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// Other services

Port 1611: Inter Library Loan

Port 1611 is assigned by IANA to ill (Inter Library Loan).

1611

How ill works

Other services
client:1611illresponse client:1611illresponse

The client sends a request to port 1611 and the ill 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 1611 dangerous?

We have no specific security note for port 1611. 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 1611

ServicePortTransportDescriptionReferenceUpdated
ill 1611 TCP, UDP Inter Library Loan - -

// source: IANA service name and port number registry

03 Check it

Which program uses port 1611, and is it reachable?

Linux

sudo ss -ltnup 'sport = :1611'      # process listening on 1611
sudo lsof -nP -i :1611

macOS

sudo lsof -nP -i :1611

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 1611 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 1611
netstat -ano | findstr :1611

From another machine

nmap -p 1611 -sV <host>
sudo nmap -sU -p 1611 <host>
nc -zv <host> 1611

Block it in the firewall

sudo ufw deny 1611/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 1611" -Direction Inbound -LocalPort 1611 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 1611 used for?

Port 1611 is assigned by IANA to ill (Inter Library Loan).

Is port 1611 TCP or UDP?

Port 1611 is registered for TCP and UDP.

Is it safe to open port 1611?

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 1611 is open?

On Linux run "ss -ltnup 'sport = :1611'", on macOS "lsof -nP -i :1611", and on Windows "netstat -ano | findstr :1611" to see the local process. From another machine, "nmap -p 1611 <host>" shows whether it is reachable.

05 Related
:4444 Metasploit default / krb524 tcp · udp · high risk :31337 Back Orifice / elite tcp · udp · high risk :1 TCP Port Service Multiplexer tcp · udp :5 Remote Job Entry tcp · udp :9 Discard tcp · udp · sctp · dccp :11 Active Users tcp · udp :17 Quote of the Day tcp · udp :18 Message Send Protocol (historic) tcp · udp

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