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Port 109 (pop2)

IANA assigns port 109 to pop2: Post Office Protocol - Version 2.

Well-known (system) port, 0-1023 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
pop2 TCP Post Office Protocol - Version 2 Joyce K Reynolds -
pop2 UDP Post Office Protocol - Version 2 Joyce K Reynolds -

Check what is listening on port 109

Linux: is anything listening on TCP 109?
sudo ss -tlnp 'sport = :109'
Linux: UDP 109
sudo ss -ulnp 'sport = :109'
Linux / macOS: which process owns the port
sudo lsof -nP -i :109
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':109 '
Windows (Command Prompt)
netstat -ano | findstr :109
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 109 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 109
From Windows
Test-NetConnection HOST -Port 109
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 109

Block port 109 in the firewall

ufw
sudo ufw deny 109/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 109 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 109 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 109' -Direction Inbound -Protocol TCP -LocalPort 109 -Action Block
ufw
sudo ufw deny 109/udp
iptables
sudo iptables -A INPUT -p udp --dport 109 -j DROP
nftables
sudo nft add rule inet filter input udp dport 109 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 109' -Direction Inbound -Protocol UDP -LocalPort 109 -Action Block

Related ports

107rtelnet108snagas110POP3111rpcbind / portmapper

All port numbers · Open port checker
Assignment data: IANA port number registry (public domain), retrieved 2026-11-10.