Subject: RE: Deployability/Useability of Multicast [was: Re: PPP and Globa l Addresses ]

From: "Bernie Volz (EUD)" <[email-masked]>
Date: Mon, 18 Mar 2002 13:19:35 -0600

DHCPv6 only requires link-local multicast not site or global. From draft-ietf-dhc-dhcpv6-23:

7.1. Multicast Addresses

   DHCP makes use of the following multicast addresses:

      All_DHCP_Agents (FF02::1:2) This link-scoped multicast address
                        is used by clients to communicate with the
                        on-link agent(s) when they do not know the
                        link-local address(es) for those agents.  All
                        agents (servers and relays) are members of this
                        multicast group.

      All_DHCP_Servers (FF05::1:3) This site-scoped multicast address is
                        used by clients or relays to communicate with
                        server(s), either because they want to send
                        messages to all servers or because they do not
                        know the server(s) unicast address(es).  Note
                        that in order for a client to use this address,
                        it must have an address of sufficient scope to
                        be reachable by the server(s).  All servers
                        within the site are members of this multicast
                        group.

The All_DHCP_Servers is not a requirement to make the protocol work. It is usable in two cases:
- For Information-Request messages to avoid the need for relays. But, the All_DHCP_Agents is usable with relays.
- For auto-configuration of relays - if a relay doesn't have a configured DHCP server to forward packets to, it can forward them to the ALL_DHCP_Servers address.

So, DHCPv6 MUST have link-local multicast.

- Bernie Volz

-----Original Message-----
From: Bob Hinden [mailto:[email-masked]]
Sent: Monday, March 18, 2002 12:36 PM
To: Thomas Narten
Cc: [email-masked]
Subject: Re: Deployability/Useability of Multicast [was: Re: PPP and
Global Addresses ]

Thomas,

>1) Do people think that the existance of multicast within a site
>    (e.g., home, enterprise, etc.) can be assumed?
>
>    Note: I'm assuming link-local multicast will always work, the
>    question is whether wider scope (beyond neighboring routers)
>    multicast is available.

As much as I would like to see it otherwise, except for link (and maybe 
subnet) scoped multicast, I don't think we can assume multicast across a 
wider scope.  I suspect it will be more the exception than the norm.

>2) If the answer is "can't assume multicast is present", what should
>    be done about it. e.g.,
>
>    - What are the barriers that are preventing multicast from being an
>      assumed part of the infrastructure? What is needed to remove
>      those barriers?

Don't we have a whole working group dealing with this (e.g., mboned)?

It's a complicated mixture of routing protocol scaling, lack of agreement 
of inter-domain routing protocols, lack of interoperability between vendors 
of multicast routing protocols, few compelling applications that need 
multicast that can't be meet with unicast, etc.  There are a few places 
where it is used (i.e., financial industry), but as far as I can tell it's 
not widely adopted much beyond that.

>    - Which infrastructure protocols does IPv6 rely on that assume the
>      existance of multicast, and how are they limited if multicast is
>      not available?

Off the top of my head, DHCPv6 and Router Renumbering.

Bob

--------------------------------------------------------------------
IETF IPng Working Group Mailing List
IPng Home Page:                      http://playground.sun.com/ipng
FTP archive:                      ftp://playground.sun.com/pub/ipng
Direct all administrative requests to [email-masked]
--------------------------------------------------------------------

---

From: JINMEI Tatuya / 神明達哉<[email-masked]>
Date: Wed, 20 Mar 2002 15:35:00 +0900

>>>>> On Mon, 18 Mar 2002 13:19:35 -0600, 
>>>>> "Bernie Volz (EUD)" <[email-masked]> said:

> - For Information-Request messages to avoid the need for
>   relays. But, the All_DHCP_Agents is usable with relays.

> - For auto-configuration of relays - if a relay doesn't have a
>   configured DHCP server to forward packets to, it can forward them
>   to the ALL_DHCP_Servers address.

That's true.  However, "relay does have a configured DHCP server" is a
strong assumption (especially in a large scale network), DHCPv6 quite
relies on multicast (whose scope is larger than multicast).

					JINMEI, Tatuya
					Communication Platform Lab.
					Corporate R&D Center, Toshiba Corp.
					[email-masked]
--------------------------------------------------------------------
IETF IPng Working Group Mailing List
IPng Home Page:                      http://playground.sun.com/ipng
FTP archive:                      ftp://playground.sun.com/pub/ipng
Direct all administrative requests to [email-masked]
--------------------------------------------------------------------