Port 162 SNMP trap · UDP

What runs on port 162

SNMP traps and informs: devices push alerts (link down, high temperature, power supply failed) to a manager listening on 162, instead of waiting to be polled. Traps are fire-and-forget UDP; informs are acknowledged.

Software that uses it: snmptrapd · Zabbix · LibreNMS · SolarWinds

Should port 162 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.

• Traps need the manager's address configured on every device; test with snmptrap from a host first.

Check port 162

# on the host: is anything listening, and which process?
ss -lunp 'sport = :162'
sudo lsof -i :162

# from another machine: is it reachable?
nc -zuv host 162
sudo nmap -sU -p 162 host

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 162

# ufw (Ubuntu/Debian)
sudo ufw allow from 10.0.0.0/8 to any port 162 proto udp
sudo ufw deny 162/udp

# nftables
nft add rule inet filter input ip saddr 10.0.0.0/8 udp dport 162 accept
nft add rule inet filter input udp dport 162 drop

# iptables (legacy)
iptables -A INPUT -p udp --dport 162 -s 10.0.0.0/8 -j ACCEPT
iptables -A INPUT -p udp --dport 162 -j DROP

# firewalld
sudo firewall-cmd --permanent --add-rich-rule='rule family=ipv4 source address=10.0.0.0/8 port port=162 protocol=udp accept'

Replace 10.0.0.0/8 with the networks that need access. Allowing by source address is the rule that matters; "allow 162" with no source is just "open".

Related ports

• 161 SNMP — Network monitoring
• 514 syslog — Remote logging (tcp 514 is rsh/rlogin historically)

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