Re: [rtcweb] IP handling: Using mDNS names for host candidates

Harald Alvestrand <harald@alvestrand.no> Thu, 14 June 2018 21:15 UTC

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From: Harald Alvestrand <harald@alvestrand.no>
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Date: Thu, 14 Jun 2018 23:15:33 +0200
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Subject: Re: [rtcweb] IP handling: Using mDNS names for host candidates
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I have some worries about this proposal. It seems neat, and solves a
specific problem for a specific use case, but it's not a written-up
proposal, rather a sketch for one - and I'm afraid of devils in the details.

For instance:

- If this technique is used for a computer directly connected to the
Internet, with a public IP address, it won't communicate - unless it is
only used on private addresses - because "uuid.local" doesn't resolve,
whereas a public IP address is globally reachable.

- The above means that the proposal needs a definition of "private
address". Do we mean "private" in the RFC 1918 sense? If so, which IPv6
range is covered by the proposal?

- It will only work if the private address usage is the same scope as
mDNS resolution. On an unmanaged LAN it works, and on a network with
explicit mDNS forwarding it works. But on any other deployment, it
forces traffic to go via public IP addresses learned by STUN.

I think this is worth adding. Perhaps as a new "mode 2m"?

But I'd like a commitment to not adding it until we have a full proposal.

Den 12. juni 2018 02:40, skrev Justin Uberti:
> The Safari team has come up with a clever approach to avoid disclosing
> private IP addresses for host candidates. As discussed in this WebKit
> bug <https://bugs.webkit.org/show_bug.cgi?id=174500>, the technique
> works as follows:
> 
>  1. Register a random UUID-based mDNS name when ICE gathering starts
>  2. Replace the private IP address by a "{UUID}.local" string in each
>     host candidate (and set raddr to 0.0.0.0 for other candidates)
>  3. The other party will do mDNS resolution on any candidate having a
>     .local suffix, similar to how hostnames in candidates are handled in
>     RFC 5245, Section 15.1.
> 
> This technique is relevant to the IP handling document, as it addresses
> one of the lesser problems (private IP disclosure) from the overall
> problem statement. While I don't think this will have a large impact on
> the document, including the default mode selection, incorporating this
> technique would result in some moderate changes:
> 
>   * Section 5.1 would mention concealing private IPs in the default case
>     as an explicit goal.
>   * In Section 6, Mode 2 would change from handling out private IPs to
>     handing out mDNS names.
>   * This document would have to describe the technique or point to
>     another document that describes the technique. mmusic-ice-sip-sdp,
>     Section 4.1
>     <https://tools.ietf.org/html/draft-ietf-mmusic-ice-sip-sdp-20#section-4.1> seems
>     like a good option, as it already covers how to handle DNS names in
>     ICE candidates.
> 
> This is a significant improvement and I think we will want to
> incorporate this suggestion. Is this something we could do as part of
> this WGLC, or should we look for another option?
> 
> 
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