Re: Comments on draft-bagnulo-multi6dt-hba-00.txt

On 17-nov-04, at 21:42, Mohan Parthasarathy wrote:

>> What do you see as the benefit of having the same
>> iid for all prefixes?

> None :-) I was only trying to find out the reason
> as to why this can't be done or easily supported
> without changing the format.

There are two reasons it is good to have the same IID for different 
prefixes:

1. At some point in the future, we may want to have routers rewrite the 
prefix part in the source addresses of outgoing packets. This is a very 
good way to deal with ingress filtering. However, it is unlikely that 
routers could hold all the state necessary to match individual 
addresses rather than prefixes. (Note that we are NOT proposing router 
rewriting at this point.)

2. Easier debugging.

The reason you can't have the same IID in different prefixes for CGA is 
that in CGA the prefix is part of the data the hash is computed over. 
The reason the prefix is included is because otherwise someone could 
precompute all possible hashes.

It would be possible to include one chosen prefix rather than the 
"real" prefix, though. This way out of N addresses there would be one 
that is SEND-compatible and N-1 that aren't. The SEND-compatible 
address could be the ULID. Not having SEND for additional locators 
wouldn't be too much of a hardship, IMO.