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Port 5303 (hacl-probe)

IANA assigns port 5303 to hacl-probe: HA cluster probing.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
hacl-probe TCP HA cluster probing Eric Soderberg 2, Edward Yim -
hacl-probe UDP HA cluster probing Eric Soderberg 2, Edward Yim -

Check what is listening on port 5303

Linux: is anything listening on TCP 5303?
sudo ss -tlnp 'sport = :5303'
Linux: UDP 5303
sudo ss -ulnp 'sport = :5303'
Linux / macOS: which process owns the port
sudo lsof -nP -i :5303
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':5303 '
Windows (Command Prompt)
netstat -ano | findstr :5303
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 5303 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 5303
From Windows
Test-NetConnection HOST -Port 5303
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 5303

Block port 5303 in the firewall

ufw
sudo ufw deny 5303/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 5303 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 5303 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 5303' -Direction Inbound -Protocol TCP -LocalPort 5303 -Action Block
ufw
sudo ufw deny 5303/udp
iptables
sudo iptables -A INPUT -p udp --dport 5303 -j DROP
nftables
sudo nft add rule inet filter input udp dport 5303 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 5303' -Direction Inbound -Protocol UDP -LocalPort 5303 -Action Block

Related ports

5301hacl-gs5302hacl-cfg5304hacl-local5305hacl-test

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