Remember that we try to build this routing path from PC1: PC1 to R2 to R1 to R3 and last to PC2. You agree that the simple way is not to include R1 in this path…
To confirm our configuration using the CLI (Command Line Command), we check at R2 that PC2 network is reachable via R1 interface inter vlan204 network using the command show ip cef.
We check the same at R3 that PC1 network is reachable via the R1 interface in network 123.0.0.0.
A packet to reach PC2 from PC1 is first forwarded to R2 f1/1 interface in network 12.0.0.0. At R2, a route lookup is done against the destination of PC2. The configured static route is matched in this table and packet sent to the next hop. Cef forwarding confirms this routing. At R1, the packet is received and its destination looked up in the routing table and sent to R3 that forward it to PC2. The return traffic (reply) followers the same path…
Debug
let’s confirm our understanding of the operation of our setup using debug commands at each router. Let’s recall that the routing table called also local routing table or RIB (Routes Information Base) is different from Cef (Cisco Express Forwarding). Learnt routes are first put in routing table (RIB) and next in forwarding table (CEF). In CEF the forwarding that helps effectively send the packet is specified which is not necessary the case in routing table for the sample reason that forwarding a destination may require the usage of many routes to find the actual output interface. Think about routes that use an intermediate address as a nexthop (static routing, BGP, etc.). This intermediate address needs to be resolved to an output interface and IP in the same connected network before the routing is done, the new forwarding rule is added to CEF and packet sent…
