Re: shim header in every shimmed packet

[Iljitsch van Beijnum <iljitsch@muada.com>]

On 13-okt-2005, at 4:48, Erik Nordmark wrote:

> > Right. I haven't thought much about the issues around locator   
> > updating because I was kind of assuming this wouldn't happen in  
> > the  presense of HBA.

> But it can with CGA.

Yes. I know this assumption was wrong.  :-)

> > > Any ideas on how to do this?

> > That would be something that we explore in the "how to safely   
> > suppress the shim header after rewriting" document but in the  
> > case  where the locator sets for the different ULIDs are disjoint  
> > this  isn't an issue: the receiver without state that receives a  
> > shimmed  packet without a shim header will know this because the  
> > packet is  addressed at a locator-only address. It can then either  
> > send back a  shim error or an ICMP error.

> Yes, but I thought we wanted the capability to do this in other  
> cases than the disjoint case (I've never been a fan of each host  
> that has N ULIDs needing to create (N*N - N) extra locators).

That's not a problem: if having n(n-1) locators is the only way that  
the shim header can safely be suppressed (I suspect there are other  
ways but maybe not) then there is a tradeoff between either having n 
(n-1) locators and no shim header after a rehoming (unless there are  
other complications such as extra headers), or having n locators and  
having a shim header in packets after a rehoming event.

> It seems to me that we can't make sure the we got the handling of  
> the "bit" correct until we know how the sender and receiver will  
> use this capability.

I'll be happy to write a draft...

Iljitsch