* Erik Nordmark: > The motivation for the fragment header insertion was to be able to > support stateless IPv6->IPv4 translators (with multi-path routing), > such as RFC 2765. > > Such a translator normally sets DF (don't fragment) in the IPv4 > packets. But should the IPv4 path MTU drop below 1300 (meaning that a > translated 1280 byte IPv6 packet wouldn't fit),
Stateless gateways cannot perform path MTU discovery, so they don't know about path MTU, and need to send packets with DF=0. > then DF can't be set. In that case a unique IP ID field is needed. The > fragment header contains a unique ID which will be used by the > translator. Why wouldn't the translator be able to pull a random ID out of thin air? How would it generate a unique 16 bit IP ID field from a unique 32 bit IP ID field? It can't just discard the upper 16 bits and pretend that they aren't required to ensure uniqueness. -- 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 --------------------------------------------------------------------
