Re: NHRP question

[Joel Halpern <[e-mail]>]

Last time I spoke to Yakov about the router to router case, his goal was to
eliminate all unsafe router-router cases.  There are safe cases.
The intend of the combination of Q, S, and B bits was to identify the
applicable cases.

The general goal was to be able to tell if the requestor was a host
or router, and whether the responder was someone it was safe for the
requestor to talk to.  

1) It seemed useful to distinguish between the "stable" case identified
by the "B" bit, and the more specific case when the responder is a
directly attached host.  Clearly it is not critical.

2) One could say that a source equivalent of the "B" bit would be better
than the "Q" bit.  It would be more general.  However,
    Most of us are probably assuming that information learned on behalf
    of one source can be used for/with other sources.  
If that is true, then the fact that a specific request is on behalf of
an on-subnet host is not particularly important.  Therefore, what is
needed to detect safety is the Q bit.

In particular, an interdomain request is safe if the Q bit is on in the
request, or the B bit is on in the response.  We could get rid of the S
bit, although I think it is a useful subset of "B" to identify.

Fortunately, in no case do any of these bits need to be adjusted hopwise
through the fabric.  Domain Boundary crossing is a state that must be
indicated, but it is separate from these bit settings.

Yours,
Joel M. Halpern				[e-mail]
Newbridge Networks Inc.