Apparently other people have experienced similar issues with the network locking up on some virtual machines after a period of time. I find the issue sometimes occurs when we kick off backups on soundwave and the network is placed under significant load.

Disabilng IPv6 is meant to solve the problem in some cases and I have high expectations that it'll help in our situation.

To disable IPv6 on Ubuntu 8.04.01 you need to add an entry to /etc/modprobe.d/blacklist containing the following:

# blacklist IPv6
blacklist ipv6

You'll then need to reboot the machine, and confirm that the module has not been loaded.

mlambie@soundwave:~$ sudo lsmod | grep ipv6
mlambie@soundwave:~$ sudo ip a | grep inet6

Both tests should return nothing, confirming that the module is not active.