Hi, Fred, Thanks so much for your prompt response. Please find my comments in-line...
On 07/18/2012 10:03 PM, Fred Baker (fred) wrote: >> "A host that receives a first-fragment that fails to include the >> entire IPv6 header chain MUST silently drop the aforementioned >> fragment". >> >> Clearly, since such packets are illegal, they shouldn't exist in >> the first place... so dropping them makes sense. >> >> Thoughts? > > I would say "SHOULD", but I'm OK with the fundamental statement. The > Robustness Principle has some built-in tension: "be liberal in what > you accept and conservative in what you send" often works out to mean > "accept a technically-illegal message if you can work out an > unambiguous intent"; what you are saying is to "be strict in what you > accept", which in this case is (as you suggest) probably the right > thing to do. Agreed. > The distinction between "SHOULD" and "MUST" is a little of a chinese > wall. The rule I use, which is neither specified nor universal, is > that I say something "MUST" be obeyed if failing to obey results in > an identifiable failure I've always used the same rule, but ended up reconsidering it upon suggestion of S. Braden when he noted that, as per RFC2119, a "SHOULD" implies that "there may exist valid reasons in particular circumstances to ignore a particular item, but the full implications must be understood and carefully weighed before choosing a different course." So I guess that, from that perspective, to make it a "SHOULD" (rather than a "MUST") one should be able to come up with a good reason to accept such packets... (I should say that I've authored documents that include SHOULDs/MUSTs with your rationale, rather than the one I've just quoted) > (fragmenting a DNF packet, for example, fails > in that if a recipient of DNF fragments will refuse to reassemble > them, this prevents communication that was intended to be supported, > so a packet marked DNF "MUST" not be fragmented), (Side discussion, but just for the fun of it): Actually, I'd argue that the motivation for "MUST NOT" fragment would probably be that the Identification field is most-likely 0, and the node fragmenting the DNF packet is in no good position of selecting a good Fragment ID. Thanks! Cheers, -- Fernando Gont SI6 Networks e-mail: [email protected] PGP Fingerprint: 6666 31C6 D484 63B2 8FB1 E3C4 AE25 0D55 1D4E 7492 -------------------------------------------------------------------- IETF IPv6 working group mailing list [email protected] Administrative Requests: https://www.ietf.org/mailman/listinfo/ipv6 --------------------------------------------------------------------
