A packet traverses from a source to a destination in one path and takes a different path when it returns to the source. This is commonly seen in Layer-3 routed networks.
In this asymmetrical scenario R1 still receive the reply from R4 (188.8.131.52), which means there will be no issue and also because router do not care about the session state like firewalls do.
What would be the issue? There’s Firewall going back (return path) and it’s not in the state table of the firewall meaning firewall doesn’t know about the connection or request.
Solution: Modify the route for the return traffic.
1. From source to destination and then from destination to source.
2. Do extended ping w/ record option. (9hops Only)