Subject: Group Membership TTL

From: Joao Carlos Mendes Luis <[email-masked]>
Date: Thu, 14 Aug 1997 00:33:02 -0300 (EST)

Hi,

  Sorry if this is a basic thing, but I can't see how I could limit
group memberships in a restricted area.  It seems to me that group
membership is propagated all over the world, even for small ttl
conferences.  Is this really true ?

					Jonny

--
Joao Carlos Mendes Luis			[email-masked]
+55 21 290-4698				[email-masked]
Universidade Federal do Rio de Janeiro	UFRJ/COPPE/CISI
PGP fingerprint: 29 C0 50 B9 B6 3E 58 F2  83 5F E3 26 BF 0F EA 67

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From: Ajit Thyagarajan <[email-masked]>
Date: Thu, 14 Aug 1997 10:11:06 -0400

>conferences.  Is this really true ?

No, group membership is not propagated all over the world.  Group
membership reports are sent with a ttl of 1, so only the first-hop
routers know of the presence of group members.  However, group members
may be present anywhere in the multicast-connected world.  Similarly,
the sender to a multicast group that can "potentially" be anywhere in
the multicast connected world (subject to some constraints such as
ttl, scoping rules, etc.)

You can use "scoped group addresses" to limit the range of a multicast
group.  Multicast traffic sent to a scoped group is restricted to only
those subnets defined within the scope boundaries.  See the draft on
"Administratively Scoped IP Multicast"
<draft-ietf-mboned-admin-ip-space-03.txt> for details on scoped
groups.

Ajit

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From: Andre Uratsuka Manoel <[email-masked]>
Date: Thu, 14 Aug 1997 13:00:28 -0300 (GMT-0300)

->	Joao Carlos Mendes Luis wrote:
->
->  Sorry if this is a basic thing, but I can't see how I could limit
->group memberships in a restricted area.  It seems to me that group
->membership is propagated all over the world, even for small ttl
->conferences.  Is this really true ?
->

	Hi, Jonny

	In DVMRP, routers have to know about membership only if multicast
packets for the specific group get to them. If scoping and ttl rules don't
permit packets to pass to a router, that router will not even know the
group exists.

	Regards,
	Andre