Re: Last Call: 'Linklocal Multicast Name Resolution (LLMNR)' to Proposed Standard

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Hi Stuart,

Somehow our discussion has gone awry, and I'm not quite sure why, because I am not sure that we fundamentally disagree with each other. At least, I think that we both see some of the same potential problems, even if we disagree about what steps would be appropriate to resolve them.

[Please note: In this note, I will use the term "LLMNR" to refer to the DNSEXT WG draft named draft-ietf-dnsext-mdns-XX.txt, and I will use the term "mDNS" to refer to the de facto standard Apple mDNS protocol.]

Other than a few minor issues that are being dealt with in a -43 update, I don't think that anyone has raised a blocking technical issue with the LLMNR specification during this IETF LC. If you (or anyone else) has intended to raise a blocking technical issue, either with LLMNR itself or with its ability to coexist with mDNS, please make that clearer to me.

I do, of course, see overlapping purpose/applicability for the mDNS and LLMNR mechanisms, and that is a significant source of concern.

In general, I don't personally think that the Internet would be best-served by having two different widely-deployed mechanisms for link local name resolution. I can infer that the DNSEXT WG agrees (or agreed at one time), since they decided that a selection process was necessary rather than just publishing both (or all three) mechanisms. So, I'm not quite sure what to do given that mDNS _is_ widely deployed, and that we are considering the standardization of LLMNR in an Internet where mDNS must considered as part of the existing landscape.

I am somewhat concerned, for example, that someone could implement LLMNR thinking that it is the same thing as mDNS and only later find that the two do not interoperate. Or that some vendors will ship LLMNR while others ship mDNS, so that products from different vendors will not interoperate. Do others have any thoughts on whether the publication of LLMNR is likely to cause confusion along these lines?

On the other hand, the DNSEXT WG has worked for several years to produce the LLMNR specification, and I don't see anything fundamentally wrong with the mechanism that we have produced (people should respond to the IETF LC if they see blocking technical issues). The authors of that specification gave change control to the IETF community, and they have gone through 40+ document iterations, working towards a document that would achieve DNSEXT consensus. That process was not followed for mDNS (because it was not the chosen solution), and we currently only have one document (LLMNR) that has reached IETF WG consensus and has been submitted for standards publication.

It is possible, in an IETF LC, that we could learn that we do not have IETF consensus to publish something that was produced by an IETF WG. That would be an exceptional and unpleasant situation, but I am open to that possibility. In this particular case, though, I see that a few concerns have been raised that were already raised during the WG process, and I do not see an IETF consensus against publishing the LLMNR document that would override the DNSEXT WG consensus to publish it. If folks disagree with this determination, they should speak up, because I am currently of the opinion that we do have DNSEXT WG and IETF consensus to publish LLMNR on the IETF standards track.

Some folks have already implemented LLMNR, and at least one company has shipped it in a commercial product.

So, I think that, no matter what happens, we are stuck in a world where there will be at least two link-local name resolution mechanisms. Having come to that conclusion, I don't believe that there is any perfect answer here. I think that our focus needs to be on minimizing the potential damage or confusion that will be caused by having two mechanisms.

Stuart, have you considered publishing mDNS on the individual submission track (as an Informational RFC)? I think that the existence of that document might help to avoid confusion about whether the LLMNR document describes mDNS.

The LLMNR document already includes an informative reference to draft-cheshire-dnsext-multicastdns-05.txt, but it does so rather obscurely (citing a need to use a TTL of 255 for "compatibility with Apple Bonjour"). It might be better to include a pointer to this document earlier in the LLMNR spec and indicate that Apple Bonjour includes another mechanisms for link-local name resolution. Also, I am surprised by the reference to compatibility with Apple Bonjour (which I didn't notice in my AD review), because I was not under the impression that these protocols are compatible (as in interoperable). LLMNR authors, could you perhaps elaborate on what was meant by this statement?

Would the LLMNR authors and or the DNSEXT WG object to the idea of including an informative reference to mDNS (presumably as "Apple Bonjour") earlier in the document, stating that it is another link-local name resolution protocol and making it clear to what extent LLMNR is (or is not) compatible with mDNS?

Thoughts?
Margaret



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