Subject: [magma] MSNIP capabilities announcement and MRD

From: Jim Martin <[email-masked]>
Date: Mon, 1 Mar 2004 23:40:20 -0800

Gentlepeople,
	In a discussion after the meeting, it came up that using MRD to 
announce MSNIP capabilities poses a fundamental problem, since we're 
now sending MRD messages to the new "All-Snoopers" group. Since the end 
hosts presumably wouldn't join this group, they wouldn't get the 
information. If all hosts join the group, we might as well just use 
All-Systems.

	What this brings up is the question of what the scope of MRD should 
be. If it's just for switches to learn who the current multicast 
routers are, and what some of their configuration values are, then 
carrying MSNIP is out of scope. If the scope is to carry a wide variety 
of information about multicast routers to all hosts (including 
switches) on-link, then we should revert to using All-Systems and 
definitely need the extensible options mechanism.

	My personal position is that MRD should have the more limited scope, 
solving the problem for switches.  We have other mechanisms (DHCP, RA, 
etc) to provide configurations to end hosts.

	Opinions?

	- Jim

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From: "Dave Thaler" <[email-masked]>
Date: Wed, 3 Mar 2004 22:25:35 -0800

Jim Martin writes:
> >> Given that, we need to go back and look at how to offer MSNIP
> >> functionality without piggy-backing it on MRD.  Are we looking
> >> at a RTS/CTS-like set of messages?
> >
> > Could this be plugged on top of IGMP/MLD messages similar to MRD
was?
> > Seems like a logical place..
> 
> 	Oddly enough, that was the subject of a discussion that Brian,
> Isidore
> and I just had. I was proposing a new IGMP/MLD message with the
> explicit goal of distributing multicast router specific information to
> all hosts. It would probably have a TLV format to allow various types
> of information (MSNIP being the first) to be sent.

We currently have several protocols that have TLV options which
could conceivably carry the information, including:

1) DHCPv4/v6
2) IPv6 Router Advertisements
(and probably more)

We should first evaluate whether existing ones are sufficient before
creating yet another protocol to give config parameters to hosts.
If they are not, we would then need to justify whether we need
another generic one, as opposed to making MSNIP self contained.

So one question to think about is whether a piece of information is:
a) specific to each router, such that different routers telling
you different information is fine.  An example of this is the 
preference in IPv4/v6 Router Discovery.  MRD fits into this bucket
since the information is essentially the router's IP address and
location.

b) specific to the link, such that all nodes on the link must use
the same information, but different links in the same network can
be different.  An example of this is the IGMP querier version.

c) specific to the network, such that all links in the same domain
use the same information.  An example of this is the DNS server 
addresses.

For type (c) information, DHCP is the standard answer.
For type (a) information, RAs are the standard answer in IPv6.
There is no extensible answer in IPv4 that I can think of
(IPv4 Router Discovery and MRD are not extensible).
For type (b) information, the line is more fuzzy - there are
examples using RAs and there are examples using DHCP where the
answer depends on the link of the host.

-Dave

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From: "Dave Thaler" <[email-masked]>
Date: Wed, 3 Mar 2004 22:25:35 -0800

was?

1) DHCPv4/v6

-Dave