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Port 4591 (l3t-at-an)

IANA assigns port 4591 to l3t-at-an: HRPD L3T (AT-AN).

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
l3t-at-an TCP HRPD L3T (AT-AN) Avi Lior -
l3t-at-an UDP HRPD L3T (AT-AN) Avi Lior -

Registry dates for this port: registered 2009-02-27.

Check what is listening on port 4591

Linux: is anything listening on TCP 4591?
sudo ss -tlnp 'sport = :4591'
Linux: UDP 4591
sudo ss -ulnp 'sport = :4591'
Linux / macOS: which process owns the port
sudo lsof -nP -i :4591
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':4591 '
Windows (Command Prompt)
netstat -ano | findstr :4591
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 4591 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 4591
From Windows
Test-NetConnection HOST -Port 4591
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 4591

Block port 4591 in the firewall

ufw
sudo ufw deny 4591/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 4591 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 4591 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 4591' -Direction Inbound -Protocol TCP -LocalPort 4591 -Action Block
ufw
sudo ufw deny 4591/udp
iptables
sudo iptables -A INPUT -p udp --dport 4591 -j DROP
nftables
sudo nft add rule inet filter input udp dport 4591 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 4591' -Direction Inbound -Protocol UDP -LocalPort 4591 -Action Block

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4573cardifftec-back4590rid4592hrpd-ith-at-an4593ipt-anri-anri

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