DHCPv6 Relay Agent Link Selection(RALS) Option

Amy:

Bud, David, and Ted all share the same concern I have,
though they
expressed it better.

You are trying to have the relay make decisions that are
better left to
the server. We usually assume that the DHCP server is the
place where
complexity lives and many servers (as David pointed out for
the ISC
server and we have similar facilities in the Cisco Network
Registrar
server) already provide mechanisms to do this -- either for
specific
(preconfigured) clients or based on information (from client
or relay)
in the packet.

If you put this information in the relay, you've got to
configure it and
also any other relays that those clients may use. Generally
there are
many relays for each DHCP server.

If you put this information in the DHCP server, you've got
fewer
"devices" to configure and update as changes are
made.

And, DHCP servers usually run on general purpose hosts and
have APIs or
other capabilities that are often lacking on relay agents
which are
typically on routers.

The bottom line is that as the relay must be configured with
some set of
rules (ie, POLICY) to apply to clients (so that it can set
your
link-selection option accordingly), we feel it better to
move that logic
into the DHCP server.

If you don't have rules (policy) but instead the relay is
extracting
this information from the network in some manner that is
unavailable to
the DHCP server, then I suggest we look at an option for the
relay to
communicate this information to the server so that the
server can apply
appropriate policy. That is a much more powerful system as
perhaps
others want to do more than just determine the prefixes to
assign.

You might look at what DOCSIS provides for DHCPv4 and DHCPv6
as a model
-- capabilities and other data are communicated to the DHCP
server so
that it can apply appropriate policy.

- Bernie 

-----Original Message-----
From: Amy Zhao [mailto:zhaoyupinghuawei.com] 
Sent: Thursday, September 21, 2006 5:07 AM
To: 'Bud Millwood'; 'David W. Hankins'
Cc: dhcwgietf.org
Subject: RE: [dhcwg] [New I-D] DHCPv6 Relay Agent Link
Selection(RALS)
Option

Hello!

Thanks.

Sorry, maybe I used an inappropriate example. I am not
trying to make
relay
agent dictate policy, I just want to express 
that the information the link-address provides is per-link,
and the
information that lin-selection option provides can be not
only 
per-link,but also per-client.

B.R.
Amy 

E-mail: zhaoyupinghuawei.com

> -----Original Message-----
> From: Bud Millwood [mailto:budmweird-solutions.com] 
> Sent: Thursday, September 21, 2006 4:03 PM
> To: dhcwgietf.org
> Subject: Re: [dhcwg] [New I-D] DHCPv6 Relay Agent Link 
> Selection(RALS) Option
> 
> On Wednesday 20 September 2006 17:14, David W. Hankins
wrote:
> > On Wed, Sep 20, 2006 at 04:51:41PM +0800, Amy
wrote:
> > >     But for some access policy, client A can
not be assigned the 
> > > address in prefix A, client B can not be
assigned the address in 
> > > prefix B. And in this case, onlu using
link-address is 
> not sufficient.
> >
> > Traditionally, when DHCPv4 installations have been

> presented with this 
> > problem, the determination of which subnet to
allocate to 
> the client 
> > has been made on the server side.
> >
> > That is, the server identifies the client (by
identifier or 
> contents 
> > of some options the client (or relay!) supplies or
similar) and 
> > allocates an address the client 'is permitted'. 
In ISC 
> DHCP we call 
> > these 'permit/deny' statements, and it is
generally done by 
> > 'class'ifying the clients into distinct groups
first.
> >
> >
> > There aren't any DHCPv6 traditions quite yet, but
is there 
> some reason 
> > you think this old DHCPv4 model is not going to
serve us in DHCPv6?
> >
> > It's my opinion that it would be easier to
configure the 
> (small number
> > of) DHCP Servers to do what is desired in this
situation, 
> and harder 
> > to configure the (larger number of) relays to
produce the 
> right subnet 
> > for each client.
> 
> I'd like to weigh in here and say that I generally
agree with 
> your conclusions David. It's not a bad thing for a 
> client/relay to provide a server with as much
contextual 
> information as possible, but there should be a
distinction 
> between providing contextual information and trying to 
> dictate policy. And I don't think relays should be
dictating policy.
> 
> - Bud
> 
> Bud Millwood
> Weird Solutions, Inc.
> http://www.weird-solut
ions.com
> tel: +46 8 758 3700
> fax: +46 8 758 3687
> mailto:budmweird-solutions.com
> 
> _______________________________________________
> dhcwg mailing list
> dhcwgietf.org
> https://
www1.ietf.org/mailman/listinfo/dhcwg
> 

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DHCPv6 Relay Agent Link Selection(RALS) Option

Thread: DHCPv6 Relay Agent Link Selection(RALS) Option