Re: [Anima-bootstrap] bootstrap over CoAP

"Max Pritikin (pritikin)" <pritikin@cisco.com> Sun, 17 July 2016 10:19 UTC

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From: "Max Pritikin (pritikin)" <pritikin@cisco.com>
To: Brian E Carpenter <brian.e.carpenter@gmail.com>
Thread-Topic: [Anima-bootstrap] bootstrap over CoAP
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Date: Sun, 17 Jul 2016 10:19:48 +0000
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References: <3A2F4C70-4960-4592-9314-6EC53B53CC94@cisco.com> <5d5623cd-fe4b-e443-da5d-6a43ffb9b5c6@gmail.com> <57810029.2070408@tzi.org> <17d1c08e-e9c6-d017-58ba-85989d56273d@gmail.com> <5781531A.1080702@tzi.org> <729980b6-767a-b675-1874-5c8e1fefd025@gmail.com> <8D35379D-678D-4293-93E4-150253AE46CE@cisco.com>
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Cc: Carsten Bormann <cabo@tzi.org>, "anima-bootstrap@ietf.org" <anima-bootstrap@ietf.org>, "Panos Kampanakis \(pkampana\)" <pkampana@cisco.com>
Subject: Re: [Anima-bootstrap] bootstrap over CoAP
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> On Jul 10, 2016, at 7:14 PM, Max Pritikin (pritikin) <pritikin@cisco.com> wrote:
> 
>> 
>> On Jul 9, 2016, at 11:33 PM, Brian E Carpenter <brian.e.carpenter@gmail.com> wrote:
>> 
>> On 10/07/2016 07:40, Carsten Bormann wrote:
>>>>> I'm not sure I understood that part of the draft*), but generally CoAP
>>>>> is designed so you can avoid fragmentation 
>>>> 
>>>> That isn't what the draft seems to say, though. However, it's clearly talking
>>>> about application-layer fragmentation to avoid IP fragmentation.
>>> 
>>> (that's segmentation...  I know.)
>>> 
>>>>> (and use the segmentation
>>>>> provided by draft-ietf-core-block instead); the latter has per-segment
>>>>> reliability (acknowledgements and retransmits).   DTLS may require
>>>>> fragmentation during its handshake; this is mitigated if you can use a
>>>>> PSK (symmetric) or, if you need asymmetric, ECC-based ciphersuite, which
>>>>> allows the packets to stay well below 1280 bytes.
>>>> 
>>>> Right. So the app layer chops the message into <1280 byte pieces, and one
>>>> of them is lost...?
>>> 
>>> Each of those segments ("blocks") is (actually, can be, but you do want
>>> to do this with the block-wise protocol) transmitted reliably, so it
>>> doesn't get lost.
>> 
>> OK, so I think that a couple of sentences in draft-pritikin-coap-bootstrap
>> could clarify all that.
> 
> Thank you. We can make that happen,

The relevant text appears to be that CoAP [RFC7252] s4.2 Confirmable and non-Confirmable messages. Draft-ietf-core-block references this in s1 "using Non-confirmable requests within block-wise transfers outside the use case of 
Section 2.8 would escalate the overall non-delivery probability”. Effectively CoAP, and then core-block, address this issue so we don’t need to say anything additional. We could mandate ‘Confirmable’ more so than is indicated in core-block. 

- max

> 
> - max
> 
> 
>> 
>> Thanks
>>   Brian
>> 
>>> Grüße, Carsten
> 
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