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// Network services

Port 1997: cisco Gateway Discovery Protocol

Port 1997 is assigned by IANA to gdp-port (cisco Gateway Discovery Protocol).

1997

How gdp-port works

Network services
client:1997gdp-portresponse client:1997gdp-portresponse

The client sends a request to port 1997 and the gdp-port service answers.

Transport
TCP · UDP
Exposure risk
not rated depends on the program listening
Encryption
Unknownnot stated by the registry
IANA status
Assigned1 registered service
Range
Registered (1024-49151)
Category
Network services
01 Security

Is port 1997 dangerous?

We have no specific security note for port 1997. Its risk depends on the program actually listening on it. General advice for network services services:

  • Answer only the networks that need the service (no open resolvers, relays or reflectors).
  • UDP services can be abused for DDoS amplification: rate-limit or block them at the edge.
  • Disable legacy test services that have no use in production.
02 Registry

IANA registry entries for port 1997

ServicePortTransportDescriptionReferenceUpdated
gdp-port 1997 TCP, UDP cisco Gateway Discovery Protocol - -

// source: IANA service name and port number registry

03 Check it

Which program uses port 1997, and is it reachable?

Linux

sudo ss -ltnup 'sport = :1997'      # process listening on 1997
sudo lsof -nP -i :1997

macOS

sudo lsof -nP -i :1997

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 1997 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 1997
netstat -ano | findstr :1997

From another machine

nmap -p 1997 -sV <host>
sudo nmap -sU -p 1997 <host>
nc -zv <host> 1997

Block it in the firewall

sudo ufw deny 1997/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 1997" -Direction Inbound -LocalPort 1997 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 1997 used for?

Port 1997 is assigned by IANA to gdp-port (cisco Gateway Discovery Protocol).

Is port 1997 TCP or UDP?

Port 1997 is registered for TCP and UDP.

Is it safe to open port 1997?

It depends on the program that listens on it. Open it only for a service you know and only to the networks that need it. Answer only the networks that need the service (no open resolvers, relays or reflectors).

How do I check if port 1997 is open?

On Linux run "ss -ltnup 'sport = :1997'", on macOS "lsof -nP -i :1997", and on Windows "netstat -ano | findstr :1997" to see the local process. From another machine, "nmap -p 1997 <host>" shows whether it is reachable.

05 Related
:53 DNS tcp · udp · moderate risk :135 MS RPC tcp · udp · high risk :123 NTP udp · tcp · moderate risk :67 DHCP server udp · tcp · moderate risk :111 rpcbind tcp · udp · high risk :9100 Raw printing (JetDirect) tcp · udp · high risk :631 IPP / CUPS tcp · udp · high risk :5353 mDNS udp · tcp · moderate risk

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