From R1, when I traceroute to 8.8.8.8, the traffic goes to ASA --> EDGE Router1 --> and ISP.
But, when I do sh ip route on R1, it is learning default route from EDGE Router 2.
Shouldn’t the traffic goes to EDGE Router2 since 199.9.9.9 is the default gateway from R1?
Can EDGE-Router1 inspect the packet and see the destination and forward the packet based on EDGE-Router1’s routing table?
Hi @inyourname,
This is a great question and thanks for providing a diagram. There are some key points here to consider:
In IP routing, each device that received the packet will make its own decision on how to forward that packet. In your scenario when Edge Router 1 receives a packet destined for 8.8.8.8, it performs a lookup in its own routing table and forwards the packet direct to the ISP.
R1 is not able to dictate the routing decision on another router unless Source Routing (Source Routing as part of the Internet Protocol) is being used; this is very uncommon so we can ignore it.
R1 could influence the routing decisions made by another router by using a dynamic routing protocol to talk to another router, such as RIP, OSPF, BGP, IS-IS.
Also do note that R1 should not normally have a default route to a router outside its subnet.
I hope this helps. You might find it useful to review this [IP Routing Overview] (https://networklessons.com/cisco/ccna-routing-switching-icnd1-100-105/ip-routing-explained/) again and see if what I wrote makes sense. IP routing can be complicated but you are on the right track; thanks again for your question.
Kind regards,
Jon