RIP running router will always reply to multicast address 220.127.116.11 so this way of identification didn't work for me. I have to think something different which i can use to complete the task. i found out a very easy but working command which " debug ip rip event " This command will say which version of RIP update it is sending to media. wohho i was able to complete my rest of the Task. :-)