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// Directory & authentication

Port 1813: RADIUS Accounting

Port 1813 is assigned by IANA to radius-acct (RADIUS Accounting).

1813

How radius-acct works

Directory & authentication
userdirectoryradius-acctresponse userdirectoryradius-acctresponse

The client proves who it is on port 1813 and gets an answer (or a ticket) it can use with other services.

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
Directory & authentication
01 Security

Is port 1813 dangerous?

We have no specific security note for port 1813. Its risk depends on the program actually listening on it. General advice for directory & authentication services:

  • Keep directory and authentication services on internal networks.
  • Require signing or TLS and disable anonymous queries.
  • Monitor authentication failures for spraying and brute force.
02 Registry

IANA registry entries for port 1813

ServicePortTransportDescriptionReferenceUpdated
radius-acct 1813 TCP, UDP RADIUS Accounting RFC 2866 -

// source: IANA service name and port number registry

03 Check it

Which program uses port 1813, and is it reachable?

Linux

sudo ss -ltnup 'sport = :1813'      # process listening on 1813
sudo lsof -nP -i :1813

macOS

sudo lsof -nP -i :1813

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 1813 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 1813
netstat -ano | findstr :1813

From another machine

nmap -p 1813 -sV <host>
sudo nmap -sU -p 1813 <host>
nc -zv <host> 1813

Block it in the firewall

sudo ufw deny 1813/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 1813" -Direction Inbound -LocalPort 1813 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 1813 used for?

Port 1813 is assigned by IANA to radius-acct (RADIUS Accounting).

Is port 1813 TCP or UDP?

Port 1813 is registered for TCP and UDP.

Is it safe to open port 1813?

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. Keep directory and authentication services on internal networks.

How do I check if port 1813 is open?

On Linux run "ss -ltnup 'sport = :1813'", on macOS "lsof -nP -i :1813", and on Windows "netstat -ano | findstr :1813" to see the local process. From another machine, "nmap -p 1813 <host>" shows whether it is reachable.

05 Related
:389 LDAP tcp · udp · high risk :636 LDAPS tcp · udp · moderate risk :88 Kerberos tcp · udp · high risk :3268 Global Catalog (LDAP) tcp · udp · high risk :1812 RADIUS udp · tcp · moderate risk :31 MSG Authentication tcp · udp :49 Login Host Protocol (TACACS) tcp · udp :56 XNS Authentication tcp · udp

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