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Port 3131 (netbookmark)

IANA assigns port 3131 to netbookmark: Net Book Mark.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
netbookmark TCP Net Book Mark Yiftach Ravid -
netbookmark UDP Net Book Mark Yiftach Ravid -

Check what is listening on port 3131

Linux: is anything listening on TCP 3131?
sudo ss -tlnp 'sport = :3131'
Linux: UDP 3131
sudo ss -ulnp 'sport = :3131'
Linux / macOS: which process owns the port
sudo lsof -nP -i :3131
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':3131 '
Windows (Command Prompt)
netstat -ano | findstr :3131
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 3131 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 3131
From Windows
Test-NetConnection HOST -Port 3131
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 3131

Block port 3131 in the firewall

ufw
sudo ufw deny 3131/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 3131 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 3131 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 3131' -Direction Inbound -Protocol TCP -LocalPort 3131 -Action Block
ufw
sudo ufw deny 3131/udp
iptables
sudo iptables -A INPUT -p udp --dport 3131 -j DROP
nftables
sudo nft add rule inet filter input udp dport 3131 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 3131' -Direction Inbound -Protocol UDP -LocalPort 3131 -Action Block

Related ports

3129netport-id3130icpv23132ms-rule-engine3133prism-deploy

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