Strange Ping Problem

Now i am sure i have seen this before but its a little fuzzy. I was wondering if anyone has come across this problem and can explain it ?

We have host A and host B. Now, A & B are seperated by loads of routers to route the traffic between them both. If you ping from A to B, you get replies. If you ping from B to A, you don't get anything. (no firewalls or access-list in the path)

Now i am a little confussed and wondered if anyone has ever experienced something similar ?

Cheers

Only when one of the 2 machines have a personal firewall (like WinXP firewall) ON and the other doesn't, I see such things.

Thanks for the reply but i am being told that there are no firewalls in between the machines.

Smurf, do the pings time out or do you get something along the lines of "destination host (or net) unreachable"? Are the two machines able to communicate with each other in any other form? What does a tracert command reveal when ran from host B to A?

There is a network in my work place....and the computers in the network are able to access external sites such as Google, Yahoo, etc, but they cannot ping any, the requests time out. I was told by the network guys that that is how the firewall that they are going through is configured.

K

hi smurf.........
try this command on router B #clear arp cahce.
this will happen sometimes bcuase of leased line connection.Clear the arp entries and try to ping........

The other things that can cause this kind of thing are:
1) incorrect subnet mask on the remote machine
2) asymmetric routing or similar routing table anomaly at one end or the other