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Port 675 (dctp)

IANA assigns port 675 to dctp: DCTP.

Well-known (system) port, 0-1023 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
dctp TCP DCTP Andre Kramer -
dctp UDP DCTP Andre Kramer -

Check what is listening on port 675

Linux: is anything listening on TCP 675?
sudo ss -tlnp 'sport = :675'
Linux: UDP 675
sudo ss -ulnp 'sport = :675'
Linux / macOS: which process owns the port
sudo lsof -nP -i :675
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':675 '
Windows (Command Prompt)
netstat -ano | findstr :675
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 675 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 675
From Windows
Test-NetConnection HOST -Port 675
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 675

Block port 675 in the firewall

ufw
sudo ufw deny 675/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 675 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 675 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 675' -Direction Inbound -Protocol TCP -LocalPort 675 -Action Block
ufw
sudo ufw deny 675/udp
iptables
sudo iptables -A INPUT -p udp --dport 675 -j DROP
nftables
sudo nft add rule inet filter input udp dport 675 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 675' -Direction Inbound -Protocol UDP -LocalPort 675 -Action Block

Related ports

673cimplex674acap676vpps-via677vpp

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