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Port 131 (cisco-tna)

IANA assigns port 131 to cisco-tna: cisco TNATIVE.

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

IANA assignment

Service nameProtoDescriptionAssigneeReference
cisco-tna TCP cisco TNATIVE - -
cisco-tna UDP cisco TNATIVE - -

Check what is listening on port 131

Linux: is anything listening on TCP 131?
sudo ss -tlnp 'sport = :131'
Linux: UDP 131
sudo ss -ulnp 'sport = :131'
Linux / macOS: which process owns the port
sudo lsof -nP -i :131
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':131 '
Windows (Command Prompt)
netstat -ano | findstr :131
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 131 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 131
From Windows
Test-NetConnection HOST -Port 131
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 131

Block port 131 in the firewall

ufw
sudo ufw deny 131/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 131 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 131 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 131' -Direction Inbound -Protocol TCP -LocalPort 131 -Action Block
ufw
sudo ufw deny 131/udp
iptables
sudo iptables -A INPUT -p udp --dport 131 -j DROP
nftables
sudo nft add rule inet filter input udp dport 131 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 131' -Direction Inbound -Protocol UDP -LocalPort 131 -Action Block

Related ports

129pwdgen130cisco-fna132cisco-sys133statsrv

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