Re: [shim6] AD review of draft-ietf-shim6-multihome-shim-api

Shinta Sugimoto <shinta@sfc.wide.ad.jp> Thu, 14 October 2010 03:06 UTC

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From: Shinta Sugimoto <shinta@sfc.wide.ad.jp>
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To: "Henderson, Thomas R" <thomas.r.henderson@boeing.com>
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Cc: 'Miika Komu' <mkomu@cs.hut.fi>, shim6 <shim6@ietf.org>, "kristian.slavov@ericsson.com" <kristian.slavov@ericsson.com>
Subject: Re: [shim6] AD review of draft-ietf-shim6-multihome-shim-api
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Hi Thomas,

Henderson, Thomas R wrote:
> 

(snip)

>> For the above reason, I think that we cannot use SHIM_LOC_LOCAL_SEND
>> socket option (or ancillary data) for the purpose of specifying the
>> initial peer locator for the HIP case.
>>
>> If there is a need for application to specify the initial locator, it
>> should be a defined separately, I think. And that is HIP
>> specific. The
>> scope of this document is to define a *common* set of API
>> required for
>> HIP and SHIM6, so I think it's outside the scope of this
>> document. Comments?
> 
> My sense is that it would be OK to proceed in that manner but that
> we probably need to take a pass through this document and the
> HIP API document to make sure that the scope and relationship
> between the documents is clearer.

OK.

> An analogous situation is present in normal sockets in which
> the common socket API has different semantics when the underlying
> transport is datagram or stream.  In that case, there is a family
> of functions (e.g. getprotoent) that can report to the client
> what type of socket it is.  I am wondering whether SHIM_ASSOCIATED
> should be expanded along those lines to tell the client what
> underlying shim type is present (or whether the rules for
> shim context apply or not).

It depends on value that application could get by knowing the type of 
multihoming shim sub-layer (i.e., HIP or SHIM6). I personally cannot 
come up with good usecases.

> 
>>>> Regarding to the case two, it is true that RFC5206
>> basically assumes
>>>> that the peer has to announce it's locator set before the
>>>> local host can
>>>> use them. I believe the peer can refuse to answer if the local host
>>>> triggers a return routability check to an unannounced
>> locator of the
>>>> peer. However, the situation may be changing in RFC5206-bis
>>>> due to the
>>>> recent advancements in IPv4-IPv6 handovers [1] which are not yet
>>>> included in RFC5206.
>>>>
>>>> Tom, care to comment if I am too proactive here?
>>>>
>>>> [1] Secure and efficient IPv4/IPv6 handovers using host-based
>>>> identifier-locator Split, Samu Varjonen et al, 2009
>>> The paper does point out a use case for sending data to a
>> previously unknown locator-- however, it seems to be slightly
>> different than the use case here.  In the paper, the node
>> learns of the address change and it seems that the HIP daemon
>> sends an Echo request-- I take this to mean that the HIP
>> daemon does this proactively.  Here, we are talking about
>> applications triggering this directly and using this API to
>> do so since they may have learned of the address out of band?
>>
>> I wonder how the kernel does not know about the peer locator (IP
>> address) but the application does. You mentioned that
>> application could
>> know the address out-of-band, but how? Do you have good examples?
> 
> I don't have any concrete examples since I don't know of
> any (presently) shim-aware applications, but it is not hard
> to conceive of one in which well-known IP/HIT bindings are
> added to an application configuration file for bootstrapping
> purposes.

OK, I see. Thanks for the clarifications.

Regards,
Shinta