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Port 992 (Telnet over TLS)

Telnet over TLS, mostly seen on IBM i (AS/400) 5250 terminal access.

Well-known (system) port, 0-1023 TCP Remote access Expose only to trusted sources

What port 992 is used for

Telnet over TLS, mostly seen on IBM i (AS/400) 5250 terminal access.

Security: should port 992 be open?

Expose only to trusted sources. Prefer SSH where possible.

IANA assignment

Service nameProtoDescriptionAssigneeReference
telnets TCP telnet protocol over TLS/SSL - -
telnets UDP telnet protocol over TLS/SSL - -

Check what is listening on port 992

Linux: is anything listening on TCP 992?
sudo ss -tlnp 'sport = :992'
Linux / macOS: which process owns the port
sudo lsof -nP -i :992
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':992 '
Windows (Command Prompt)
netstat -ano | findstr :992
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 992 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 992
From Windows
Test-NetConnection HOST -Port 992

Allow only trusted sources on port 992 in the firewall

Replace 203.0.113.10 with the address or network you trust. With ufw, make sure the default incoming policy is deny.

ufw (one trusted source)
sudo ufw allow from 203.0.113.10 to any port 992 proto tcp
iptables
sudo iptables -A INPUT -p tcp --dport 992 -s 203.0.113.10 -j ACCEPT
sudo iptables -A INPUT -p tcp --dport 992 -j DROP
nftables
sudo nft add rule inet filter input ip saddr 203.0.113.10 tcp dport 992 accept
sudo nft add rule inet filter input tcp dport 992 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'TCP 992 trusted' -Direction Inbound -Protocol TCP -LocalPort 992 -RemoteAddress 203.0.113.10 -Action Allow

Related ports

23Telnet22SSH990FTPS (implicit, control)991nas993IMAPS995POP3S

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