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// Network services

Port 4126: Data Domain Replication Service

Port 4126 is assigned by IANA to ddrepl (Data Domain Replication Service).

4126

How ddrepl works

Network services
client:4126ddreplresponse client:4126ddreplresponse

The client sends a request to port 4126 and the ddrepl 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 4126 dangerous?

We have no specific security note for port 4126. 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 4126

ServicePortTransportDescriptionReferenceUpdated
ddrepl 4126 TCP, UDP Data Domain Replication Service - 2007-05

// source: IANA service name and port number registry

03 Check it

Which program uses port 4126, and is it reachable?

Linux

sudo ss -ltnup 'sport = :4126'      # process listening on 4126
sudo lsof -nP -i :4126

macOS

sudo lsof -nP -i :4126

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 4126 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 4126
netstat -ano | findstr :4126

From another machine

nmap -p 4126 -sV <host>
sudo nmap -sU -p 4126 <host>
nc -zv <host> 4126

Block it in the firewall

sudo ufw deny 4126/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 4126" -Direction Inbound -LocalPort 4126 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 4126 used for?

Port 4126 is assigned by IANA to ddrepl (Data Domain Replication Service).

Is port 4126 TCP or UDP?

Port 4126 is registered for TCP and UDP.

Is it safe to open port 4126?

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 4126 is open?

On Linux run "ss -ltnup 'sport = :4126'", on macOS "lsof -nP -i :4126", and on Windows "netstat -ano | findstr :4126" to see the local process. From another machine, "nmap -p 4126 <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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