Re: [BEHAVE] How to set the DF and the ID values for IPv4 packets (was Re: Amount of fragmentation resulting from translation

[Fernando Gont <fernando at gont.com.ar>]

Hello, Marcelo,

Comments in-line....

> So, consider that the translator receives an IPv6 packet without a
> fragment header.
> Those packets without the fragment header do not contain any ID value.
> The stateless document
> defines that the ID value is set to 0 and the DF set to 1. That works
> modulo the following black hole situation:

It actually doesn't, even in v4-only scenarios. See Section 3.5.1 of
http://www.cpni.gov.uk/Docs/InternetProtocol.pdf



> packets and set DF to zero. In order to do that, we should generate
> values for the ID field so that they do not clash
> 
> That would require changing the stateless document or if we don't want
> to keep the seq number state in that document, but we consider the
> problem is real and want to solve it int he stateful case, then take a
> different approach in the stateless and the staefull document.

For *this* is scenario (xlat), my recommendation would be a RFC1948-like
scheme:

ID = counter + F()

Where F() is a hash function that takes src IPv4, Dst IPv4, Protocol,
and secret_key as parameters.

Thanks!

Kind regards,
-- 
Fernando Gont
e-mail: fernando at gont.com.ar || fgont at acm.org
PGP Fingerprint: 7809 84F5 322E 45C7 F1C9 3945 96EE A9EF D076 FFF1