Re: IPv6 socket behaviour different to IPv4?

[Roy Marples <roy%marples.name@localhost>]

On 04/06/2014 12:30, Darren Reed wrote:
> > > > > But when I configure "fd00::1" or "1::1" as an IPv6 address, I 
> > > > > would
> > > > > expect that the system should be able to recognise that there is no
> > > > > desire on my part to change the address should a conflict arise but
> > > > > I can't see any way for the kernel to divine that when it is just 
> > > > > given
> > > > > an IP address.
> > > >
> > > > Why do you have this desire?
> > > > If any address is on-link, DAD needs to be performed.
> > >
> > > Put yourself in an IPv6 only world...
> >
> > Not relevant to the discussion, the same logic also applies to IPv4 
> > although this requires a good userland daemon like say dhcpcd.
>
> In an IPv4 world, if I put "10.1.1.1 netbsd" in my hosts file and
> manually assign 10.1.1.1 to any network interface, then I will
> always be able to connect to 10.1.1.1 and thus "netbsd".

I said a good userland daemon, not manual assignment :)


> > > In your /etc/hosts file, you have an entry in it for an IPv6 address
> > > to be assigned to your hostname and no other line with your hostname.
> > >
> > > As soon as you disconnect from the network, you can no longer do
> > > "ssh hostname".
> >
> > And this is a problem how exactly? `ssh localhost` still works.
> > Sounds more like a local name resolution issue than an address 
> > availability one.
>
> Rinse and repeat by replacing "hostname" with a static IP address that
> you have assigned to a network interface.

I'm still not entirely sure what your use case is or why you believe 
it's important to talk to an address on a non functioning interface (ie, 
it's down or no carrier)
If you want the same behavioral traits as IPv4 then at a guess you would 
need to make IN6_IFF_NODAD assignable from userland (currently it's 
rejected).
I'm not entirely sure that's a good idea though.

Roy