Subject: [dhcwg] I-D ACTION:draft-ietf-dhc-agent-vpn-id-02.txt

From: [email-masked]
Date: Wed, 06 Nov 2002 06:27:45 -0500

A New Internet-Draft is available from the on-line Internet-Drafts directories.
This draft is a work item of the Dynamic Host Configuration Working Group of the IETF.

	Title		: VPN Identifier sub-option for the Relay Agent 
                          Information Option
	Author(s)	: K. Kinnear, M. Stapp, R. Johnson, J. Kumarasamy
	Filename	: draft-ietf-dhc-agent-vpn-id-02.txt
	Pages		: 8
	Date		: 2002-11-5
	
In some environments, a relay agent resides in a network element
which also has access to one or more VPNs.  If one DHCP server wishes
to offer service to DHCP clients on those different VPNs the DHCP
server needs to know the VPN on which each client resides.  The vpn-
id sub-option of the relay-agent-information option is used by the
relay agent to tell the DHCP server the VPN for every DHCP request it
passes on to the DHCP server, and is also used to properly forward
any DHCP reply that the DHCP server sends back to the relay agent.

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From: Thomas Narten <[email-masked]>
Date: Wed, 06 Nov 2002 15:54:16 -0500

Looking  through this document, could someone explain what problem
this ID is solving?

In particular, it seems to me that DHCP servers/relay agents shouldn't
and don't need to understand about VPNs.  I.e., when a node joins the
network, it is assigned a VPN. This ID proposes that a relay agent
include a string or other identifier in the relay agent option to
indicate the VPN the client is assigned to. But, it seems to me that
the relay agent could just as easily be assigned an IP address on each
VPN, and then just stuff that address into the giaddr field of the
packets. This is normal DHC, using existing protocols and standards.
In this case, neither the relay agent nor the DHC server need to know
about VPNs in any way other than they already do. I.e, the giaddr
field indicates a VPN, and existing standard DHC config technique can
be used to assign addresses and other paramaters to the client.

What is it that I'm not understanding here?

Thomas
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From: John Schnizlein <[email-masked]>
Date: Wed, 06 Nov 2002 16:22:56 -0500

When a service provider has several customers using net-10, 
but a single DHCP server, it needs to discriminate among them.
If the network device closest to the customer is configured with
the VPN identifier for that customer network, the DHCP server
can manage pools for each VPN independently.

John

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From: Ted Lemon <[email-masked]>
Date: Wed, 6 Nov 2002 15:35:17 -0600

> But, it seems to me that
> packets.

You don't even need to do that - you can just use the relay agent 
subnet selection option!

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From: Thomas Narten <[email-masked]>
Date: Wed, 06 Nov 2002 22:33:17 -0500

> but a single DHCP server, it needs to discriminate among them.

Ah. It would be good if the ID said that.  

> can manage pools for each VPN independently.

So, the key requirement is for the relay agent to indicate which
customer or "address realm" (using NAT terminology) the request it is
relaying comes from. Using VPN IDs is one way, but it only works if
VPNs are used. Seems like a more general approach would be
desireable. I could imagine the same issue coming up in environments
where just IP (or IPsec tunnels) were used, in which case no L2 VPNs
would be available.

Why can't you use something like the Agent Circuit ID Sub-option
(sub-option code 1)? You could stuff  an identifier in there to
indicate which "VPN" to use.

Thomas