Subject: DHCPv6 and Relay-to-Server Multicasting ...

From: "John Spence, CCSI, CCNA, CISSP" <[email-masked]>
Date: Sun, 23 Jan 2005 14:44:36 -0800

I posted this question on the IETF DHC Working Group list, but got no
response - thought I might ask here as well.

---------- question ---------

Does DHCPv6, using site-local multicast support for the relay-to-server
traffic (FF05::1:3), assume that the servers are running MLD, and that there
is a multicast RP in the network - as would be common for more traditional
multicast applications (like one-to-many video streaming)?  I see in the RFC
that the relays *may* be configured with the unicast addresses of the
servers, but they need not be - and the default is to use the site-local
multicast capability.

I'm envisioning this scenario.  Suppose we have 1000 DHCPv6 clients, and a
100 vLAN network, with DHCPv6 servers in the core and relays around the
edges.  Suppose we have 100 relays and 3 servers, and we'll assume that the
relay support is not built into the routers - the relays are standalone
platforms.

I do not see any way to get site-local multicast packets from the relays to
the servers without an end-to-end traditional MLD/PIM multicast-enabled
infrastructure.  Is that right, or is there another mechanism at work here,
or another document that covers how DHCPv6 and IPv6 multicast are related?

----end-----

Thanks for any clues or pointers.

John Spence
----------------------------------------------------
John Spence, CCSI, CCNA, CISSP
Native6, Inc.
IPv6 Training and Consulting
[email-masked]
www.native6.com
----------------------------------------------------

---

From: Brian Haberman <[email-masked]>
Date: Mon, 24 Jan 2005 08:04:51 -0500

Hi John,
      The use of a site-local multicast address will require a multicast
infrastructure.  That could be something as complex as managing
an RP-based multicast routing infrastructure.  It could also be done
using MLDv2 and SSM routing.  And in one scenario, I have seen
*static* multicast routes for DHCPv6 servers.

      So, in short, a multicast infrastructure is needed when using
FF-5::1:3.  It is up to the deployer to determine the complexity of
that infrastructure.

Regards,
Brian