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Re: [dhcwg] Clarification regarding Dhcpv6 Vendor-specificoption (option 17)



On Wed, Mar 11, 2009 at 05:17:13PM +0530, ravi kumar wrote:
> Incase if client requires only specific Vendor Option from Server, Can
> Vendor-specific option  be used for this purpose?

I may not understand the question.

The only thing that causes a VSIO to be included in reply is if the
VSIO option code is on the ORO.

However, a server might select which /specific/ VSIO options (which
enterprise-ID or specific sub-option contents) to send based upon
contents of any VCIO options, or as Bernie stated, a VSIO sub-ORO,
depending upon the vendor's specification.

So for example if a client sends VCIO enterprise ID's A and B, and
the server is configured with values for enterprise ID's B, and C,
then in this case if the client placed VSIO on its ORO, the server
may only reply with VSIO for enterprise ID B only (having no config
for C).  A different (simpler) server may instead reply with
enterprise ID's B and C, if the server has no mechanism to distinguish
specific ID's, even though the client can make no use of VSIO for ID
C.

Note that in some cases (in DHCPv4), vendor-class would be specified
to be in the reply made by the server, so that the server's reply can
be versioned (and the client can behave differently for newer or older
servers).  This should probably be deprecated, and a better technique
if required would be to put a version option in the VSIO contents.

> For instance: options x and y are vendor options defined on Server. Can
> Client just request option X, by including only option x in VSIO option?

No.  As Bernie says, some VSIO options do provide a sub-ORO, but the
presence of VSIO options will not guarantee a similarly-identified
VSIO is included in the reply.

> What would typical Server implementations be, in this case.

ISC's implementation is very simple right now - we reply with all VSIO
that are configured within the client's scope, IFF the client placed
VSIO on the ORO.

> I just want to confirm, if  VSIO can be used for Vendor options, in similar
> fashion of how ORO is used for requesting specific standard options
> configured on Server.

Only the ORO determines what options the client may reasonably expect
in reply (with some "core DHCPv6 protocol layer" exceptions).

-- 
David W. Hankins	"If you don't do it right the first time,
Software Engineer		     you'll just have to do it again."
Internet Systems Consortium, Inc.		-- Jack T. Hankins

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