Port 1999 (tcp-id-port)

IANA assigns port 1999 to tcp-id-port: cisco identification port.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference

tcp-id-port TCP cisco identification port - -

tcp-id-port UDP cisco identification port - -

Linux: is anything listening on TCP 1999?

sudo ss -tlnp 'sport = :1999'

Linux: UDP 1999

sudo ss -ulnp 'sport = :1999'

Linux / macOS: which process owns the port

sudo lsof -nP -i :1999

Older Linux / BSD (net-tools)

sudo netstat -tlnp | grep ':1999 '

Windows (Command Prompt)

netstat -ano | findstr :1999

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 1999 -State Listen | Select LocalAddress,OwningProcess

From another machine

nc -vz -w 5 HOST 1999

From Windows

Test-NetConnection HOST -Port 1999

UDP probe (no reply does not prove it is closed)

nc -vzu -w 5 HOST 1999

ufw

sudo ufw deny 1999/tcp

iptables

sudo iptables -A INPUT -p tcp --dport 1999 -j DROP

nftables

sudo nft add rule inet filter input tcp dport 1999 drop

Windows Firewall

New-NetFirewallRule -DisplayName 'Block TCP 1999' -Direction Inbound -Protocol TCP -LocalPort 1999 -Action Block

ufw

sudo ufw deny 1999/udp

iptables

sudo iptables -A INPUT -p udp --dport 1999 -j DROP

nftables

sudo nft add rule inet filter input udp dport 1999 drop

Windows Firewall

New-NetFirewallRule -DisplayName 'Block UDP 1999' -Direction Inbound -Protocol UDP -LocalPort 1999 -Action Block

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