Hi James; As Ralph indicates, RFC4944 describes a L2.5 fragmentation mechanism and recommends a MTU of 1280 on 802.15.4 links.
That fragmentation mechanism does not allow forwarding at L3 (each L3 hop needs to reassemble). It is also sensitive to frame loss, which sadly is frequent in 802.15.4 though it was mitigated in some environment such as industrial (see WiHART, ISA100.11a, 802.15.4e). Both issues (loss and forwarding) are addressed in http://tools.ietf.org/html/draft-thubert-6lowpan-simple-fragment-recover y but the draft is homeless at the moment. 4944 is also partially obsoleted by RFC-to-be 6282 for the header compression piece. Finally, I'd recommend to take a look at http://tools.ietf.org/html/draft-thubert-6lowpan-backbone-router-02. This work was initially a component of the registration based ND that was designed at 6LoWPAN, and was split in midflight. You'll see in the overview that the concept is to use a backbone router that proxies ND between the 802.15.4 meshes and a higher speed Ethernet (or emulated Ethernet such as WIFI infra mode), with the assumption that the backbone runs classical ND whereas the meshes use the registration-based ND. Cheers, Pascal > -----Original Message----- > From: [email protected] [mailto:[email protected]] On > Behalf Of Ralph Droms (rdroms) > Sent: Wednesday, August 03, 2011 8:12 PM > To: james woodyatt > Cc: Joel Jaeggli; IPv6 Operations; [email protected] > Subject: Re: [homenet] [v6ops] default LAN routing protocol for IPv6CE > router > > RFC 4944 > > - Ralph > > On Aug 3, 2011, at 2:09 PM 8/3/11, james woodyatt wrote: > > > On Aug 3, 2011, at 10:00 , Joel Jaeggli wrote: > >> > >> got a better idea for interconnecting 802.15.4 and 802.3 networks than at > layer-3? > > > > How does 802.15.4 achieve the 1280 octet minimum MTU size required by > IPv6? I'm sure this is explained in an RFC somewhere, but I don't know. > Hoping someone knows off the top of their head and can quickly rattle off a > citation from memory. > > > > > > -- > > james woodyatt <[email protected]> > > member of technical staff, core os networking > > > > > > > > _______________________________________________ > > v6ops mailing list > > [email protected] > > https://www.ietf.org/mailman/listinfo/v6ops > > _______________________________________________ > homenet mailing list > [email protected] > https://www.ietf.org/mailman/listinfo/homenet _______________________________________________ homenet mailing list [email protected] https://www.ietf.org/mailman/listinfo/homenet
