On Apr 19, 2009, at 7:46 AM, Hui Deng wrote:
And you talked about Stuart Cheshire described a couple of IETFs ago,
Could you help to point out the link?
Sadly, I don't have it, but I suspect Stuart does, and I'm pretty sure
he's reading this.
The gist of what he was saying is that if you have an IPv4 address
that looks okay, and an IPv6 address that looks okay, you can't assume
that they *are* okay, because there may be no route to the global
internet on either your IPv4 or your IPv6 link. So you must attempt
to use both addresses, not just one, and you must do it at the same
time. Whichever one answers first, you take.
If you prefer either IPv4 or IPv6, and the transport you preferred
happens to be the one that was broken, a smart user will disable the
one you've preferred. That user will then advise his or her friends,
for example, that "IPv6 creates instability, so you should disable
it." This impedes deployment.
The unattended multiple interface situation is quite similar. I
think the attended case (a laptop with two or more network interfaces)
is actually better handled through user intervention, because the user
has knowledge of the physical situation that would be difficult to
communicate to the computer. But in the unattended case, you can get
into the same sort of "wrong learning" situation, where a smart but
naive user who debugs a network problem winds up learning a workaround
that would impede interoperability if everybody did it.
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