Re: [DNA-BOF] Using L2 to provide Instantaneous MD & ND

[Greg Daley <greg.daley@eng.monash.edu.au>]

Hi Bernard,

Bernard Aboba wrote:
>>Personally, I think Optimistic DAD is good enough.
>>If this is the case, there's no need to expend so
>>much effort on L2 solutions.
> 
> 
> I agree. In the case where the host remains on the same subnet,
> reachability can be confirmed in a single roundtrip to the gateway.  As
> we've discussed, this typically cannot be avoided anyway, but in many
> cases it is not costly -- latencies on the order of 1 ms are achievable on
> 802.11 networks.
> 
> The expensive case is where the host has changed subnets but does not
> know this, fails the reachability test, and then has to obtain an
> address, potentially on a network on which it already has a valid IP
> address.  Latency arises from having to retry the reachability test
> in case of packet loss, as well as from having to obtain an address
> unnecessarily.  The latter cost is substantial for stateful address
> configuration where the host may have to communicate with a DHCP server.
> 
> If "hints" can help avoid this case then the contribution is substantial.
> 
I agree, but the discussion with Paul was
regarding whether DAD optimization could be
achieved through the L2 assistance.

Once again, we have the detection vs. configuration
issue.  Certainly L2 information should be passed into
the detecting system, since it can help avoid some of the
situations which you mentioned.

Greg