Re: Final rolc minutes

["Eric W. Gray" <[e-mail]>]

Joel,

You wrote:
> 
> I was just re-reading the NHRP draft, and thinking about some routing issues.
> I am concerned about the use of the Source NBMA and Source Protocol Address
> fields in the request.
> 
> Two cases come to mind:
> 1) The routing protocol is BGP.  The outward path does not have a policy
>    restriction on shortcuts, but the assymettric reverse path does.
>    (Someone is being very "careful" about what paths they advertise.)  As
>    currently defined, the destination can learn the sources ATM address,
>    and attempt to establish the VC to him anyway, avoiding the fact that
>    an NHRP request in the reverse direction would hit a policy terminator
>    who would respond with his own address.
> 2) The station issuing the query is doing so on behalf of a bridge-like
>    device which is the actual ingress to the ATM.  (Yes, there is some
>    clever layering here.  Come to MPOA for fun and confusion.)  As such,
>    the internetwork source address is the routing entity issuing the
>    query request.  However, in order to cause VCs to match up properly,
>    the ATM level source address is that of the bridge-like device which
>    will make use of this information.  Therefore,
>    A) caching this pairing will not produce good information
>    B) sending the response over an existing short-cut will be problematic.
> 
> Comments?
>

I believe that the concept of a logical NBMA subnetwork prevents the first
problem.  The second paragraph from the top of page 7 states that NHRP query
and response messages cannot cross logical NBMA subnet boundaries and - from 
my reading - NBMA logical subnets are defined in suchg a way that an extant
policy terminator IS the NBMA logical subnet boundary.

The first paragraph at the top of the same page implies that a response must
be sent back to its originator based on source protocol address which should
eliminate 2B.

Perhaps wording should be inserted in section 2 to the effect that an NHS may
have multiple NBMA addresses (may be deployed as a distributed implementation)
and not all of these addresses may be appropriate when communicating with the
NHS entity identified by the source protocol address - consequently, caching
of source protocol and NBMA address pairs in Next Hop Resolution Requests is
not permitted.  This should address the concerns you have with 2A above.

>
> Thank you,
> Joel M. Halpern                         [e-mail]
> Newbridge Networks Inc.

--
Eric Gray