Hi Thomas, > -----Original Message----- > From: Thomas Narten [mailto:[email protected]] > Sent: Tuesday, December 01, 2009 1:54 PM > To: Templin, Fred L > Cc: [email protected] > Subject: Re: New draft on "Stub Router Advertisements in IPv6 > NeighborDiscovery" > > Hi Fred. > > the picture is a start...
OK. > "Templin, Fred L" <[email protected]> writes: > > > http://osprey67.com/stub-router.pdf > > > In this picture, the link I am concerned with is labeled > > "NBMA Link" in the diagram. > > Please add an indication for what a typical "site" is. Are all of the > stub networks considered part of the same site (i.e., same company, > same house, etc.)? In my picture, each stub network is a separate site. The NBMA link and all of its attached devices is also a separate site, so the provider-facing interfaces of all of the stub routers in the diagram are connected to the same site. (This is not to say that stub network "sites" cannot be multi-homed; they certainly can, but the drawing does not show examples of that in order to avoid excessive clutter.) > Also, you show "stub network 1", 2, 3, .etc. > > What is the internal structure of those networks (or does it matter)? It doesn't matter. > In particular, there are presumably multiple links present in a stub > network. Are there only "normal" routers internally? Normal routers and links, yes. But, each stub network could itself contain multiple internal NBMA links which would appear to be sites within themselves (or, "sites- within-sites"). Each of those "sub-sites" would have a set of default routers and a set of routers that appear as stubs within that site. In other words, the model is recursive. > Can a "stub" router only exist on the NBMA link? Do you mean, are NBMA links the only examples where one would find stub routers? I don't think so, but NBMA links are peculiar and may present challenges to ordinary routing protocols that are not as prevalent on "ordinary" links. > Can you provide a specific example of the kind of link technology you > are thinking of for the NBMA link? Is this DSL/Cable/ATM? Or just a > hypothetical NBMA link? And who runs the NBMA link? Is this not a link > operated by the Provider? One example is an ISP network that connects multitudes of CPE routers (i.e., stub routers) with a finite collection of gateways via IP-in-IP tunneling. ISATAP is an example NBMA link type that could be used in such networks. > I see there are "hosts" on the NMBA link. Can you provide examples of > what kind of hosts? (I guess I really don't understand the deployment > model you are assuming here... i.e., why wouldn't the NBMA link only > have routers on it, with all hosts being behind a router.) Take ISATAP for example. The hosts configure tunnel endpoints that connect to the ISATAP "link". Any device that supports ISATAP can connect to the NBMA link in this fashion, e.g., if there is no way for the host to connect behind an "ordinary" router. > > As you can see, there are stub networks connected to the link by > > stub routers, and default routers that connect the link to provider > > networks (which then connect to the Internet in some way). The link > > is intentionally shown as two segments joined together by "..." to > > show that it can be arbitrarily large and in some cases may contain > > hundreds, thousands, or even more stub routers and stub networks. > > OK. > > > >From the diagram, only those routers labeled "default router" > > should advertise default router lifetimes, M&O flags, PIOs, > > and other RA information that provides operating parameters > > for the link. If the routers labeled "stub router" also > > advertised those kinds of parameters, then any hosts labeled > > "host on NBMA link" would incorrectly update their link > > parameters. As a simple example, if a router labeled "stub > > router" advertised a non-zero default router lifetime in > > an RA that was heard by a host labeled "host on NBMA link", > > then the host would incorrectly configure a default route > > that points to a stub network. > > OK. I understand this. > > That said, my first reactions would be: > > 1) is this a real deployment scenario? Who is setting up a network > like this? Maybe they shouldn't do this and there are better > approaches... There are a wide variety of use cases; 'draft-rangers-russert' lists many of them. > 2) So what if the default route (on some hosts) points to the wrong > thing, the stub router will presumably send a redirect for any > traffic it is relaying, and the host will update its cache and from > that point forward things are fine. Perhaps not "optimal" in a pure > sense, but I certainly don't see this is as so broken a fix is > needed... At least not without really understanding who is > operating a network like this... I'm afraid I didn't understand this; the hosts will discover default routes in the same way that the stub routers will. ISATAP is an example of a mechanism that provides for hosts to discover the unicast addresses of default routers. Fred [email protected] > Thomas -------------------------------------------------------------------- IETF IPv6 working group mailing list [email protected] Administrative Requests: https://www.ietf.org/mailman/listinfo/ipv6 --------------------------------------------------------------------
