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Port 3400 (csms2)

IANA assigns port 3400 to csms2: CSMS2.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
csms2 TCP CSMS2 Markus Michels 2 -
csms2 UDP CSMS2 Markus Michels 2 -

Check what is listening on port 3400

Linux: is anything listening on TCP 3400?
sudo ss -tlnp 'sport = :3400'
Linux: UDP 3400
sudo ss -ulnp 'sport = :3400'
Linux / macOS: which process owns the port
sudo lsof -nP -i :3400
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':3400 '
Windows (Command Prompt)
netstat -ano | findstr :3400
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 3400 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 3400
From Windows
Test-NetConnection HOST -Port 3400
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 3400

Block port 3400 in the firewall

ufw
sudo ufw deny 3400/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 3400 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 3400 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 3400' -Direction Inbound -Protocol TCP -LocalPort 3400 -Action Block
ufw
sudo ufw deny 3400/udp
iptables
sudo iptables -A INPUT -p udp --dport 3400 -j DROP
nftables
sudo nft add rule inet filter input udp dport 3400 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 3400' -Direction Inbound -Protocol UDP -LocalPort 3400 -Action Block

Related ports

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