Links

Finding Domain Controllers and DHCP servers

nmap -sP <IP>/24 >> hosts.txt
nmap -p 389 <IP>
cat /var/lib/dhcp/*
cat /etc/resolve.conf
Route -n

Using Wireshark

If you find that your task is completely black boxed and a client won't give you a static IP to use then you can get on by stealing a valid users mac to then be in the mac pool and obtain a DHCP IP
Start Wireshark Search for a valid Mac (chose responsibly) Change your Mac to match Then disconnect and reconnect to the network, you should be given an IP