Re: Move forward

[Iljitsch van Beijnum <iljitsch@muada.com>]

On 17 Mar 2003, marcelo bagnulo wrote:

> > > However in IPv6, considering "Default
> > > Address Selection mechanism" i was hoping that application used the list
> > > of addresses generated by the mechanism and try to use them to
> > > communicate

> > Actually this may make it worse, as the "best" address is always
> > selected. If the "best" address is unreachable, no dice. At least with
> > random or round robin you can hit reload to try again.

> From RFC 3484

> 6. Destination Address Selection

>    The destination address selection algorithm takes a list of
>    destination addresses and sorts the addresses to produce a new list.
>                                                                   ^^^^
> I guess that applications now obtain a list of addresses, after the
> default address selection mechanism has sorted them.

Yes. But then the application still has to go through the trouble of
trying every address. I don't think web browsers typically do that. (And
if the user has to wait for a timeout, it might not matter anyway.)

For your experimentation pleasure I have created some DNS names with 7
IPv4 and/or IPv6 addresses, only one of which works. It's a Cisco, so
you can telnet, but HTTP is probably more interesting (if it works,
you'll get an authentication requester). The names are:

tryme.bgpexpert.com trymev4.bgpexpert.com trymev6.bgpexpert.com

> Moreover, the first rule of the mechanism discards unreachable
> destinations, so if one of multiple is unreachable it will be included
> last.

How does the resolver library know which addresses are reachable? Or
usable for the application in question?