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Port 10103 (ezrelay)

IANA assigns port 10103 to ezrelay: eZrelay.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
ezrelay TCP eZrelay Albert C Yang -
ezrelay UDP eZrelay Albert C Yang -

Registry dates for this port: registered 2002-03.

Check what is listening on port 10103

Linux: is anything listening on TCP 10103?
sudo ss -tlnp 'sport = :10103'
Linux: UDP 10103
sudo ss -ulnp 'sport = :10103'
Linux / macOS: which process owns the port
sudo lsof -nP -i :10103
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':10103 '
Windows (Command Prompt)
netstat -ano | findstr :10103
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 10103 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 10103
From Windows
Test-NetConnection HOST -Port 10103
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 10103

Block port 10103 in the firewall

ufw
sudo ufw deny 10103/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 10103 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 10103 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 10103' -Direction Inbound -Protocol TCP -LocalPort 10103 -Action Block
ufw
sudo ufw deny 10103/udp
iptables
sudo iptables -A INPUT -p udp --dport 10103 -j DROP
nftables
sudo nft add rule inet filter input udp dport 10103 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 10103' -Direction Inbound -Protocol UDP -LocalPort 10103 -Action Block

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