Phoenix won't respond on IPv4

I’m trying to setup a Vagrant box using generic/freebsd12 as the base image. I cannot get my Phoenix application to listen on IPv4 addresses inside the VM. It will respond to IPv6 as expected, so I know it works.

config :bison_app, BisonWeb.Endpoint,
  http: [
    port: String.to_integer(System.get_env("PORT") || "4000")
  url: [host: System.get_env("HOST") || "app.local"],
  cache_static_manifest: "priv/static/cache_manifest.json",
  secret_key_base: secret_key_base

From inside the VM:

$ curl -4 localhost:4000
curl: (7) Failed to connect to localhost port 4000: Connection refused

$ curl -6 localhost:4000
<HTML response>

I have the same problem on FreeBSD 13.2. Same code/configuration listens on IPv4 on Ubuntu.

Did you solve it somehow in the end?

Try adding the explicit IP to listen on? Not sure what the defaults are.


  config :my_app, MyWeb.Endpoint,
    url: [host: host, port: 443, scheme: "https"],
    http: [
      ip: {0, 0, 0, 0},
      port: port

Managed to solve it. I’m in the process of migrating from Ubuntu Linux to FreeBSD and for some reason on Ubuntu Linux Phoenix did bind to the IPv4, but using the same code and configuration on FreeBSD did bind only on IPv6.

I tried all tricks on changing config/config.exs, config/prod.exs and config/prod.secret.exs, but it turned out that the problem was in the lib/my_app_web/endpoint.ex where in init function had the following line:

{:ok, Keyword.put(config, :http, [:inet6, port: port])}

Changing it to:

{:ok, Keyword.put(config, :http, [:inet, port: port])}

I’m pretty sure that this line has been on inet6 for the entire time of the project and it was generated by at the time of project creation. Just bear in mind that this is a legacy Phoenix application running version 1.5.1 and might not have the same generated file when creating a new Phoenix application today.


On Linux, by default, an “inet6” socket also accepts IPv4 (you can disable that with the sysctl option net.ipv6.bindv6only or by adding {ipv6_v6only: true} to your socket options). On FreeBSD, it is not the case by default. You can enable a similar behaviour by adding ipv6_ipv4mapping=YES in /etc/rc.conf. See rc.conf(5)

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