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Port 596 (smsd)

IANA assigns port 596 to smsd: SMSD.

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

IANA assignment

Service nameProtoDescriptionAssigneeReference
smsd TCP SMSD Wayne Barlow -
smsd UDP SMSD Wayne Barlow -

Check what is listening on port 596

Linux: is anything listening on TCP 596?
sudo ss -tlnp 'sport = :596'
Linux: UDP 596
sudo ss -ulnp 'sport = :596'
Linux / macOS: which process owns the port
sudo lsof -nP -i :596
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':596 '
Windows (Command Prompt)
netstat -ano | findstr :596
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 596 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 596
From Windows
Test-NetConnection HOST -Port 596
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 596

Block port 596 in the firewall

ufw
sudo ufw deny 596/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 596 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 596 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 596' -Direction Inbound -Protocol TCP -LocalPort 596 -Action Block
ufw
sudo ufw deny 596/udp
iptables
sudo iptables -A INPUT -p udp --dport 596 -j DROP
nftables
sudo nft add rule inet filter input udp dport 596 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 596' -Direction Inbound -Protocol UDP -LocalPort 596 -Action Block

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Assignment data: IANA port number registry (public domain), retrieved 2026-11-10.