> -----Original Message----- > From: [email protected] [mailto:[email protected]] On Behalf Of > Brian E Carpenter > Sent: Monday, October 07, 2013 5:18 PM > To: C. M. Heard > Cc: [email protected]; Adrian Farrel; draft-ietf-6man-ext- > [email protected]; [email protected]; The IESG > Subject: Re: Adrian Farrel's No Objection on draft-ietf-6man-ext- > transmit-04: (with COMMENT) > > On 08/10/2013 10:28, C. M. Heard wrote: > ... > > > Maybe I'm making too much of this. Certainly a reasonable action > > for a middlebox that's told to pass packets with extension header > > types 253 and 254 is to stop parsing when it encounters those next > > header types and forward the packet in question. Maybe that's > > obvious to everyone -- but it seems to me that the spec, as written, > > is actually asking for something different. > > There's no header length field in an IPv6 header. That means that > since header types 253 and 254 might be used either for experimental > extension headers or for experimental payload types, there's no > generic way for a middlebox to tell the difference. I think that's > an issue that the current draft cannot resolve. I suspect we probably > need an extra sentence to state the problem, but the authors will > wait for direction on that.
When Wireshark encounters a header type 253 or 254, it assumes it is an unknown extension header of length 8 bytes, then skips ahead and attempts to parse anything that follows as additional headers. Wireshark can be thought of as a middlebox of sorts (albeit one that does not alter the traffic flow), and it wouldn't be hard to imagine real middleboxes that do the same thing when they encounter 253/254. Thanks - Fred [email protected] > Brian > -------------------------------------------------------------------- > 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 --------------------------------------------------------------------
