All, I think everyone agrees that intermediate fragmentation (e.g. by routers having high-speed links in the middle of the path) can be problematic,and that is why IPv6 does NOT require that (i.e. RFC-2460 says that the "DF" bit is invisible but always set for IPv6).
That noted, I agree very much with Fernando Gont's comments on 5th July 2013 that IPv6 fragmentation in end systems ought NOT be deprecated -- and I find his reasoning compelling. (SEPARATELY) Not all deployed links are built out of wired/wireless Ethernet or SONET. The assumption that everything is either Ethernet or SONET (or perhaps WDM) is a bit of a "First World" assumption and puts lesser-developed countries/regions at a significant disadvantage for Internet access. Frankly it is embarrassing for IETF participants to make such an assumption (i.e. that all links are Ethernet, SONET, WDM, or better). While it is fine to optimise so that Ethernet or SONET links have great performance, for example by eliminating the requirement for backbone routers to fragment packets, we ought to retain the ancient "IP OVER EVERYTHING" mantra that has served the Internet (and ALL regions of the world) so well for so many years now. I know of a number of link technologies that simply can't support the existing 1280 byte minimum IPv6 MTU. Links with the lower MTU overwhelmingly are relatively low speed wireless links (everything in the gamut from HF radio to SATCOM). My concerns about this have been expressed in IPv6 WG meetings dating back to the early 1990s, as IETF meeting minutes show. All the data available to me indicates that these lower-speed (and smaller MTU) links are NOT going away. For HF radio links, link transmission speed is usually measured in Kbps, with some deployed IPv4/HF links today running as low as 2.4 Kbps. VHF and UHF line-of-sight links tend to be much faster than HF, but are still well below the slowest modern Ethernet link (i.e. 10 Mbps). The IPv6 concept of adding a special link-specific fragmentation/reassembly protocol layer has never been practical. By definition, these links have severe bandwidth limitations already. I've seen multiple instances where specialised routers that are connected to these LOW speed links insert IPv6 Fragmentation Headers and perform intermediate fragmentation to get IPv6 packets through such links. In these special cases, there is no performance issue because these wireless links have such low data rates. A result of deprecating the IPv6 Fragmentation Header will be that such links will be running IPv4 *forever*. This is the opposite of encouraging IPv6 transition -- it is preventing IPv6 transition. It also probably requires the ongoing deployment of IPv6::IPv4 protocol translation gateways -- and also probably inhibits Internet deployment outside of "1st World" countries. Sigh. Deprecating IPv6 Fragmentation Header and related end-system support is going to harm users and inhibit transition to IPv6. PLEASE, PLEASE, let us NOT go there. Sincerely Yours, Ran Atkinson -------------------------------------------------------------------- IETF IPv6 working group mailing list ipv6@ietf.org Administrative Requests: https://www.ietf.org/mailman/listinfo/ipv6 --------------------------------------------------------------------
