CyberHunter
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// Network services

Port 647: DHCP Failover

Port 647 is assigned by IANA to dhcp-failover (DHCP Failover).

647

How dhcp-failover works

Network services
client:647dhcp-failoverresponse client:647dhcp-failoverresponse

The client sends a request to port 647 and the dhcp-failover 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
Well-known (0-1023)
Category
Network services
01 Security

Is port 647 dangerous?

We have no specific security note for port 647. 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 647

ServicePortTransportDescriptionReferenceUpdated
dhcp-failover 647 TCP, UDP DHCP Failover RFC 8156 2018-05-21

// source: IANA service name and port number registry

03 Check it

Which program uses port 647, and is it reachable?

Linux

sudo ss -ltnup 'sport = :647'      # process listening on 647
sudo lsof -nP -i :647

macOS

sudo lsof -nP -i :647

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 647 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 647
netstat -ano | findstr :647

From another machine

nmap -p 647 -sV <host>
sudo nmap -sU -p 647 <host>
nc -zv <host> 647

Block it in the firewall

sudo ufw deny 647/tcp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 647" -Direction Inbound -LocalPort 647 -Protocol TCP -Action Block  # Windows
04 FAQ
What is port 647 used for?

Port 647 is assigned by IANA to dhcp-failover (DHCP Failover).

Is port 647 TCP or UDP?

Port 647 is registered for TCP and UDP.

Is it safe to open port 647?

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 647 is open?

On Linux run "ss -ltnup 'sport = :647'", on macOS "lsof -nP -i :647", and on Windows "netstat -ano | findstr :647" to see the local process. From another machine, "nmap -p 647 <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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