Re: Flow label versus Extension header

[Pekka Savola <pekkas@netcore.fi>]

On Mon, 25 Apr 2005, Erik Nordmark wrote:
> This isn't the only option. With receiver-based tag allocation, then 
> the receiver can choose which locators it advertises for which 
> contexts. For instance, a receiver can have multiple locators in 
> each prefix and keep them separate. So {P1:X, P2:Y} can use tag=1 
> and be associated with one context, and {P1:Z, P2:W} can use tag=1 
> and be associated with a different context. Of course, if the host 
> doesn't do this, then it can assign the tags to that it never needs 
> to look at the locators in order to lookup the context.

I'm a bit confused -- we're still talking about flow label and 
extension header/destination option both, right?

How would one perform receiver-based tag allocation with flow labels, 
because the flow label is allocated when the sender sends out a first 
packet and cannot be changed since?

Or are you assuming that with receiver based allocation, the receivers 
would keep some kind of internal shim6 mapping table which would map 
{source addresses, destination addresses, flow label} values to a 
shim6-specific context tag (which might or might not be provided to 
the apps as auxialiry data) ?

This would work as long as, (AFAICS)
 - the receiver knows which locators the peer has before receiving the 
first packet from a new locator (i.e., the earlier discussion with me 
and Marcelo that the sender can't just switch over to using a new 
source locator, it must be negotiated with the shim protocol first)

 - we don't care about the {src,dst,flow} clashes, the implementations 
do mitigating techniques to avoid them (they happen very rarely in any 
case), or there is a mechanism like you wrote which allows the 
receiver to reject adding a locator (or inform that shim6 won't 
work with that particular locator at least for the moment)

And the general assumption of shim6 is,
 - the implementations' port number space is unique across all the IP 
addresses, so that there can't be two apps sitting at a port at two 
different IP addresses.  Otherwise the shim would end up having to 
rewrite ports as well and that wouldn't be good.

--
Pekka Savola                 "You each name yourselves king, yet the
Netcore Oy                    kingdom bleeds."
Systems. Networks. Security. -- George R.R. Martin: A Clash of Kings