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

Miika Komu <mkomu@cs.hut.fi> Mon, 18 October 2010 06:35 UTC

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Date: Mon, 18 Oct 2010 09:39:04 +0300
From: Miika Komu <mkomu@cs.hut.fi>
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To: Shinta Sugimoto <shinta@sfc.wide.ad.jp>
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Cc: shim6@ietf.org
Subject: Re: [shim6] AD review of draft-ietf-shim6-multihome-shim-api
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Hi Shinta,

On 16/10/10 18:01, Shinta Sugimoto wrote:
> Hi Miika,
>
> (10/10/16 19:47), Miika Komu wrote:
>
> (snip)
>
>>> What about updating the texts for Section 13.1.2 (replacing the second
>>> paragraph) as follows:
>>>
>>> If the shim sub-layer turns out to be HIP, the HIP implementation MUST
>>> reject the request (SHIM_LOC_PEER_SEND as cmsg_type) for using a unknown
>>> destination locator. There is, however, an exceptional case where the
>>> HIP implementation SHOULD accept the request provided that the message
>>> to be sent by sendmsg() contains an I1 packet. In this exceptional case,
>>> the kernel SHOULD accept the request even if there is no shim context
>>> associated with the socket.
>>>
>>> Does this sound reasonable?
>>
>> It does, except why do we need to restrict to sendmsg()?
>
> Because it is possible to distinguish the exceptional case from the
> normal case. Suppose you allow it by setsockopt(). How do you
> distinguish the two cases? I have no idea how to do it.

can you remind why it needs to be distinguished? If there's no reason, 
what about:

There is, however, an exceptional case where the HIP layer SHOULD accept 
the request. The case occurs when there is no context or the HIP state 
machine is in UNASSOCIATED state. In this exceptional case,
the socket layer SHOULD accept the request.

>> I would also
>> suggest the following changes:
>>
>> * s/implementation/layer/
>> * s/kernel/HIP layer/
>
> OK.
>
>> * s/constains an I1 packet/would be used to initiate a key exchange by
>> the HIP layer/
>
> Let me clarify. Do you foresee other data than I1 packet which would
> trigger the HIP key exchange? I thought it is the HIP daemon who uses
> the ancillary data (SHIM_LOC_PEER_SEND as cmsg_type) to send the I1
> packet to a designated locator. Or, is it the application that uses the
> socket option to send user data to a designated locator? If so, how can
> the kernel distinguish the exceptional case from the normal case? Note
> that the suggested text is saying that normally the kernel must reject
> the request if there is no shim context associated with the socket.

Please note that I1 in this context is misleading because it sounds like 
the application is sending the I1 (where as it should hipd sending it).

There's actually a case where there's no need to send I1:

https://tools.ietf.org/html/draft-ietf-hip-hiccups-05

I believe the suggested text above should cover it too, but we shouldn't 
be too specific about it because it's functionality uncommon between 
SHIM6 and HIP.