What port does SNMP use?
SNMP uses port 161 over UDP.
| Port | Protocol | Name | What it is for |
|---|---|---|---|
| 161 | UDP | SNMP | Network device monitoring and management. |
What catches people out
SNMP v1 and v2c authenticate with a community string sent in clear text, and "public" is still a common default. Use v3, or firewall it to the monitoring host.
Checking it is listening
sudo lsof -i :161 # macOS, Linux
netstat -ano | findstr :161 # Windows
nc -zuv host 161 # from elsewhere (-u because this is UDP)An "address already in use" error on a port nothing appears to be holding usually means the socket is in TIME_WAIT rather than that a process has it — the ports reference covers that and the ephemeral range.
Frequently asked questions
What port does SNMP use?
SNMP uses port 161 over UDP. Network device monitoring and management.
What should I watch out for with port 161?
SNMP v1 and v2c authenticate with a community string sent in clear text, and "public" is still a common default. Use v3, or firewall it to the monitoring host.
How do I check whether SNMP is listening?
sudo lsof -i :161 on macOS or Linux, netstat -ano | findstr :161 on Windows. From another machine, nc -zuv host 161 says whether anything answers.
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