Re: [RRG] Separation vs. Elimination

[Steven Blake <slblake@petri-meat.com>]

On Tue, 23 Sep 2008 13:03:04 -0700, Michael Meisel <meisel@cs.ucla.edu>
wrote:

> Hi Tony,
> 
> Tony Li wrote:
>>
>>
>> |So it seems to me that ESDs are similar to PI addresses (i.e.  GSE
>> |doesn't eliminate the USE of PI addresses, but does get rid of them
>> |in the transit space).
>>
>>
>> This is exactly where I have to disagree.  The ESD is simply not an
>> address. It is a wholly orthogonal namespace.  While it is globally
unique, it
>> shares no other properties with a PI address that I can see.
> 
> But it must be used as an address in edge networks, right? How else
> would a packet get routed to its final destination host once it gets to
> the destination network?

By STP + ESD (last 80 bits of the address field).  ESD is just an interface

identifier, no different than the IID in IPv6.  It's only really used in
the
neighbor table lookup on the last hop router.

Please re-read
http://ietfreport.isoc.org/all-ids/draft-ietf-ipngwg-gseaddr-00.txt.

> When Lan says "PI address", she's referring in a general sense to an
> address that wasn't assigned by your provider. It could certainly come
> from a different namespace than PA addresses under a separation scheme,
> since the PI addresses are no longer used in core routing. So in this
> sense, I would call the ESD a "PI address".

ESD bits are never used in a routing lookup, so I don't know why you want
to call
it an address by itself.

>> |How is GSE similar to NAT?
>>
>>
>> GSE does pure translation on the routing bits.  In a NAT environment,
                                   ^backbone

>> the routing goop is translated into an RFC 1918 address.  In GSE, the
>> routing goop gets zeroed out.
>>
>> GSE is better than NAT in that it does provide a real identifier that
>> applications can now exchange freely, so that much of the translation
>> ugliness within NAT (e.g., FTP port commands) can go away.
> 
> It seems to me that there is still an important fundamental difference:
> when you address a packet to a host behind a NAT, you are addressing the
> packet to the routing goop directly. The translation happens only
> locally on the destination end (and ugliness results).

That's true of IPv4 NAT, but in (hypothetical) IPv6 NAT you would never
want
to translate anything other than the provider prefix. 

> With GSE, on the other hand, if you address a packet to a host inside a
> GSE network, you are addressing the packet to the ESD, so you need
> mapping information (from DNS, in this case) to determine the correct
> routing goop.

That's true of IPv6 in general, whether the edge site is using PA or PI 
prefixes internally (or would have been, if A6 records had survived).

As I pointed out previously, there is no concept of globally unique edge
site 
prefixes in GSE.  There is no destination prefix translation anywhere
upstream
of the destination edge site's border router.  Ergo, there is no mapping
system
that "associate(s) an edge prefix with the corresponding transit address". 
The
routing behavior in GSE is unchanged from IPv6 outside of the destination
edge site
(excepting the source prefix re-write).


Regards,

// Steve



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