I'm going to answer this in a general, architectural approach level,
and not specific to particular issues.
At 16:21 +0200 6/16/10, <[email protected]> wrote:
So from your point of view, it would be best for a host to contact
DNS server's
of all interfaces, and then use source/destination address selection to choose
from the resulting list what address to actually use?
Not necessarily. What I mean is that it is up to the multi-homed
device to decide what interfaces are candidates (for the pending data
transmission) and consult the DNS on each interface. However, what
one interface says is not necessarily valid for another, for example,
if the address (I'll use v4 now just because it's quicker to type,
however I know you are in the v6 mode) for a SMTP server is 127.1.2.3
on wireless and 127.3.2.1 on wired, you can't then use 127.3.2.1 on
the wireless. No mixing and matching of the results.
Meaning you don't see this problematic:
Yes, those are issues - for the multi-homed device.
The question (I believe) is whether split DNS is a problem for
multihomed devices. Yes, I think it is. But that doesn't mean split
DNS is the culprit. Does that mean multi-homed devices are the
problem then? No. Both split DNS and multi-homing are fine.
However, there is a need for multi-homed devices to know how to deal
with split DNS. (And not vice versa.)
Why not vice versa? My argument here isn't that coherent because I
haven't spend enough time thinking it over. Generally, multi-homing
is a special case and the DNS serves a wide population that is mostly
signal-homed. Yes, today my laptop qualifies as multihomed (the RJ-45
port and the wireless card are active and at times I have a cable
plugged in). Still, the host behaves as single-homed (maybe the
wireless hasn't found a SSID it can use).
In the future, as a device is multi-homed, it needs to deal with that
fact locally. It might decide not to use the 802.11 radio but use
the GSM radio, or neither and use the Bluetooth. But that choice
will be made before worrying about what DNS server. By the time it
chooses what DNS server to use, the interface is picked.
An enlightened host might be very agile on the interface choice - as
the 802.11 fades out the GSM is used with sessions flipping over to
the new transport (that results from the new data link). Again in
this case, the flipping is done and then the DNS server is changed.
I guess I am saying, to a multi-homed device, what DNS server to use
is the tail of the "what i/f to use" dog.
[http://www.urbandictionary.com/define.php?term=the%20tail%20wagging%20the%20dog&defid=3285170]
Apologies if this isn't that clear.
--
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Edward Lewis
NeuStar You can leave a voice message at +1-571-434-5468
Discussing IPv4 address policy is like deciding what to eat on the Titanic.
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