I've discovered an "unwanted behavior" (bug I think) when you switch from static to DHCP address; step to reproduce:
1. Send a sketch to Galileo with Ethernet.begin(mac, ip) (static address)
2. Galileo has the right (static) IP
3. Modify the sketch to use DHCP (eg. remove ip parameter) and send it to Galileo
4. Galileo starts the sketch and still use the old (static) IP address
4a. You can resend the sketch more and more, but still...
5. Cold reboot Galileo (unplug USB, unplug power, plug power, plug USB, resend sketch) and now DHCP works
I don't have any Wireshark capture right now. I suppose that Galileo isn't requesting DHCP address on step 4 even if it's istructed to do so.