RE: [dhcwg] Leasequery: should it be standardized?

["Woundy, Richard" <[e-mail]>]

Folks,

I don't know the outcome of this thread, after the flurry of comments in
support of the DHCP Lease Query functionality -- which included some useful
comments to improve the next draft version.

Today, as a fairly large cable service provider, I use DHCP Lease Query
between distinct vendors of DHCP servers and DOCSIS CMTS relay agents, where
it provides great value -- preventing IP address theft among subscribers. In
places where I cannot yet deploy this technology, some legitimate
subscribers have to use some ugly workarounds (e.g. continuously pinging the
first-hop router) in order to defend their legitimately-assigned DHCP
address lease. The Lease Query functionality exists in multiple vendor DHCP
server implementations and multiple vendor (CMTS) relay agent
implementations. Today, these vendors tend to use the documentation of the
Lease Query protocol from the Cisco website.

While I believe that Lease Query should be standardized within the DHC WG, I
am not sure I would refer to this functionality as "access control".
Performing source IP address verification is one small piece of router
access control. To see the full ugliness of access control from the DiffServ
perspective, see RFC 3289 -- this extent of functionality is way beyond the
charter of DHC.

I don't think we should extend Lease Query to be a generic DHCP server
lookup protocol. For example, if a non-relay agent needs to know the lease
database information from a DHCP server, it should query the DHCP Server MIB
<http://www.ietf.org/internet-drafts/draft-ietf-dhc-server-mib-08.txt> --
which incidentally I believe now is ready for WG last-call.

So perhaps some re-wording of the problem statement, and perhaps some
pruning of functionality that has crept into the draft, is in order.

I am sorry I did not respond to this thread sooner, but I have been
overwhelmed with other IETF discussion threads. DiffServ and DHCP Server MIB
come immediately to mind. ;^)

-- Rich

P.S. I remember the original intent of Lease Query -- since I first pitched
the Lease Query idea (aka "Third-Party DHCP") back in April 1998,
<http://www.ietf.org/proceedings/98mar/98mar-edited-51.htm#P6021_315505>. In
fact, I still have the original slide deck on my laptop. ;^)

-----Original Message-----
From: Kim Kinnear [mailto:[e-mail]]
Sent: Wednesday, February 26, 2003 12:37 PM
To: [e-mail]
Cc: Ralph Droms; Thomas Narten; Kim Kinnear
Subject: [dhcwg] Leasequery: should it be standardized?



Folks,

We have come to something of a impasse on the leasequery draft,
and I need *your* support if you believe we should continue to
pursue this draft.

===============================================================
Without considerable support from the DHC WG, we will halt work
on the leasequery draft and all attempts to bring this work to
standard status.
===============================================================

If you believe that there is any value in standardizing the
leasequery capability, please at least respond to this list ASAP
with your positive support.

If you have the time and expertise, please read the rest of this
email and see if you can offer cogent arguments as to why this is
work that the DHC working group should be pursuing.

If we don't standardize the leasequery capability, each vendor of
access concentrators and DHCP products that wish to use this
approach will then need to work together (possibly in some other
forum) to try to get their products to be compatible.  Of course,
it may well be that we are the only folks who see this as a
useful capability, and so that may not be an issue at all.

Thanks -- Kim

-----------------------  Summary -----------------------

In case you haven't been following the email between Thomas
Narten and myself, he has been questioning the problem statement
of the leasequery draft.  Ralph proposed a new problem statement,
but Thomas feels that this whole capability is questionable.

You are invited to respond to Thomas' arguments, which I have
distilled as follows:

  1.  Doing anything in the DHC WG like supporting "access
  control in router type devices" is out of scope for the working
  group, and doesn't fit its current charter.

  2.  Access control in router type devices is not well enough
  understood to be sure that:

	a) leasequery is the right solution.

	b) any DHC-based approach is the "right" approach to
	solve this problem.

  3.  Until we are sure of 2(a), then we should not proceed with
  this work (I believe that this statement is implicit in Thomas'
  comments.)

-----------------------  Background ---------------------------

Here is Ralph's proposed problem statement:

   Router-type devices which want to enforce some level of access
   control over which IP addresses are allowed on their links
   need to maintain information concerning IP<-MAC/client-id
   mappings.  One way in which these devices can obtain
   information about IP<-MAC/client-id bindings is through "DHCP
   gleaning", in which the device extracts useful information
   from DHCP messages exchanged between hosts and DHCP servers.

   However, these devices don't typically have stable storage
   sufficient to keep this information over reloads.  There may
   be additional information that is useful to the device that
   cannot be obtained through DHCP gleaning.  The leasequery
   request message described in this document allows a device to
   obtain information about IP<-MAC/client-id bindings from a
   DHCP server.  This information may include currently active
   bindings, bindings involving previously assigned addresses for
   which the lease on the address has expired and static bindings
   for devices that are otherwise configured and not using DHCP
   for address assignment.

Thomas' concerns center on the second paragraph above, and he says:

   Note, that above is pretty vague and doesn't say what
   information the access device needs.  It's hard to look at the
   problem statement and say "yes, I understand the boundaries of
   the problem" and then "and the solution seems like a good
   match for the problem".

   Popping up a level, how is it even appropriate for the DHC WG
   to be doing work on "access control in router type devices"?
   One can argue that work of this broad a scope is well
   out-of-scope for this WG (e.g., look at the recently approved
   charter).  I'm far from clear that work of this scope should
   be done in DHC or that the problem is well enough understood
   to conclude that DHC lease query is the right solution or that
   any DHC-based solution is the right one.  What about routers
   wanting to do access control that don't use DHC, for instance?

   And note, I'm not raising these issue just to be a PITA. These
   are questions that I expect that the IESG would ask if I
   brought the document forward.  Thus, I need to have reasonable
   responses to those questions.  Otherwise, I can predict the
   likely outcome.

My response to Thomas was:

   This approach to access control was developed by joint work
   with the folks building our access concentrators and several
   of us in the DHCP implementation group.  They found that the
   functionality delivered to actual users was of sufficient
   value to those users to be worth the cost of engineering this
   particular solution.  We supported them in moving the
   implementation forward.

   The solution was not based on the charter of the DHC working
   group either then or now -- it was based on a rather pragmatic
   approach to meeting the needs of users, which it has seemed to
   do.  In my view at least, it fits within spirit of the DHC WG
   activities, and was a logical extension of the those
   activities.

   It isn't a comprehensive approach to any sort of security (nor
   was it designed to be such) -- it is a supporting piece of
   technology to one limited form of access control.

Thanks for your interest in the leasequery capability.

Kim

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