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Port 121 (erpc)

IANA assigns port 121 to erpc: Encore Expedited Remote Pro.Call.

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

IANA assignment

Service nameProtoDescriptionAssigneeReference
erpc TCP Encore Expedited Remote Pro.Call Jack ONeil -
erpc UDP Encore Expedited Remote Pro.Call Jack ONeil -

Check what is listening on port 121

Linux: is anything listening on TCP 121?
sudo ss -tlnp 'sport = :121'
Linux: UDP 121
sudo ss -ulnp 'sport = :121'
Linux / macOS: which process owns the port
sudo lsof -nP -i :121
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':121 '
Windows (Command Prompt)
netstat -ano | findstr :121
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 121 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 121
From Windows
Test-NetConnection HOST -Port 121
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 121

Block port 121 in the firewall

ufw
sudo ufw deny 121/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 121 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 121 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 121' -Direction Inbound -Protocol TCP -LocalPort 121 -Action Block
ufw
sudo ufw deny 121/udp
iptables
sudo iptables -A INPUT -p udp --dport 121 -j DROP
nftables
sudo nft add rule inet filter input udp dport 121 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 121' -Direction Inbound -Protocol UDP -LocalPort 121 -Action Block

Related ports

119NNTP120cfdptkt122smakynet123NTP

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