Subject: Re: site-local != NAT

From: Charlie Perkins <[email-masked]>
Date: Thu, 01 May 2003 01:44:03 -0700

Hello Tony,

Your example is very interesting:

Tony Hain wrote:

>>I have not heard any compelling operational requirement for 
>>ambiguous addresses in IPv6.
>>    
>>
>
>According to the definition above, anycast is one such case. Given that
>anycast is in daily operational use, there must be a requirement for
>addresses to refer to different physical devices in different parts of
>the network.
>  
>
For anycast, the application would be satisfied no matter which of the
several physical devices would respond.  Maybe we can say that
addresses should only be ambiguous when it is known by definition
that the ambiguity can never affect the applications using the address.

Regards,
Charlie P.

---

From: [email-masked]
Date: Thu, 01 May 2003 12:08:13 -0400

On Wed, 30 Apr 2003 15:55:00 PDT, Tony Hain said:

I'm confoozled here...  First you say:

> The point is they don't when they claim to be passing around 'opaque
> identifiers', at the same time they are explicitly assuming the content
> of that opaque object is a valid topology object at the receiver.

Right - and the entire problem with "site local" addresses is that they are
almost by definition ambiguous if they ever escape.  The host sending the
opaque blob has no a priori way of knowing if the blob will be in the *right*
scope when you get there.

I get tons of spam that have "http://192.168.1.10/...." URLs.  Whoops.

> addresses to refer to different physical devices in different parts of

Again, the biggest problem with using anycast is guaranteeing that all
references to "the same" object actually look identical - for instance,
all sorts of amusement can be obtained by running an anycast root DNS server
where the various instances advertise different serial numbers on the SOA
for '.'.

Ambiguous addresses are a Bad Idea.

---

From: Keith Moore <[email-masked]>
Date: Thu, 1 May 2003 16:54:57 -0400

> There is no inherent requirement that SL addresses be ambiguous, and
> there are several drafts out there on how to ensure they're not. 

for that matter, there's no inherent requirement that there be any 
set of addresses that is defined in the architecture to be filtered at
some arbitrary boundary.  in other words, there's no inherent
requirement for SLs at all.  

Keith

---

From: "Stephen Sprunk" <[email-masked]>
Date: Thu, 1 May 2003 15:48:28 -0500

[ Note to all:  can we please take all of these IPv6 threads off the main
IETF list?  Anyone interested can join the IPNG list ]

Thus spake <[email-masked]>
> Right - and the entire problem with "site local" addresses is that they
> are almost by definition ambiguous if they ever escape.  The host
> sending the opaque blob has no a priori way of knowing if the blob
> will be in the *right* scope when you get there.

So if what we call a "site local" address is always unique, even between
sites, that would pacify you?

There is no inherent requirement that SL addresses be ambiguous, and there
are several drafts out there on how to ensure they're not.  "Site local"
just means the address is only _reachable_ from its local site.

S

Stephen Sprunk         "God does not play dice."  --Albert Einstein
CCIE #3723         "God is an inveterate gambler, and He throws the
K5SSS        dice at every possible opportunity." --Stephen Hawking