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Port 3757 (grf-port)

IANA assigns port 3757 to grf-port: GRF Server Port.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
grf-port TCP GRF Server Port Robert Banfill -
grf-port UDP GRF Server Port Robert Banfill -

Registry dates for this port: registered 2003-04.

Check what is listening on port 3757

Linux: is anything listening on TCP 3757?
sudo ss -tlnp 'sport = :3757'
Linux: UDP 3757
sudo ss -ulnp 'sport = :3757'
Linux / macOS: which process owns the port
sudo lsof -nP -i :3757
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':3757 '
Windows (Command Prompt)
netstat -ano | findstr :3757
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 3757 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 3757
From Windows
Test-NetConnection HOST -Port 3757
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 3757

Block port 3757 in the firewall

ufw
sudo ufw deny 3757/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 3757 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 3757 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 3757' -Direction Inbound -Protocol TCP -LocalPort 3757 -Action Block
ufw
sudo ufw deny 3757/udp
iptables
sudo iptables -A INPUT -p udp --dport 3757 -j DROP
nftables
sudo nft add rule inet filter input udp dport 3757 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 3757' -Direction Inbound -Protocol UDP -LocalPort 3757 -Action Block

Related ports

3755sas-remote-hlp3756canon-capt3758apw-registry3759exapt-lmgr

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