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// File transfer & sharing

Port 21213: Cohesity backup agents

Port 21213 is assigned by IANA to cohesity-agent (Cohesity backup agents).

21213

How cohesity-agent works

File transfer & sharing
client:212131/32/33/3cohesity-agent client:212131/32/33/3cohesity-agent

Files are sent over port 21213 in pieces and reassembled on the other side.

Transport
TCP
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
File transfer & sharing
01 Security

Is port 21213 dangerous?

We have no specific security note for port 21213. Its risk depends on the program actually listening on it. General advice for file transfer & sharing services:

  • Prefer encrypted protocols (SFTP, FTPS, SMB 3 with encryption).
  • Disable anonymous access and restrict shares or exports to known hosts.
  • Never publish file sharing protocols to the Internet.
02 Registry

IANA registry entries for port 21213

ServicePortTransportDescriptionReferenceUpdated
cohesity-agent 21213 TCP Cohesity backup agents - 2019-08-01
-21213-Reserved--

// source: IANA service name and port number registry

03 Check it

Which program uses port 21213, and is it reachable?

Linux

sudo ss -ltnup 'sport = :21213'      # process listening on 21213
sudo lsof -nP -i :21213

macOS

sudo lsof -nP -i :21213

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 21213 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 21213
netstat -ano | findstr :21213

From another machine

nmap -p 21213 -sV <host>
nc -zv <host> 21213

Block it in the firewall

sudo ufw deny 21213/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 21213" -Direction Inbound -LocalPort 21213 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 21213 used for?

Port 21213 is assigned by IANA to cohesity-agent (Cohesity backup agents).

Is port 21213 TCP or UDP?

Port 21213 is registered for TCP.

Is it safe to open port 21213?

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. Prefer encrypted protocols (SFTP, FTPS, SMB 3 with encryption).

How do I check if port 21213 is open?

On Linux run "ss -ltnup 'sport = :21213'", on macOS "lsof -nP -i :21213", and on Windows "netstat -ano | findstr :21213" to see the local process. From another machine, "nmap -p 21213 <host>" shows whether it is reachable.

05 Related
:445 SMB tcp · udp · critical risk :21 FTP tcp · udp · sctp · high risk :139 NetBIOS Session tcp · udp · high risk :69 TFTP udp · tcp · high risk :2049 NFS tcp · udp · sctp · high risk :873 rsync tcp · udp · high risk :20 File Transfer [Default Data] tcp · udp · sctp :115 Simple File Transfer Protocol tcp · udp

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