Re: [RRG] Separation vs. Elimination

[Michael Meisel <meisel@cs.ucla.edu>]

Hi Steve,

Steven Blake wrote:
> 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.

Fair enough. I think this is really just a semantics issue though, the
point is, whatever namespace you use to identify the hosts in your local
network, those names are independent of the names that get used for
global routing, and they are independent from who your provider(s)
is/are. This is consistent with our definition of separation. Perhaps we
should call it "PI namespace" or "local namespace" or something.

>>> |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).

True, there are no edge site prefixes in GSE, so this wording doesn't
quite match up. But DNS does associates the destination *portion of the
address* with the corresponding transit *portion of the address*. That
is, an "RG Name" lookup looks like a mapping lookup to me, it just
happens at the host instead of the border router.

-Michael

> Regards,
> 
> // Steve
> 
> 
> 
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