Re: Troubles with adding IPv6 support to a program

From: Chris Ross <>
Date: Sun, 12 Jun 2022 17:19:35 UTC
Okay.  So, anyone can feel free to look at my code at the link below, but 
as soon as I got desperate enough to reach out to a mailer, I found my
own mistake.

For the curious, inside my loop I was calling socket() with the original
pointer, not the iterator.  :-(   So, calling socket() the same way
twice despite thinking I wasn’t.

Sorry for the noise.

                        - Chris

> On Jun 12, 2022, at 12:40, Chris Ross <> wrote:
> Tl;dr;
> I don’t know why I’m getting an EINVAL from a call to bind for a second socket
> 20 years ago, I spent a lot of time adding IPv6 support to IPv4-only programs.
> So I thought this (adding IPv6 support to simpleproxy[1]) would be an easy
> project to pick up.  I’ve gotten most of the framework in, delayed only
> slightly when I learned that FreeBSD is “different” in not routing IPv4
> traffic to AF_INET6 sockets [2].
> However, I’m getting an issue from one of my bind(2) calls that I’m not able
> to figure out.  I was hoping someone else had a few minutes to take a quick
> look and help me find out what I’m doing wrong.
> A ~70 line relevant section of the source is at
> The tl;dr; of this is that I:
> * getaddrinfo(NULL, portIwant)
> * for each address returned:
> * create a socket
> * setsockopt(SO_REUSEADDR)
> * bind
> * listen
> The first address I get is IPv6 localhost, and that binds and listens, then
> continues to the next address.  A new socket is created, setsockopt’d, but
> bind for the second address (IPv4 localhost) fails with EINVAL.
> As you can see in the code shared, I have lots of debugging logs in the code,
> and it looks like everything is as it should be.  I’m probably just missing
> Something simple, and am looking for another set of eyes.
> Thanks all.  Contact me off list if you like, or on-list if it’s obvious
> what I’ve done and it will help others.
>              - Chris
> [1]
> [2] inet6(4), "Interaction between IPv4/v6 sockets"