Re: [shim6] How long is a shim6 header?
Brian E Carpenter <brian.e.carpenter@gmail.com> Mon, 04 November 2013 17:19 UTC
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Date: Tue, 05 Nov 2013 06:10:53 +1300
From: Brian E Carpenter <brian.e.carpenter@gmail.com>
Organization: University of Auckland
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To: Erik Nordmark <nordmark@sonic.net>
References: <52700435.6030606@gmail.com> <5270BB1D.6000004@uclouvain.be> <5274B62E.2090607@yahoo.fr> <52750E8A.90806@gmail.com> <5277CF2B.50701@sonic.net>
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Cc: shim6@ietf.org
Subject: Re: [shim6] How long is a shim6 header?
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On 05/11/2013 05:45, Erik Nordmark wrote: > > Brian, > > It isn't clear to me whether you are talking about the datapath case > (where the shim6 header is followed by a ULP header and payload like > TCP) or a control/signalling case, which has NO_NXT_HEADER. > > In the datapath case the header is exactly 8 bytes. > In the NO_NXT_HEADER things are variable length - but that isn't a > concern for wirewalls since there is no next header to inspect. That's an interesting point. I actually wonder how existing firewalls respond to NO_NXT_HEADER. I think the answer may be disturbing. The problem with most current firewalls is that they drop packets with a shim6 header anyway. Thanks Brian > > Regards, > Erik > > On 11/2/13 7:39 AM, Brian E Carpenter wrote: >> Sure, I agree about 8 minimum: my suggestion was that 40 was a typical >> *large* header. >> >> 1280 would be a complete disaster since firewalls will *never* be able >> to deal with that at line speed. Please read >> draft-wkumari-long-headers-02 >> to understand the concern. We missed this issue during the shim6 design, >> I think. >> >> Regards >> Brian >> >> On 02/11/2013 21:22, Sébastien Barré wrote: >>> Hi, >>> >>> the biggest extension headers are found in signalling packets, in >>> particular those that carry locator information. >>> Since any number of locators can be advertised to the peer, the Shim6 >>> signalling packet may grow up to 1280 bytes, the maximum allowed for >>> shim6 (ref: rfc5533, section 5.1), including >>> the IPv6 header. This leaves up to 1240 bytes for the Shim6 header. >>> >>> Now, this is for signalling. If you worry about payload packets only, >>> then the Shim6 header is either simply absent (when ULIDs are used, the >>> shim6 context at the receiver is looked up based on them), or it >>> contains only a context tag and its size is then 8 bytes. (rfc5533, >>> section 5.2) >>> >>> So, unless I miss something, the Shim6 minimum header size is 8 bytes, >>> not 40. >>> >>> Hope this helps, >>> >>> Sébastien. >>>> >>>> -------- Original Message -------- >>>> Subject: [shim6] How long is a shim6 header? >>>> Date: Wed, 30 Oct 2013 07:53:41 +1300 >>>> From: Brian E Carpenter <brian.e.carpenter@gmail.com> >>>> Organisation: University of Auckland >>>> To: shim6-wg <shim6@ietf.org> >>>> >>>> Hi, >>>> >>>> Does anyone have a quick answer to this question: how big is the >>>> biggest SHIM6 extension header that is likely to occur in practice? >>>> >>>> As far as I can see, it's at least 40 bytes. >>>> >>>> The context for this question is draft-wkumari-long-headers. >>>> >>>> Regards >>>> Brian Carpenter >>>> >>>> _______________________________________________ >>>> shim6 mailing list >>>> shim6@ietf.org >>>> https://www.ietf.org/mailman/listinfo/shim6 >>>> >>>> >>>> >>> >>> >> >> _______________________________________________ >> shim6 mailing list >> shim6@ietf.org >> https://www.ietf.org/mailman/listinfo/shim6 >> > >
- [shim6] How long is a shim6 header? Brian E Carpenter
- Re: [shim6] How long is a shim6 header? Brian E Carpenter
- Re: [shim6] How long is a shim6 header? Brian E Carpenter