* Fernando Gont: > Hi, Florian, > > On 12/23/2011 07:46 AM, Florian Weimer wrote: >>> That aside, I don't know whether e.g. NAT64 or the like used this >>> (.e.g, whether they are used for transition technologies as envisioned >>> in RFC 2460). However, it might also be the case that such "atomic >>> fragments" are generated when communicating through networks that do >>> not really have a MTU >= 1280. In such scenarios there might be some >>> for of gateway that sends the ICMPv6 PTB advertising a Next-Hop MTU >>> smaller than 1280, thus resulting in atomic fragments (such that it's >>> easier for the "gateway" to fragment the IPv6 packets). >> >> Yes, this seems a plausible explanation. I wouldn't consider this >> actual use, rather network misconfiguration. > > Why?
What Brian said---IPv6 is supposed to have a lower bound on the MTU. I just don't think it's a good idea to through that out of the window because there are genuine advantages. >> In my opinion, we need >> more evidence that these fragments actually serve a useful purpose. >> >>> That aside, there's the proposal by Mark Andrews which would add yet >>> another use case for these atomic fragments. >> >> Not really. It's a workaround so that stateless IPv6 services are >> possible, despite this protocol weiredness. > > Not sure what you mean. Without the API change in draft-andrews-6man-force-fragmentation, it is flat out impossible to server IPv6 traffic in a stateless fashion. The stack is required to keep a per-destination cache which records the necessity of a fragment extension header, even if the application never sends any packets larger than 1280 bytes. > Sorry, I cannot see why some packets would require going through a > translator, while others wouldn't. The joy of packet switching. 8-) > That is, if the intended destination is really a v4 node, all packets > meant to it will go through a translator, If it's not, none will. If the target is a v4 node, surely the network can just fragment as needed, and reassemble using the v4 fragmentation information? That's why I assumed the actual use case has to be more complicated (such as translation back to v6). I'm attempting a reductio ad absurdum here---trying to show that for all potential use cases of atomic fragments, there are much simpler alternatives, and the remaining ones are utterly bizarre and not worth supporting. -- Florian Weimer <fwei...@bfk.de> BFK edv-consulting GmbH http://www.bfk.de/ Kriegsstraße 100 tel: +49-721-96201-1 D-76133 Karlsruhe fax: +49-721-96201-99 -------------------------------------------------------------------- IETF IPv6 working group mailing list ipv6@ietf.org Administrative Requests: https://www.ietf.org/mailman/listinfo/ipv6 --------------------------------------------------------------------
