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Port 3550 (ssmpp)

IANA assigns port 3550 to ssmpp: Secure SMPP.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
ssmpp TCP Secure SMPP Cormac Long -
ssmpp UDP Secure SMPP Cormac Long -

Registry dates for this port: registered 2002-07.

Check what is listening on port 3550

Linux: is anything listening on TCP 3550?
sudo ss -tlnp 'sport = :3550'
Linux: UDP 3550
sudo ss -ulnp 'sport = :3550'
Linux / macOS: which process owns the port
sudo lsof -nP -i :3550
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':3550 '
Windows (Command Prompt)
netstat -ano | findstr :3550
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 3550 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 3550
From Windows
Test-NetConnection HOST -Port 3550
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 3550

Block port 3550 in the firewall

ufw
sudo ufw deny 3550/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 3550 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 3550 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 3550' -Direction Inbound -Protocol TCP -LocalPort 3550 -Action Block
ufw
sudo ufw deny 3550/udp
iptables
sudo iptables -A INPUT -p udp --dport 3550 -j DROP
nftables
sudo nft add rule inet filter input udp dport 3550 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 3550' -Direction Inbound -Protocol UDP -LocalPort 3550 -Action Block

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