Port 49 TACACS+ · TCP and UDP

What runs on port 49

TACACS+: Cisco's protocol for authenticating and authorising administrators on network devices, with per-command authorisation and accounting. It is the AAA protocol for device management, while RADIUS is used for network access. The body is encrypted with a shared key (weakly, by modern standards), so it belongs on the management network.

Software that uses it: Cisco ISE · tac_plus · FreeRADIUS (with TACACS+ module) · Aruba ClearPass

Should port 49 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.

• Keep it on the management VLAN and restrict by source address on the server.
• Use RADIUS (1812) for user network access and TACACS+ for device administration.

Check port 49

# on the host: is anything listening, and which process?
ss -ltnp 'sport = :49'
ss -lunp 'sport = :49'
sudo lsof -i :49

# from another machine: is it reachable?
nc -zv host 49
nmap -p 49 host
nc -zuv host 49
sudo nmap -sU -p 49 host
curl -v telnet://host:49      # 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 49

# ufw (Ubuntu/Debian)
sudo ufw allow from 10.0.0.0/8 to any port 49 proto tcp
sudo ufw allow from 10.0.0.0/8 to any port 49 proto udp
sudo ufw deny 49/tcp
sudo ufw deny 49/udp

# nftables
nft add rule inet filter input ip saddr 10.0.0.0/8 meta l4proto { tcp, udp } th dport 49 accept
nft add rule inet filter input meta l4proto { tcp, udp } th dport 49 drop

# iptables (legacy)
iptables -A INPUT -p tcp --dport 49 -s 10.0.0.0/8 -j ACCEPT
iptables -A INPUT -p tcp --dport 49 -j DROP
iptables -A INPUT -p udp --dport 49 -s 10.0.0.0/8 -j ACCEPT
iptables -A INPUT -p udp --dport 49 -j DROP

# firewalld
sudo firewall-cmd --permanent --add-rich-rule='rule family=ipv4 source address=10.0.0.0/8 port port=49 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 49" with no source is just "open".

Related ports

• 1812 RADIUS auth
• 1813 RADIUS accounting
• 22 SSH — SSH, SCP, SFTP, git over ssh

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