----- Original Message ----- From: "Doug Barton" <[email protected]> To: <[email protected]> Sent: Thursday, June 13, 2013 9:23 PM > On 06/13/2013 01:17 AM, Randy Bush wrote: > >> FWIW, I don't think anyone has proposed "if the chain is larger than X, > >> then drop". > > > > i am saying that i am telling my neighbor that, if the header length is > > larger than X, it is likely that their packet will not propagate. it's > > an ops bcp statement, not a statement of ipv6 protocol definition. > > > > same as telling them that a bgp announcement of a prefix longer than a > > /24 likely will not propagete. > > > > today, real routers really do drop packets with headers longer than > > various limits. as an op, i am trying to remove the surprise in the > > 'various'. > > I agree with Randy, providing guidance on this topic will be very > helpful, and BCP is the right category. > > As for what the number should be, if 256 is in the 80th percentile or > higher of Warren's survey, that should be fine. A few vendors who are > examining less than that now may be encouraged to increase up to 256 > knowing that they have a reasonable upper bound to shoot for, as opposed > to an arbitrarily large number that varies from implementation to > implementation.
I would like to check with current hardware designers that 256 is a good number for them, as opposed to 240, say. What I mean is that 256 is a nice round number, for us as for them, and so is a natural choice. But sometimes that has to include red tape, control information and such like, so what you get as a nice round number is a bit less when you pass it on to the next level of processing. Of course, with some hardware, that is built in, so that the hardware gets something greater and passes on a nice round number to its user (as with memory cards) but I have known occasions in the past when this was not the case and the choice of a nice round number caused problems. Apart from that 'detail', I agree with the approach. Tom Petch > Doug > > -------------------------------------------------------------------- > IETF IPv6 working group mailing list > [email protected] > Administrative Requests: https://www.ietf.org/mailman/listinfo/ipv6 > -------------------------------------------------------------------- > -------------------------------------------------------------------- IETF IPv6 working group mailing list [email protected] Administrative Requests: https://www.ietf.org/mailman/listinfo/ipv6 --------------------------------------------------------------------
