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Port 2551 (isg-uda-server)

IANA assigns port 2551 to isg-uda-server: ISG UDA Server.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
isg-uda-server TCP ISG UDA Server Dror Harari -
isg-uda-server UDP ISG UDA Server Dror Harari -

Check what is listening on port 2551

Linux: is anything listening on TCP 2551?
sudo ss -tlnp 'sport = :2551'
Linux: UDP 2551
sudo ss -ulnp 'sport = :2551'
Linux / macOS: which process owns the port
sudo lsof -nP -i :2551
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':2551 '
Windows (Command Prompt)
netstat -ano | findstr :2551
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 2551 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 2551
From Windows
Test-NetConnection HOST -Port 2551
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 2551

Block port 2551 in the firewall

ufw
sudo ufw deny 2551/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 2551 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 2551 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 2551' -Direction Inbound -Protocol TCP -LocalPort 2551 -Action Block
ufw
sudo ufw deny 2551/udp
iptables
sudo iptables -A INPUT -p udp --dport 2551 -j DROP
nftables
sudo nft add rule inet filter input udp dport 2551 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 2551' -Direction Inbound -Protocol UDP -LocalPort 2551 -Action Block

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