Re: [narten@us.ibm.com: PI addressing in IPv6 advances in ARIN]

[Scott Leibrand <sleibrand@internap.com>]

On 04/16/06 at 10:59pm -0400, Igor Gashinsky <igor@gashinsky.net> wrote:

> [1] Those requirements, which shim6 currently fails to meet, again, are:
> 1) equal or better TE capabilities to PI multihoming in IPv4
> 	a) those capabilities controlled site wide, not host-wide
> 	b) those capabilities covering all deployment scenarios that IPv4
> 	   currently covers and people use heavily (ie inbound/outbound
>     	   TE, transit TE, partial routes TE, peering TE, etc)
> 2) equal or better convergence around failures as IPv4 ie (1st packet
> 	shim)
> 3) do all that without an undue burden on the server/SLB/proxy device

Igor (and Patrick),

I understand that shim6 doesn't provide a solution for content providers'
multihoming needs.  IMO that's one of the reasons we had to go ahead with
PI.  However, I wonder how you (and Patrick) would feel about continuing
to use PI space in IPv6, and also supporting shim6 to allow the end users
you're communicating with to multihome?  In my mind, the balance point
would be to configure your servers to not initiate shim6 capability
negotiation, to allow negotiation if the client initiates it, and to
promptly discard shim6 context after capability negotiation is complete.

If you were to do something like that, it seems to me that you would incur
very little cost, as most multihomed clients would never even initiate
shim6 capability negotiation due to short session duration.  Those that do
would only require you incur the processing overhead to deal with those
packets: once the negotiation is complete you can safely discard the
resulting state.

The only time this type of shim6 support would require additional state
tracking on your side would be when a multihomed client experiences a
failure, initiates reachability exploration, prompts context
re-establishment, and then re-homes to a working locator pair.  This is
likely to be rare, and when it does occur the additional state is allowing
you to successfully complete a transaction that would otherwise fail.

TIA for your thoughts,
Scott