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// Network services

Port 6699: Babel Routing Protocol over DTLS

Port 6699 is assigned by IANA to babel-dtls (Babel Routing Protocol over DTLS).

6699

How babel-dtls works

Network services
client:6699#%&@!x9response? client:6699#%&@!x9response?

The client sends a request to port 6699 and the babel-dtls service answers. Everything is encrypted: someone on the path only sees unreadable bytes.

Transport
UDP
Exposure risk
not rated depends on the program listening
Encryption
EncryptedTLS or built-in crypto
IANA status
Assigned1 registered service
Range
Registered (1024-49151)
Category
Network services
01 Security

Is port 6699 dangerous?

We have no specific security note for port 6699. 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 6699

ServicePortTransportDescriptionReferenceUpdated
babel-dtls 6699 UDP Babel Routing Protocol over DTLS RFC 8968 2020-09-04
-6699-Reserved--

// source: IANA service name and port number registry

03 Check it

Which program uses port 6699, and is it reachable?

Linux

sudo ss -ltnup 'sport = :6699'      # process listening on 6699
sudo lsof -nP -i :6699

macOS

sudo lsof -nP -i :6699

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 6699 -State Listen | Select LocalAddress, OwningProcess
Get-NetUDPEndpoint -LocalPort 6699
netstat -ano | findstr :6699

From another machine

nmap -p 6699 -sV <host>
sudo nmap -sU -p 6699 <host>
nc -zv <host> 6699

Block it in the firewall

sudo ufw deny 6699/udp                                         # Linux (ufw)
New-NetFirewallRule -DisplayName "Block 6699" -Direction Inbound -LocalPort 6699 -Protocol UDP -Action Block  # Windows
04 FAQ
What is port 6699 used for?

Port 6699 is assigned by IANA to babel-dtls (Babel Routing Protocol over DTLS).

Is port 6699 TCP or UDP?

Port 6699 is registered for UDP.

Is it safe to open port 6699?

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 6699 is open?

On Linux run "ss -ltnup 'sport = :6699'", on macOS "lsof -nP -i :6699", and on Windows "netstat -ano | findstr :6699" to see the local process. From another machine, "nmap -p 6699 <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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