[dhcwg] FW: RFC3315 question
Ralph Droms <rdroms@cisco.com> Fri, 16 February 2007 21:53 UTC
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Date: Fri, 16 Feb 2007 16:53:08 -0500
From: Ralph Droms <rdroms@cisco.com>
To: dhcwg <dhcwg@ietf.org>
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Thread-Topic: RFC3315 question
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Subject: [dhcwg] FW: RFC3315 question
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Alain Durand asked me a couple of questions about the definition of the DUID formats based on link-layer addresses in RFC 3315. The first question is about this text, which appears in both section 9.2, DUID Based on Link-layer Address Plus Time [DUID-LLT], and section 9.4, DUID Based on Link-layer Address [DUID-LL]: The link-layer address is stored in canonical form, as described in RFC 2464. Alain checked RFC 2464, and he can't find how a link layer address is supposed to be stored in canonical form. The closest thing he found is: The Source/Target Link-layer Address option has the following form when the link layer is Ethernet. 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | +- Ethernet -+ | | +- Address -+ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ And, RFC 2464 only describes Ethernet and is silent on other link-layer addresses. There is also an issue with the text: The hardware type MUST be a valid hardware type assigned by the IANA, as described in RFC 826. ...but, RFC 826 makes no reference to IANA. Ted Lemon and I exchanged e-mail about the DUID issue, and I've included Ted's response below. Regarding the IANA/RFC 826 issue, I think it can be addressed by an errata: OLD: The hardware type MUST be a valid hardware type assigned by the IANA as described in RFC 826 [14]. NEW: The hardware type MUST be a valid hardware type from the list of ARP hardware types maintained by IANA at <insert URL here> - Ralph ===== To be honest, I have no idea where the RFC2464 reference came from. I'd never read that RFC, and wasn't even aware of its existence. The word 'canonical' is only used twice in the RFC, and nowhere in the RFC is the meaning of 'canonical' described. The point Alain raises is a really good one, and applies to RFC2464 as well, to some extent - it should define 'canonical'. However, RFC2464 does give us some clue about this in section 2.5.1, Interface Identifiers, on page 8, where it describes in detail how to construct an interface identifier. This does tell us what the author of RFC2464 thought the canonical form is. But Alain's still right that the reference to RFC2464 is a mistake in isolation, because it leaves out all other possible frame header formats. Having said that, the problem remains - without specifying the arrangement of bits, you are left guessing. People seem to have muddled through with RFC2131/2132, and I think they probably will with 3315 as well, but it could have been better specified. I think the correct fix for the RFC2464 problem is to add some text like what's in RFC2373: The details of forming interface identifiers are defined in the appropriate "IPv6 over <link>" specification such as "IPv6 over Ethernet" [ETHER], "IPv6 over FDDI" [FDDI], etc. We'd change it to this: The details of how the link-layer address is formatted are defined in the appropriate "IPv6 over <link>" specification such as "IPv6 over Ethernet" [RFC2464], "IPv6 over FDDI" [RFCnnnn], etc. Specifically, the link-layer address should appear in the DUID-LLT option just as it does in the frame header for that particular link type. For example the link-layer address for an ethernet interface would be formatted in the same way as the Destination Ethernet Address field of the ethernet frame as described in the section of "IPv6 over Ethernet" [RFC2464] titled "Frame Format." This doesn't really solve the problem, because RFC2464 isn't specific about it either, but it gets rid of the erroneous reference to RFC2464 as the _only_ place to go, and it also gives the implementor a valuable clue for how to format the DUID-LLT - look at a frame you captured live on the wire. That way. That's lame, but it's better than nothing. Really, RFC2464 should be more particular about referencing the document (presumably IEEE) that defines the 802.11 header format. You can see that the author had access to that document by reading section 2.5.1, but unfortunately s/he never references it. _______________________________________________ dhcwg mailing list dhcwg@ietf.org https://www1.ietf.org/mailman/listinfo/dhcwg
- [dhcwg] FW: RFC3315 question Ralph Droms
- Re: [dhcwg] FW: RFC3315 question Shane Kerr
- RE: [dhcwg] FW: RFC3315 question Bernie Volz (volz)
- RE: [dhcwg] FW: RFC3315 question Templin, Fred L
- RE: [dhcwg] FW: RFC3315 question Bernie Volz (volz)
- Re: [dhcwg] FW: RFC3315 question Ted Lemon
- RE: [dhcwg] FW: RFC3315 question Bernie Volz (volz)
- Re: [dhcwg] FW: RFC3315 question Ted Lemon
- Re: [dhcwg] FW: RFC3315 question Markus Stenberg
- Re: [dhcwg] FW: RFC3315 question David W. Hankins
- Re: [dhcwg] FW: RFC3315 question Ralph Droms
- RE: [dhcwg] FW: RFC3315 question Bernie Volz (volz)
- Re: [dhcwg] FW: RFC3315 question Ted Lemon