Re: (web server) serving on both ipv6 and ipv4?

[Chris Vine]

On Wed, 19 Jan 2022 08:57:51 +0100
"Dr. Arne Babenhauserheide" <arne_bab@web.de> wrote:
> Hi,
> 
> 
> with both fibers server and (web server) there is a split between IPv4
> and IPv6:
> 
> IPv4:
> 
>     (fibers:run-server handler-with-path #:family AF_INET #:port port #:addr 
> INADDR_ANY)
> 
>     (run-server handler-with-path 'http `(#:host "localhost" #:family 
> ,AF_INET #:addr ,INADDR_ANY #:port ,port))
> 
> IPv6:
> 
>     (define s
>         (let ((s (socket AF_INET6 SOCK_STREAM 0)))
>             (setsockopt s SOL_SOCKET SO_REUSEADDR 1)
>             (bind s AF_INET6 (inet-pton AF_INET6 ip) port)
>             s))
>     (fibers:run-server handler-with-path #:family AF_INET6 #:port port #:addr 
> (inet-pton AF_INET6 ip) #:socket s)
> 
>     (define s
>         (let ((s (socket AF_INET6 SOCK_STREAM 0)))
>             (setsockopt s SOL_SOCKET SO_REUSEADDR 1)
>             (bind s AF_INET6 (inet-pton AF_INET6 ip) port)
>             s))
>     (run-server handler-with-path 'http `(#:family ,AF_INET6 #:addr 
> (inet-pton AF_INET6 ip) #:port ,port #:socket ,s))
> 
> 
> Is there a way to bind to both IPv6 and IPv4, so my server will react to
> requests regardless of whether a client reaches my computer over IPv4 or
> IPv6?

As I understand it, with linux IPv6 sockets are dual stack capable, and
in earlier kernel versions this was be enabled by default.  I believe
with current versions that is no longer the case, and that you have to
specifically enable dual stack by turning off IPV6_V6ONLY using
setsockopt before binding on the socket.

Then, if receiving a IPv4 connection from address 1.2.3.4, this would be
mapped as ::::ffff:1.2.3.4.

I do not know about other OSes.  I have half a memory that some earlier
versions of windows did not support dual stack sockets (XP?).