Hi Richard: One cautionary node: in my mind, secure, yet easy to use device configuration and trust lifecycle management relies on devices to be uniquely identified in a static way, in a vendor independent fashion. As such, this assumes a globally unique name space across all nodes. This suggests that "globally unique" is not a proper adjective for "16-bit addresses" (unless you wish global device deployment to be limited to 64k devices only [which I hope not...]).
Rene == Having globally-unique 16-bit addresses helps with header compression. Typically, all or most of the traffic in a LoWPAN is either to or from one of a small number of nodes. -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Richard Kelsey Sent: Thursday, June 11, 2009 9:03 AM To: Zach Shelby Cc: [email protected] Subject: Re: [6lowpan] ad hoc whiteboard (was: [Fwd: New Version Notification for draft-ietf-6lowpan-nd-03]) Date: Wed, 10 Jun 2009 22:53:17 +0300 From: Zach Shelby <[email protected]> What do others think, is this a concern? Do we just run Ad-hoc LoWPANs with no ER at all by default? If so, what is the simplest way to detect this, and are you happy with how the network will function after this? Zach, I don't think it would make sense to not have an ER in an ad hoc LoWPAN. As you said, some router must generate a ULA prefix and disseminate it, so there should be an ER. I am hoping that we can come up with a way to run large ad hoc networks of (exclusively) small devices without any major perturbations to the protocol. The whiteboard is used for assigning 16-bit addresses and for detecting collisions in OIIs (usually derived from EUI64s). Even with a whiteboard, OII collision detection is somewhat problematic in that there can be a significant delay during which the colliding devices will be using the same address(es). Would it be acceptable for the ER in an ad hoc network to maintain only a partial whiteboard containing some fraction of the networks OIIs? This would increase the delay before an OII conflict was detected, but the network would otherwise behave as if the ER had a full whiteboard. Having globally-unique 16-bit addresses helps with header compression. Typically, all or most of the traffic in a LoWPAN is either to or from one of a small number of nodes. Ideally, in a large ad hoc network of small devices the ER could assign globally-unique 16-bit addresses to only the high-traffic devices (including itself). This could be done by adding a 1-bit flag to address options in order to indicate that the requesting host is a high- traffic device. The flag would be only be set if the A (address generation) flag were also set. A memory-poor ad hoc ER would use the flag in deciding which address generation requests to honor. All other ERs would ignore the flag and always generate an address. In summary, if an ad hoc ER lacks sufficient memory for a full whiteboard, we would see the following: - An increased delay in detecting OII collisions. - Not all requests for address generation would be honored; preference would be given for hosts indicating that they were high traffic devices. - Some loss in header compression for packets to or from hosts that did not receive 16-bit addresses. - Local (one hop) detection and repair of 16-bit addresses at the link layer, presumably done in conjunction with link-layer security. -Richard Kelsey _______________________________________________ 6lowpan mailing list [email protected] https://www.ietf.org/mailman/listinfo/6lowpan _______________________________________________ 6lowpan mailing list [email protected] https://www.ietf.org/mailman/listinfo/6lowpan
