I Can Ping from One Machine but not from Another

[Sam]

I am a little confused about PING between a couple of machines on a network.
Here's what's going on...

Server
Address: 128.x.x.x

Computer 1 (Linux)
Address: 172.x.x.x (obviously on different subnet to Server)

Computer 2 (Win XP)
Address: 128.xx.x.x (different subnet to Server)

I am able to ping the Server from Computer 2.
I am able to ping Computer 1 from Computer 2.
Therefore, no problems pinging remote machines using Computer 2 (WinXP).

I am able to ping Computer 2 from Computer 1.
I am able to ping another Computer that is on the same subnet as the Server from Computer 1.
I am not able to ping Server from Computer 1. (100% Packet Loss)

How would I go about troubleshooting the ping problem from Computer 1 to the Server?

Could this be a routing problem? The Server has no software firewall blocking 172.x.x.x so I can count that out.

Any help is appreciated.

Thanks.

[Curt]

One thing I just noticed is there's no Default Gateway set on the Server. Will set it... but will be unable to do so for a couple of days. I'm thinking this might solve the issue?

[justin]

Can you ping PC1 from the server? Also try tracert in both directions.

It looks like the server does not know how to reach the 172.x.x.x subnet. Do a ROUTE PRINT on the server. See if there is a route to the 172 subnet.

The server gets the 4 ping packets. TCP/IP sees that the destination to send the return replies to is not the local subnet. It consults the routing table on how to reach this foreign subnet. If it can't tell by checking the route table, then the default action would be to send to the default gateway.

So I believe if it had a route to the 172 subnet, it would work even with no default gateway established.