This is a wired question but the participants here are so knowledgeable
I am sure this is old hat...
On a business trip I encountered a network where I was unable to log on
using my ThinkPad and the wired NIC. The network supposedly used DHCP
but my system was unable to obtain an IP address despite multiple
attempts, even after rebooting (also on different days). I eventually
was able to log on using a static IP address but also had supply the
DNS addresses as I was otherwise unable to surf the 'net. I should add
that this was an office network with many users and others temporarily
using it like myself had no problems with their Win systems.