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Re: [RRG] SHIM6: portability, ULAs, mobility etc.


El 02/08/2007, a las 22:14, Robin Whittle escribió:


Thanks Marcelo for helping me understand SHIM6, in the thread "On
the Transitionability of LISP":


             SHIM6  Six/  Mobile  LISP-   LISP-   eFIT-  Ivip
                    One   IPv6    NERD    CONS    APT

Address
portability                       Y       Y       Y      Y

Multihoming   Y     Y             Y       Y       Y      Y

Mobility                  Y                              Y*

IPv4 too                          Y       Y       Y      Y

No host                           Y       Y       Y      Y*
changes


Just to point out that:

Shim6 can support address portability, if you use portable
identifiers, such as ULAs. No need to change anything in the shim6
specs to support that.


My understanding of Shim6 is not ideal, but I don't know how this
could work.  How could host A send a packet to host B in the first
place if host B had a ULA address?
i assume that hosts will have (routable) locators bsides the ULAs that will used as ULIDs.
So, the communication will flow using ULAs as ULIDs and PA addresses as locators. Assuming that all applications use identifiers, you can renumber the locators without impact or need for manual reconfiguration. 




Shim6 can be used as a RO mechanism for mobility, (it does not
provides mobility anchor point capabilities, though)


I assume "RO" means Router Only.


No, RO means route optimization


I can't imagine exactly how this
would work.  Can you give an example?
this is long. but it is described in detail in http:// www.watersprings.org/pub/id/draft-bagnulo-shim6-mip-00.txt 





Shim6 can easily support v4 locators (but not v4 identifiers) (the
NAT traversal capabilities would need to be worked out, but we are
discussing about that)
Shim6 is therefore not of any help for IPv4 hosts trying to communicate. 



shim6 requires host to be updated to benefit from it.
So shim6 can be used in v4 sites (i.e. sites wihtout v6 connectivity), but the hosts will need v6 addresses to be used as locators. Please note that it is perfctly possible that the hosts involved have no v6 locators. 




I don't know what kind of problem being solved is "No host
changed" though... why didn't you include a line about "No router
changes"? ;-)


I agree that no router changes is a definite benefit of SHIM6.
Likewise, along with Six/One, the lack of tunneling and the increase
in packet overhead, MTU and fragmentation limits etc. is a major
advantage over LISP/eFIT-APT/Ivip etc.

However, I am thinking about 99.9% of today's Internet users over
the next five to ten years.



not sure what do you mean about this....




However, the main limitation of shim6 is about traffic
engineering, that you seem to have missed. Shim6 do provides host
enforced TE capabilities, but does not provides router enforced TE
capabilitis, which seems to be a desired feature. (OTOH, Six/One
seems to provide exactly that complementing Shim6)


I was looking at the bigger picture of helping the Internet as most
people use it today keep operating while a new router-based (a small
subset of routers) architecture is progressively introduced to limit
the 220,000 and growing load of prefixes on all the DFZ routers.
not sure i buy that one. IMHO it is way much harder to update the routers than updating the hosts. I mean, windows update does it for you (either you like it or not) 



Shim6 and Six/One are not solutions to that problem.
by definition thy are not, since you are specifically constraining to router based solutions. It is perfectly ok to explore this part of the solution space, though 


They may well
be solutions to the long-term architectural problems of the Internet
*if* most users adopt IPv6.  I can't imagine how this would occur in
the next ten or fifteen years.



i agree that deployability is the crux of the problem

i agree that shim6 deployment is a great challenge

not sure if other approaches will make this easier though
For instance, i would like to understand the incentives for ISPs to deploy anycast itrs 


I know some people feel very positive about IPv6, but I find it hard
to be enthusiastic.
i certainly agree that supporting v4 identifiers is a great advantage, but there are others deployment issues to be dealt with. 


regards, marcelo


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