Re: [DNA] No FastRA unless Landmark? (draft-pentland-dna-protocol-00)

[Sathya Narayanan <sathya@research.panasonic.com>]

Greg -

> 
> In section 5.1.5, the proposal says:
> 
> "If the source address of the Router Solicitation is the
>  Unspecified Address or if it does not contain a landmark option,
>  then the router builds a CompleteRA and schedules it for multicast
>  transmission as per RFC 2461.  The interface MUST remain in the
>  UnicastSender state."
> 
> Is it intended that hosts which don't divulge their previously
> attached prefix in a RS landmark option aren't provided with FastRA service?

No. 

Looks like there are two reasons why a host will not include a landmark option (I thought about only the first):
1) Host is a non-DNA host
2) Host doesn't want to divulge their landmark

The text in the draft is targetted at the first case, i.e. if the RS message doesn't have a landmark option it is a non-DNA host. The only way to help out the host is by sending a CompleteRA because the router doesn't not know what question to answer. For a non-DNA host, a completeRA will be only partially helpful, if it hasn't moved link and sees its current prefix in the completeRA in a PIO - because it can neither recognize the completeRA bit nor the DNAO. Sending too-many unicast CompleteRA with the hope that it is useful for the host is not good for link-utilization and hence the recommendation.

Now, I think, the same logic applies for the second case too, even though a DNA-host could receive better benefit from the CompleteRA. The router has no-way of knowing whether the sender is a dna-host or not.

So, the question is do you (WG) think that it makes sense to respond with a CompleteRA message every time a RS message without a landmark arrives. IMHO, no.

regards,
Sathya