RE: ND (NUD) on ISATAP links

Hi Jason,

Thanks for the comments.

> > 
> > > 
> > > The scalability problem you mention only happens when there are
> > > very few routers serving a lot of hosts.  In that case, a 
> > > particular router
> > > is more likely to be picked as a next hop and NUD will be run 
> > > after the
> > > AdvReachableTime has expired. The consuption of resources on 
> > > that ISATAP 
> > > router will roughly equivalent to a normal IPv6 router in 
> a similar 
> > > configuration (+ the extra is a tunnel overhead) so I don't 
> > > see a large 
> > > problem with scalability.
> > > 
> > > 
> > 
> > 
> > As I understand it, there are two sides to this question.
> > 
> > In the above, the resources that you speak about 
> > are the resources needed at a particular ISATAP
> > router in order to _participate_ in NUD
> > performed by its ISATAP host (responding to NS's).
> 
> The scalability problem is rooted in the fact that each ISATAP
> host will have to send a unicast NUD to the router (as opposed to
> multi/broadcast in the case of a "normal IPv6 router).  Thus 
> ISATAP hosts   
> can not passively listen for NA's, they must initiate a 
> unicast NUD every
> AdvReachableTime.  As opposed to the "normal IPv6 router" 
> case, more NS's
> would actually be sent and processed by the ISATAP router.
> 

Agreed. 

In order to limit the NS/NA signalling then
one could recommend ISATAP routers to specify
an AdvReachableTime greater than REACHABLE_TIME (30 msec)
e.g. something in line with the 15 mins suggested for MinRouterSolicitInterval.

> 
> > Another concern is the scalability issues in relation to 
> the resources
> > needed at the ISATAP router in order to _perform_ NUD on its ISATAP
> > neighbours - Do we agree that this has been ruled out - i.e. that
> > performing NUD only is going to be demanded of ISATAP hosts 
> - or do we
> > want a LAN-like IPv6 functionality on ISATAP routers ?
> 
> It seems that if NUD is to be implemented at all, the only 
> place it could
> happen is the at the host.
> 

Agreed. The keyword here seems to be "if NUD is to be implemented at all".

Karen