Port 161 – SNMP Protocol Specification

Technical analysis, security advisories, vulnerability mitigation, and firewall syntax for TCP/UDP port 161 (SNMP).

Port Number 161

Transport Protocol UDP

Port Range Type Well-Known (0-1023)

Default Status Restricted / LAN

Service Description & Architectural Context

Simple Network Management Protocol agent query endpoint.

IANA / RFC Designation:

Port 161 is assigned to SNMP under the Internet Assigned Numbers Authority (IANA) service name registry. In enterprise infrastructure and homelab setups, services listening on this port must follow the principle of least privilege.

Security Analysis & Attack Surface Assessment

SNMP v1/v2c send community strings in plaintext. Always use SNMPv3 with AES.

Hardening Recommendations:

Do not expose port 161 to public WAN interfaces unless authenticated TLS or VPN wrapping is strictly enforced.
Enforce rate-limiting using Fail2ban, CrowdSec, or cloud edge DDoS protection.
Audit active listening sockets locally: ss -tulpn | grep :161 or netstat -ano | findstr :161.

Firewall Rule Snippets for Port 161

UFW (Ubuntu / Debian Linux)

sudo ufw allow 161/udp

iptables (Standard Linux Kernel)

sudo iptables -A INPUT -p udp --dport 161 -j ACCEPT

Windows PowerShell (Defender Advanced Firewall)

New-NetFirewallRule -DisplayName "Allow Port 161" -Direction Inbound -LocalPort 161 -Protocol UDP -Action Allow

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