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Port 3742 (cst-port)

IANA assigns port 3742 to cst-port: CST - Configuration & Service Tracker.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
cst-port TCP CST - Configuration & Service Tracker Hai Ou Yang -
cst-port UDP CST - Configuration & Service Tracker Hai Ou Yang -

Registry dates for this port: registered 2003-04.

Check what is listening on port 3742

Linux: is anything listening on TCP 3742?
sudo ss -tlnp 'sport = :3742'
Linux: UDP 3742
sudo ss -ulnp 'sport = :3742'
Linux / macOS: which process owns the port
sudo lsof -nP -i :3742
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':3742 '
Windows (Command Prompt)
netstat -ano | findstr :3742
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 3742 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 3742
From Windows
Test-NetConnection HOST -Port 3742
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 3742

Block port 3742 in the firewall

ufw
sudo ufw deny 3742/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 3742 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 3742 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 3742' -Direction Inbound -Protocol TCP -LocalPort 3742 -Action Block
ufw
sudo ufw deny 3742/udp
iptables
sudo iptables -A INPUT -p udp --dport 3742 -j DROP
nftables
sudo nft add rule inet filter input udp dport 3742 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 3742' -Direction Inbound -Protocol UDP -LocalPort 3742 -Action Block

Related ports

3740heartbeat3741wysdma3743ipcs-command3744sasg

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