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Port 1121 (rmpp)

IANA assigns port 1121 to rmpp: Datalode RMPP.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
rmpp TCP Datalode RMPP Dave Ruedger -
rmpp UDP Datalode RMPP Dave Ruedger -

Registry dates for this port: registered 2003-11.

Check what is listening on port 1121

Linux: is anything listening on TCP 1121?
sudo ss -tlnp 'sport = :1121'
Linux: UDP 1121
sudo ss -ulnp 'sport = :1121'
Linux / macOS: which process owns the port
sudo lsof -nP -i :1121
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':1121 '
Windows (Command Prompt)
netstat -ano | findstr :1121
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 1121 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 1121
From Windows
Test-NetConnection HOST -Port 1121
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 1121

Block port 1121 in the firewall

ufw
sudo ufw deny 1121/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 1121 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 1121 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 1121' -Direction Inbound -Protocol TCP -LocalPort 1121 -Action Block
ufw
sudo ufw deny 1121/udp
iptables
sudo iptables -A INPUT -p udp --dport 1121 -j DROP
nftables
sudo nft add rule inet filter input udp dport 1121 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 1121' -Direction Inbound -Protocol UDP -LocalPort 1121 -Action Block

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