Port 161 — SNMP

Security guidance

Public SNMP with the default "public" community string leaks your entire network inventory. Keep it on a management VLAN.

Test port 161 yourself

From your own machine, against any host (swap in your domain):

macOS / Linux — netcat

nc -vz example.com 161

Any OS — nmap

nmap -p 161 example.com

Windows — PowerShell

Test-NetConnection example.com -Port 161

open = a service answered on port 161; closed = the host replied but nothing is listening; filtered = a firewall silently dropped the probe. These test from your network — our port checker tests from the outside, the view that matters for security.

Other common ports