I have the same problem here.
The server is Dell branded with BNX2 and Intel lan cards with Debian Lenny amd64. Both lan cards are connected to same lan switch with different IP addresses. The server works for some hours up to a few days. Then the entire network stack stops working. Even ping 127.0.0.1 does not work. But the network stack is the only thing that hangs. Processes are still running well. Memory ok, processor ok. I made a script that reboots the server, every time that it is not possible to check the remote LDAP server.
I have tested with different kernel versions. I tested with only Intel gigabit. I tested with only BNX2 gigabit.
No errors on dmesg. No erros on messages.
No idea about what could cause this.
Can we try to find common settings in order to find what is wrong?
Any help is welcome!