> From: Margaret Wasserman [mailto:[EMAIL PROTECTED]] [...] > I'm not talking about the limited way in which the "subnet-local" > multicast scope works today, but about the definition of a subnet. > > The word "subnet" means a group of nodes that share a common global > prefix, including subnet ID. The fact that we don't have a multicast > mechanism to successfully reach this group of nodes doesn't change > the definition of "subnet". > > So, a subnet may include all of the nodes on a single link -- this will > be the most common case, where all of the nodes are generating addresses > from a single set of RAs. > > A subnet may also include a subset of nodes on a single link, if there > is more than one prefix in use on the link, and not all nodes use all > of the prefixes.
All of them have interfaces in the subnet scope zone, regardless of whether or not they use addresses in the subnet prefix. > Iff we adopt the multi-link subnet proposal, a subnet may also include > a set of nodes that share a subnet prefix across multiple links. Still > without any requirement that the subnet contain all of the nodes on > each link. But still true that all of those nodes have interfaces in the subnet scope zone regardless of what addresses they have. > I agree that it would be quite tricky to use an IPv6 multicast address > to reach a particular subnet, given how multicast addresses are > constructed. There is no way for a given node to determine whether > a subnet-local multicast is intended for any of its subnets. I disagree. Nodes don't have subnets, nodes have interfaces and addresses. There is a way for a given node to determine whether a subnet-local multicast is intended for any of its interfaces, which is that it's intended for it if the node has joined that subnet-local multicast address on a given interface. > Besides, > as Pekka pointed out, none of the nodes on the link will have joined > the subnet-local multicast group, so the traffic actually won't reach > any of them. Eh? It will reach all of them, and will be received by the IPv6 layer as long as it has joined the group. If it hasn't joined the group, then it's not supposed to be received by that node. That's why it's called multicast, not broadcast. > IPv4 did have a concept of subnet-local broadcast (i.e. 128.224.4.255), > but the ability to address all of the nodes on a single subnet is > apparently lacking in IPv6. I don't consider this a big problem, Here we agree in concept, but I would nitpick with your terminology. IPv4 does not have a concept of "subnet-local" (as defined by the scoped Addrarch) broadcast, it's really network-prefix-local broadcast, and IPv6 doesn't have such a thing. > but > we shouldn't pretend that "subnet-local" multicast is possible, since > it isn't. "Subnet-local" multicast is indeed possible. "Network-prefix-local" multicast is not possible. -Dave -------------------------------------------------------------------- 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 PROTECTED] --------------------------------------------------------------------
