I have an application that listen on udp port 1234. I already added the udp/1234 in my firewall and checked if the port is already added to the allowed ports. When I checked if the port is listening using netstat, the port is using udp6 instead of udp. Is there a way to change this to udp instead of udp6. please see image for reference. My Application is running in CentOS 7.


This is not a problem. Try sending UDP to this service.

AF_INET6 address family also works for IPv4. With both the Linux network stack, and the presumably Java application given the process name you have listening.

  • Thanks for the answer. Now it is clear to me how this things work. I already tested my connection using nc and it worked. – lazy Apr 6 '19 at 4:39
  • This API compatibility seems unusual if you just know IPv6 is a separate protocol. But it is by design if you look at RFC 2553 and man 7 ipv6 – John Mahowald Apr 6 '19 at 10:59

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