Port 749 Kerberos admin · TCP and UDP

What runs on port 749

Kerberos administration (kadmin): principal and policy management for MIT and Heimdal KDCs. Admin-only; restrict to admin hosts.

Software that uses it: MIT kadmind · Heimdal kadmind · FreeIPA

Should port 749 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.

• Not used by Active Directory, which manages principals over LDAP.

Check port 749

# on the host: is anything listening, and which process?
ss -ltnp 'sport = :749'
ss -lunp 'sport = :749'
sudo lsof -i :749

# from another machine: is it reachable?
nc -zv host 749
nmap -p 749 host
nc -zuv host 749
sudo nmap -sU -p 749 host
curl -v telnet://host:749      # 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 749

# ufw (Ubuntu/Debian)
sudo ufw allow from 10.0.0.0/8 to any port 749 proto tcp
sudo ufw allow from 10.0.0.0/8 to any port 749 proto udp
sudo ufw deny 749/tcp
sudo ufw deny 749/udp

# nftables
nft add rule inet filter input ip saddr 10.0.0.0/8 meta l4proto { tcp, udp } th dport 749 accept
nft add rule inet filter input meta l4proto { tcp, udp } th dport 749 drop

# iptables (legacy)
iptables -A INPUT -p tcp --dport 749 -s 10.0.0.0/8 -j ACCEPT
iptables -A INPUT -p tcp --dport 749 -j DROP
iptables -A INPUT -p udp --dport 749 -s 10.0.0.0/8 -j ACCEPT
iptables -A INPUT -p udp --dport 749 -j DROP

# firewalld
sudo firewall-cmd --permanent --add-rich-rule='rule family=ipv4 source address=10.0.0.0/8 port port=749 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 749" with no source is just "open".

Related ports

• 88 Kerberos — Authentication (Active Directory)
• 464 Kerberos passwd

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