* Ronald Bonica > [draft-bonica-6man-frag-deprecate]
Being an operator I would definitively welcome getting rid of the complexities dealing with IPv6 fragments bring. That said, the draft needs additional discussion on this could be accomplished without breaking assumptions made by other protocols, though. On my network, I have two legitimate consumers of IPv6 fragments: 1) OSPFv3. RFC 2740 A.1 says «OSPF does not define a way to fragment its protocol packets, and depends on IPv6 fragmentation when transmitting packets larger than the link MTU». It does goes on to say «the OSPF packet types that are likely to be large [...] can usually be split into several separate protocol packets, without loss of functionality. This is recommended; IPv6 fragmentation should be avoided whenever possible». In my experience however, the implementation vendors appears to have skipped over that last recommendation. 2) SIIT (RFC 6145). There are several corner cases where a SIIT translator, or an IPv6 node communicating with an IPv4 node through such a translator, have to deal with IPv6 fragments. In particular: - When a SIIT translator receives an IPv4 packet with DF=0 that would result in an IPv6 packet that would exceed the IPv6 link MTU, it will split the original packet into IPv6 fragments. - When a SIIT translator receives an IPv4 fragment, it will translate this into one or more IPv6 fragments. - When the SIIT translator receives an IPv4 packet with DF=0 it «SHOULD always include an IPv6 Fragment Header to indicate that the sender allows fragmentation». (I wouldn't miss this feature going away though, as I disable it anyway.) - When an IPv6 node receives an ICMPv6 Packet Too Big message indicating a Path MTU less than 1280, it should either 1) simply heed the indicated Path MTU, or 2) limit the size of subsequent transmitted packets to 1280 and include a Fragmentation header (w/MF=0, i.e., an "atomic" fragment) in them. See RFC 2460 section 5. I know that Linux takes this second approach, at least. I cannot support your draft until it discusses or provides solutions for the above considerations. Finally I'll note that in all of the above cases, the use of IPv6 fragments is limited to within a single administrative domain (i.e., my network), so the rationale that IPv6 fragmentation does not work over the Internet does not really apply. Best regards, Tore Anderson -------------------------------------------------------------------- IETF IPv6 working group mailing list [email protected] Administrative Requests: https://www.ietf.org/mailman/listinfo/ipv6 --------------------------------------------------------------------
