RIP: routing by rumour

The idea

officeRouter, coreRouter and branchRouter, three routers in a triangle, find their routes with RIP: each tells its neighbours what it can reach and how far. A laptop in the office reaches a web server at the branch; good news spreads fast, bad news slowly.

Steps

1. Routes by hop count

   Read officeRouter's RIP table, then trace the laptop's way to the web server. Nobody typed these routes: the routers told each other, so the table shows who said what and how far away it is.

   officeRouter:~# vtysh
   laptop:~# traceroute -n -q1 -w2 10.0.3.10

2. Telling the neighbours, every 5 seconds

   Each router sends its whole table to its neighbours on a timer. Record coreRouter's updates on officeRouter for 12 seconds. Repeating it all, changed or not, is how a quiet neighbour gets noticed.

   officeRouter:~# timeout 12 tcpdump -n -v -i officeToCore udp port 520 and src 10.0.12.3