Subj : Feature request: soft IPv6 force
To   : All
From : Andrei Dzedolik
Date : Tue Apr 24 2018 04:13 pm

Greetings, travelers ...

20 Apr 18 21:59, Michiel van der Vlist wrote to me:

 AD>> So, is this statement correct:
 AD>> 1. Introduce new configuration option for FTN node object to
 AD>> force IPv6 or IPv4 precedence, disrespecting the OS rules for
 AD>> this node only;

 MV> Yep, that is the heart of my feature request.

I may need your help here. Again.
I have identified the place and way to implement this request: most feasible 
and elegant from my point of view will be to perform an 'addrinfo' structures 
list reordering before passing it forward. This could be done in very 
controlled manner and whole feature this wasy will be activted by compile time 
option.

Now to the tricky part :)
One can imagine addrinfo structure list as a list of pre-ordered IP addresses. 
The 'getaddrinfo' doing this as we know depending on gai.conf settings on 
somehting similair. In the simpliest case, with standard IPv6 over IPv4 
precedence we'll end up with the list of:

IPv6 #1 -> ... -> IPv6 #N -> IPv4 #1 -> ... -> IPv4 #N -> NULL

Quick and dirty way to reorder it is to find IPv4 #1 and put into the head, 
then find last IPv4 #N and put it's pointer to the IPv6 #1 and finally IPv6 #N 
to -> NULL.
But ... (remember Ned Stark) ... there is possibiliy, as far as I can read from 
RFC, the list will be mix of v4 and v6 addresses. So we'll have:

IPv6 #1 -> IPv6 #N -> IPv4 #1 ... -> IPv4 #N -> IPv6 #N+1 -> ... -> IPv6 #N+M 
-> NULL

This is possible so far in case IPv4 over IPv6 tunneling has lower precedence, 
than IPv4, but pure IPv6 is still prefered.

Bearing your idea in mind, how should requested feature deal with such lists?

p.s. To do not induct your way of thinking I would no post my solution. At 
least not now :)

Cheers,

\aID


--- GoldED+/BSD 1.1.5-b20170303
 * Origin: Hugayda Station (2:463/1331)

.