Hi Brian, > -----Original Message----- > From: Brian E Carpenter [mailto:[email protected]] > Sent: Tuesday, December 01, 2009 7:18 PM > To: Templin, Fred L > Cc: Thomas Narten; [email protected] > Subject: Re: New draft on "Stub Router Advertisements in IPv6 > NeighborDiscovery" > > > The NBMA link and all of its attached devices is also > > a separate site, > > Fred, can you explain what NBMA technologies you are thinking > of? I think we successfully proved that ATM is not a viable > access technology precisely because it creates the NBMA problem, > so I'm wondering why we are trying again to solve this problem.
The primary NBMA technology I am thinking of is ISATAP/VET. To Bob's point, though, I am coming around to the point of view that if OSPF or some other IGP can be used then it probably should be used. If it cannot be used for some reason, however, then the alternatives are to fashion either a hub-and-spoke or mesh approach. > As Mark Smith pointed out, the ADSL ISPs have adopted (or rather, > cobbled together) a hub and spoke solution for legacy reasons: > > >> PPPoE makes > >> broadband look like high speed dialup, which allowed ISPs to introduce > >> broadband fairly rapidly without having to change their backend > >> authentication/billing systems etc. > > But at least that solution is clear. ISATAP/VET can do hub-and-spoke by having stub routers discover a well-known set of default routers on the link via the Potential Router List discovery mechanisms. Then, the stub routers can forward everything via a default route even if the default router is only going to hairpin the traffic back into another stub router on the link. ISATAP/VET can do mesh by having the default routers send router-to-router redirects as we have discussed. Then, stub routers can forward traffic directly to one another while eliminating the dogleg. > Incidentally, we have existing terminology for distinguishing a particular > router on a subnet: the 'designated router' in OSPF. As I understand, it's > the only router on the subnet allowed to send Link State Advertisements. > Is your 'authoritative' router comparable to that? In what way does OSPF > not match your problem? What I am calling 'authoritative' router is one and the same with what ISATAP calls a Potential Router List (PRL) router; they can advertise "default" and provide default routing services for forwarding packets off the link. To my understanding, however, the OSPF designated router and backup designated router are not necessarily one and the same as an authoritative/PRL router. For example, I do not think it is necessary for an OSPF router to provide default routing services in order for it to become an OSPF designated router. Fred [email protected] > Brian -------------------------------------------------------------------- IETF IPv6 working group mailing list [email protected] Administrative Requests: https://www.ietf.org/mailman/listinfo/ipv6 --------------------------------------------------------------------
