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Port 7 (echo)

IANA assigns port 7 to echo: Echo.

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

IANA assignment

Service nameProtoDescriptionAssigneeReference
echo TCP Echo Jon Postel -
echo UDP Echo Jon Postel -

Check what is listening on port 7

Linux: is anything listening on TCP 7?
sudo ss -tlnp 'sport = :7'
Linux: UDP 7
sudo ss -ulnp 'sport = :7'
Linux / macOS: which process owns the port
sudo lsof -nP -i :7
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':7 '
Windows (Command Prompt)
netstat -ano | findstr :7
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 7 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 7
From Windows
Test-NetConnection HOST -Port 7
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 7

Block port 7 in the firewall

ufw
sudo ufw deny 7/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 7 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 7 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 7' -Direction Inbound -Protocol TCP -LocalPort 7 -Action Block
ufw
sudo ufw deny 7/udp
iptables
sudo iptables -A INPUT -p udp --dport 7 -j DROP
nftables
sudo nft add rule inet filter input udp dport 7 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 7' -Direction Inbound -Protocol UDP -LocalPort 7 -Action Block

Related ports

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