I have got an odd Linux networking problem.

Two Linux boxes, called Dipsy and Vault (yes, really). Dipsy is an old, tired Redhat 7.1 machine, running on a Dell PII400. Vault is a much newer, Debian Sarge machine, running on a Via 500Mhz fanless box.

Vault can ping Dipsy perfectly. Dipsy can ssh to Vault without problem. All the other machines (Windows and Mac boxes) in the house can ssh and ping both boxes.

However, for some odd reason, Dipsy can't ping Vault properly. If you ping vault from Dipsy you get 80% or higher lost packets.

If you sniff the traffic between them you can see that Dipsy sends the requests and that Vault responds with the replies. For some reason that I can't fathom Dipsy doesn't see these replies.

Does anyone have any idea what is going on ?