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Port 3750 (cbos-ip-port)

IANA assigns port 3750 to cbos-ip-port: CBOS/IP ncapsalation port.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
cbos-ip-port TCP CBOS/IP ncapsalation port Thomas Dannemiller -
cbos-ip-port UDP CBOS/IP ncapsalation port Thomas Dannemiller -

Registry dates for this port: registered 2003-04.

Check what is listening on port 3750

Linux: is anything listening on TCP 3750?
sudo ss -tlnp 'sport = :3750'
Linux: UDP 3750
sudo ss -ulnp 'sport = :3750'
Linux / macOS: which process owns the port
sudo lsof -nP -i :3750
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':3750 '
Windows (Command Prompt)
netstat -ano | findstr :3750
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 3750 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 3750
From Windows
Test-NetConnection HOST -Port 3750
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 3750

Block port 3750 in the firewall

ufw
sudo ufw deny 3750/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 3750 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 3750 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 3750' -Direction Inbound -Protocol TCP -LocalPort 3750 -Action Block
ufw
sudo ufw deny 3750/udp
iptables
sudo iptables -A INPUT -p udp --dport 3750 -j DROP
nftables
sudo nft add rule inet filter input udp dport 3750 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 3750' -Direction Inbound -Protocol UDP -LocalPort 3750 -Action Block

Related ports

3748webdata3749cimtrak3751gprs-cube3752vipremoteagent

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