Re: Thoughts about layering multi-addressing

[Pekka Nikander <pekka.nikander@nomadiclab.com>]

> On the other hand I'm not sure if you classification above
> is exact. Primary locators are used in SCTP, but do
> we need them in shim? Or did you mean "one current locator"?

I don't understand the difference.

> Also, some extensions in the interface appear unavoidable,
> like telling transport that it needs a slow start, or the ability
> of multihoming aware transports and applications to bypass
> the shim if they want to.

Agreed wrt sending events to the transports.

I am not so sure about the usefulness of a generic bypass mechanism.   
Diagnostic applications will require such bypass, for sure, and it  
will probably be a useful mechanism during a transition period, e.g.,  
for SCTP.

However, from an architectural point of view I think that the shim  
layer is exactly the right layer to share information about the  
available IP addresses.  The set of addresses is a property of the  
host, and therefore seems to belong to the upper part of the IP  
layer.  The more specific properties of a path (an address pair),  
like QoS and what protocols/ports are available, seem to belong to a  
upper layer, though.  Hence, from this point of view IMHO the shim  
should take care of distributing information about the addresses that  
belong to the same host while, in general, path discovery functions  
belong to the upper layers.

This was reflected also in the other mail with the "stepped" protocol  
model, where there is an additional layer between the "basic shim"  
and the unmodified ULs.

--Pekka