Why do some icmp replies follow shortest links and some follow routing? 1

[just1moretime]

5 Routers in a circle

R0- 1.1.1.0-R1- 2.2.2.0-R3- 3.3.3.0 -R4-4.4.4.0 - R0-5.5.5.0 (Router 0-1,2,3,4-Router 0)

R0 1.1.1.1 /24 ip route 0.0.0.0 0.0.0.0 1.1.1.2
5.5.5.2 /24

R1 1.1.1.2 /24 ip route 0.0.0.0 0.0.0.0 2.2.2.2
2.2.2.1 /24

R2 2.2.2.2 /24 ip route 0.0.0.0 0.0.0.0 3.3.3.2
3.3.3.1 /24

R3 3.3.3.2 /24 ip route 0.0.0.0 0.0.0.0 4.4.4.2
4.4.4.1 /24

R4 4.4.4.1 /24 ip route 0.0.0.0 0.0.0.0 5.5.5.2
5.5.5.1 /24

The problem:
A.When I ping from R0 to R1 1.1.1.2, appears to return icmp on 1.1.1.0 link. Direct link connect.
B.When I ping from R0 to R1 2.2.2.1, appears to return icmp on 1.1.1.0 link. Contrary to routing.
C.When I ping from R0 to R4 5.5.5.1, appears to return icmp on 5.5.5.0 link Direct link connect.
D.When I ping from R0 to R4 4.4.4.2, appears travel entire circle to R4, returns icmp back on 5.5.5.0 link.

To me, A is ok. B defies default routing. C is ok. Why doesnt D work like B

Thank you.

 

[imbadatthis]

for part b if you source your icmp from 5.5.5.2 to 2.2.2.1 it should travel the circle.
otherwise B knows how to get back to 1.1.1.1 through its own interface...



We must go always forward, not backward
always up, not down and always twirling twirling towards infinity.