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// Other services

Port 1977: TCO Address Book

Port 1977 is assigned by IANA to tcoaddressbook (TCO Address Book).

1977

How tcoaddressbook works

Other services
client:1977tcoaddressbookresponse client:1977tcoaddressbookresponse

The client sends a request to port 1977 and the tcoaddressbook 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
Other services
01 Security

Is port 1977 dangerous?

We have no specific security note for port 1977. Its risk depends on the program actually listening on it. General advice for other services services:

  • Close the port if nothing on the host needs it.
  • Identify the process that listens on it (commands below) before opening it in a firewall.
  • Expose a service only to the networks that use it.
02 Registry

IANA registry entries for port 1977

ServicePortTransportDescriptionReferenceUpdated
tcoaddressbook 1977 TCP, UDP TCO Address Book - -

// source: IANA service name and port number registry

03 Check it

Which program uses port 1977, and is it reachable?

Linux

sudo ss -ltnup 'sport = :1977'      # process listening on 1977
sudo lsof -nP -i :1977

macOS

sudo lsof -nP -i :1977

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 1977 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 1977
netstat -ano | findstr :1977

From another machine

nmap -p 1977 -sV <host>
sudo nmap -sU -p 1977 <host>
nc -zv <host> 1977

Block it in the firewall

sudo ufw deny 1977/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 1977" -Direction Inbound -LocalPort 1977 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 1977 used for?

Port 1977 is assigned by IANA to tcoaddressbook (TCO Address Book).

Is port 1977 TCP or UDP?

Port 1977 is registered for TCP and UDP.

Is it safe to open port 1977?

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. Close the port if nothing on the host needs it.

How do I check if port 1977 is open?

On Linux run "ss -ltnup 'sport = :1977'", on macOS "lsof -nP -i :1977", and on Windows "netstat -ano | findstr :1977" to see the local process. From another machine, "nmap -p 1977 <host>" shows whether it is reachable.

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