I have a server which I've been using at home (with no problems) for about a year. I recently upgraded the memory from 2x2GB to 2x4GB and updated the operating system to ubuntu server 11.10. Following this I have network problems with the server after a few minutes. For example, if I log in immediately after power up and run ping, I get the following output

$ ping
64 bytes from icmp_req=1 ttl=64 time=0.516 ms
64 bytes from icmp_req=46 ttl=64 time=0.488 ms
64 bytes from icmp_req=47 ttl=64 time=23789 ms
from icmp_seq=123 Destination Host Unreachable
from icmp_seq=129 Destination Host Unreachable

where is my home router. All the other computers on the network are fine so the problem seems to be with the server. I've tried searching around for a fix but I've yet to find anything helpful. Part of the problem is that I'm not sure what could cause such behaviour. Does anyone have any ideas? Thanks