Re: [RRG] some musings on PI v. PA, and assumptions, requirements, and tradeoffs

[Bruce Curtis <bruce.curtis@ndsu.edu>]

On Jul 16, 2007, at 3:44 AM, Brian E Carpenter wrote:

> On 2007-07-15 04:55, Bruce Curtis wrote:
> ...
> >   Another possibility to publish the the information is to put the  
> > multiple destination addresses in each packet.  Of course the cost  
> > is sending the extra bits. It seems to me that for devices in the  
> > core of the network the cost of publishing the info this way is  
> > mostly independent of the total number of routes or paths in the  
> > network but would instead be dependent on the number of  
> > destination addresses that would need to be supported per packet.
>
> It seems to me that Six/One (and to some extent shim6) is simply
> a compressed form of this - a packet contains enough info to
> recover the compressed into, which is the set of addresses. The only
> question is who's got a copy of the compression state.

  Yes, but for similar overhead (added bits) to encap/tunneling  
solutions we could put the info in the packet in uncompressed form.

> >   As you have pointed out before an architecture based on multiple  
> > destination addresses has it's own set of problems but it would  
> > allow for a future where TE could be done in the core while as you  
> > mention above the ability to do TE beyond the edge with other  
> > architectures can be quite expensive.
>
> You could do this neatly in IPv6 with a new form of routing header
> which simply lists alternate destination addresses.
>
>     Brian

  Right, something like

http://www.watersprings.org/pub/id/draft-bagnulo-multi6-mhexthdr-00.txt

  This could be implemented on hosts but would also allow middlebox  
solutions that strip or rewrite the header at the edge of the network  
so that between the edge of the network and the host there is only  
one destination address in the packet. (to make ACL management easier  
etc, also a possibility is to have one PI IP number per host that is  
not used for global routing but is one of the addresses in the  
headers plus the  PA addresses etc., another option is to have the PI  
addresses based on location/GPS etc)

  I think the property of easily supporting middlebox solutions but  
not requiring a middlebox (easily implemented on end hosts) is  
attractive.


---
Bruce Curtis                         bruce.curtis@ndsu.edu
Certified NetAnalyst II                701-231-8527
North Dakota State University


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