In an Active Directory domain, domain controllers can be easily spotted depending on what services they host. Each service is usually accessible specific TCP and/or UDP port(s) making the DCs stand out in the network. Here is a list of ports to look for when hunting for domain controllers.
53/TCP and 53/UDP for DNS
88/TCP for Kerberos authentication
135/TCP and 135/UDP MS-RPC epmapper (EndPoint Mapper)
137/TCP and 137/UDP for NBT-NS
138/UDP for NetBIOS datagram service
139/TCP for NetBIOS session service
389/TCP for LDAP
636/TCP for LDAPS (LDAP over TLS/SSL)
445/TCP and 445/UDP for SMB
464/TCP and 445/UDP for Kerberos password change
3268/TCP for LDAP Global Catalog
3269/TCP for LDAP Global Catalog over TLS/SSL
The nmap utility can be used to scan for open ports in an IP range.
# -sS for TCP SYN scan# -n for no name resolution# --open to only show (possibly) open port(s)# -p for port(s) number(s) to scannmap-sS-n--open-p88,389 $IP_RANGE