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Port 3343 (ms-cluster-net)

IANA assigns port 3343 to ms-cluster-net: MS Cluster Net.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
ms-cluster-net TCP MS Cluster Net David Dion -
ms-cluster-net UDP MS Cluster Net David Dion -

Registry dates for this port: registered 2009-02-12.

Check what is listening on port 3343

Linux: is anything listening on TCP 3343?
sudo ss -tlnp 'sport = :3343'
Linux: UDP 3343
sudo ss -ulnp 'sport = :3343'
Linux / macOS: which process owns the port
sudo lsof -nP -i :3343
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':3343 '
Windows (Command Prompt)
netstat -ano | findstr :3343
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 3343 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 3343
From Windows
Test-NetConnection HOST -Port 3343
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 3343

Block port 3343 in the firewall

ufw
sudo ufw deny 3343/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 3343 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 3343 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 3343' -Direction Inbound -Protocol TCP -LocalPort 3343 -Action Block
ufw
sudo ufw deny 3343/udp
iptables
sudo iptables -A INPUT -p udp --dport 3343 -j DROP
nftables
sudo nft add rule inet filter input udp dport 3343 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 3343' -Direction Inbound -Protocol UDP -LocalPort 3343 -Action Block

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Assignment data: IANA port number registry (public domain), retrieved 2026-11-10.