Port 389 LDAP · TCP and UDP

What runs on port 389

LDAP: the directory protocol behind Active Directory, FreeIPA, OpenLDAP and most "log in with your company account" setups. Port 389 is plaintext with optional STARTTLS; 636 is LDAPS. Binds (logins) over plain 389 send the password in the clear, which Windows now rejects by default (LDAP signing/channel binding).

Software that uses it: Active Directory · OpenLDAP · FreeIPA / 389 Directory Server · Samba AD · Okta/Entra LDAP interfaces

Should port 389 be open?

Private network or VPN only. Nothing good comes from this port being reachable from the internet. Keep it on an internal network, reach it over a VPN or an SSH tunnel, and firewall it from everything that does not need it.

• ldapsearch -ZZ forces STARTTLS and fails loudly if it is not available.
• Global Catalog in AD is on 3268/3269, not 389, for forest-wide searches.

Check port 389

# on the host: is anything listening, and which process?
ss -ltnp 'sport = :389'
ss -lunp 'sport = :389'
sudo lsof -i :389

# from another machine: is it reachable?
nc -zv host 389
nmap -p 389 host
nc -zuv host 389
sudo nmap -sU -p 389 host
curl -v telnet://host:389      # raw TCP connect test, Ctrl-C to leave

A port that answers from the internet when it should not is the finding; nmap from a machine outside your network (or a VPS) is the honest test, because scans from inside the LAN pass the firewall you are trying to verify.

Allow or block port 389

# ufw (Ubuntu/Debian)
sudo ufw allow from 10.0.0.0/8 to any port 389 proto tcp
sudo ufw allow from 10.0.0.0/8 to any port 389 proto udp
sudo ufw deny 389/tcp
sudo ufw deny 389/udp

# nftables
nft add rule inet filter input ip saddr 10.0.0.0/8 meta l4proto { tcp, udp } th dport 389 accept
nft add rule inet filter input meta l4proto { tcp, udp } th dport 389 drop

# iptables (legacy)
iptables -A INPUT -p tcp --dport 389 -s 10.0.0.0/8 -j ACCEPT
iptables -A INPUT -p tcp --dport 389 -j DROP
iptables -A INPUT -p udp --dport 389 -s 10.0.0.0/8 -j ACCEPT
iptables -A INPUT -p udp --dport 389 -j DROP

# firewalld
sudo firewall-cmd --permanent --add-rich-rule='rule family=ipv4 source address=10.0.0.0/8 port port=389 protocol=tcp accept'

Replace 10.0.0.0/8 with the networks that need access. Allowing by source address is the rule that matters; "allow 389" with no source is just "open".

Related ports

• 636 LDAPS — LDAP over TLS
• 88 Kerberos — Authentication (Active Directory)
• 3268 AD Global Catalog — 3269 over TLS

Part of the port number reference. Ports are 16-bit numbers; see also the subnet calculator and the packet decoder, which shows ports inside TCP and UDP headers.

Questions