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Port 1997 (gdp-port)

IANA assigns port 1997 to gdp-port: cisco Gateway Discovery Protocol.

Registered (user) port, 1024-49151 TCPUDP

IANA assignment

Service nameProtoDescriptionAssigneeReference
gdp-port TCP cisco Gateway Discovery Protocol - -
gdp-port UDP cisco Gateway Discovery Protocol - -

Check what is listening on port 1997

Linux: is anything listening on TCP 1997?
sudo ss -tlnp 'sport = :1997'
Linux: UDP 1997
sudo ss -ulnp 'sport = :1997'
Linux / macOS: which process owns the port
sudo lsof -nP -i :1997
Older Linux / BSD (net-tools)
sudo netstat -tlnp | grep ':1997 '
Windows (Command Prompt)
netstat -ano | findstr :1997
Windows (PowerShell)
Get-NetTCPConnection -LocalPort 1997 -State Listen | Select LocalAddress,OwningProcess

Test it from outside

From another machine
nc -vz -w 5 HOST 1997
From Windows
Test-NetConnection HOST -Port 1997
UDP probe (no reply does not prove it is closed)
nc -vzu -w 5 HOST 1997

Block port 1997 in the firewall

ufw
sudo ufw deny 1997/tcp
iptables
sudo iptables -A INPUT -p tcp --dport 1997 -j DROP
nftables
sudo nft add rule inet filter input tcp dport 1997 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block TCP 1997' -Direction Inbound -Protocol TCP -LocalPort 1997 -Action Block
ufw
sudo ufw deny 1997/udp
iptables
sudo iptables -A INPUT -p udp --dport 1997 -j DROP
nftables
sudo nft add rule inet filter input udp dport 1997 drop
Windows Firewall
New-NetFirewallRule -DisplayName 'Block UDP 1997' -Direction Inbound -Protocol UDP -LocalPort 1997 -Action Block

Related ports

1995perf-port1996tr-rsrb-port1998x25-svc-port1999tcp-id-port

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