Re: [Hipsec] Stephen Farrell's No Objection on draft-ietf-hip-multihoming-11: (with COMMENT)

Stephen Farrell <> Wed, 21 September 2016 07:28 UTC

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To: Tom Henderson <>
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From: Stephen Farrell <>
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Subject: Re: [Hipsec] Stephen Farrell's No Objection on draft-ietf-hip-multihoming-11: (with COMMENT)
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Hi Tom,

On 18/09/16 20:00, Tom Henderson wrote:
> Stephen, thanks for your comments; replies inline below
> On 09/14/2016 04:25 AM, Stephen Farrell wrote:
>> Stephen Farrell has entered the following ballot position for
>> draft-ietf-hip-multihoming-11: No Objection
>> ----------------------------------------------------------------------
>> ----------------------------------------------------------------------
>> - I think section 6 ought note the privacy issue that
>> was relatively recently with WebRTC and ICE where a
>> client might not want all of it's IP addresses
>> exposed, as doing so could expose the fact that the
>> client e.g. is using Tor or another VPN service. The
>> issue being that in some locations, that information
>> may be quite sensitive.  4.2 notes this but in a quite
>> opaque way, ("may be held back") but it'd be better to
>> say some more. 5.1 is also relevant maybe in that it
>> says one "SHOULD avoid" sending info about virtual
>> interfaces. Anyway, I think it'd be good to add some
>> recognition of this privacy issue to section 6. I am
>> not arguing that this draft ought specify the one true
>> way to avoid this problem, but only that it be
>> recognised.
> Your comment led me to review this draft
> which I would be inclined to cite, but I am not sure whether it will be put forward for publication soon (and therefore am not sure about citing it).
> The below might make a possible summary paragraph to add, however:
> "The exposure of all of a host's IP addresses through HIP
>  multihoming extensions may raise privacy concerns.  A host
>  may be trying to hide its location in some contexts through
>  the use of a VPN or other virtual interfaces.  Similar
>  privacy issues also arise in other frameworks such as WebRTC
>  and are not specific to HIP.  Implementations SHOULD provide
>  a mechanism to allow the host administrator to block the 
>  exposure of selected addresses or address ranges."

Looks good to me, thanks.

>> - 4.11: what's the concern about anti-replay windows?
>> I didn't get that fwiw, not sure if that just my
>> relative ignorance of HIP or if more needs to be said
>> in the document.
> It is explained in this sentence:
>   "However, the use of different source
>    and destination addresses typically leads to different paths, with
>    different latencies in the network, and if packets were to arrive via
>    an arbitrary destination IP address (or path) for a given SPI, the
>    reordering due to different latencies may cause some packets to fall
>    outside of the ESP anti-replay window."

Really? I'm surprised that that's at all likely. What size of
window do folks tend to use? It must be small if path diversity
has that effect. (Note: I'm not asking for a change to the text
just wondering about it/educating myself:-)


> Can you suggest changes or do you have a concern with what is stated?
> - Tom