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Re: [Int-area] Call for adoption of draft-xu-intarea-ip-in-udp-03

Brian E Carpenter <brian.e.carpenter@gmail.com> Tue, 31 May 2016 20:01 UTC

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To: Xuxiaohu <xuxiaohu@huawei.com>, Joe Touch <touch@isi.edu>
References: <E83B905A-FF6D-4996-B71A-7921DE4B133B@ericsson.com> <BFC09F5C-D6DF-4B6B-AA95-03919B9F09FB@cisco.com> <573E2A0E.1060609@isi.edu> <1FEE3F8F5CCDE64C9A8E8F4AD27C19EE0D54EB60@NKGEML515-MBX.china.huawei.com> <573F453C.5060908@isi.edu> <1FEE3F8F5CCDE64C9A8E8F4AD27C19EE0D554B73@NKGEML515-MBS.china.huawei.com> <5743303C.5040109@isi.edu> <1FEE3F8F5CCDE64C9A8E8F4AD27C19EE0D55514C@NKGEML515-MBS.china.huawei.com> <5743DD16.3050506@isi.edu> <e523724c-cffd-784d-0147-aa64c2787727@bogus.com> <574C8288.7080804@isi.edu> <bd97158e-b6f1-5e55-af9a-07eca2660479@gmail.com> <1FEE3F8F5CCDE64C9A8E8F4AD27C19EE0D55A035@NKGEML515-MBS.china.huawei.com>
From: Brian E Carpenter <brian.e.carpenter@gmail.com>
Organization: University of Auckland
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Date: Wed, 01 Jun 2016 08:01:17 +1200
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Cc: "int-area@ietf.org" <int-area@ietf.org>
Subject: Re: [Int-area] Call for adoption of draft-xu-intarea-ip-in-udp-03
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On 31/05/2016 20:13, Xuxiaohu wrote:
> 
> 
>> -----Original Message-----
>> From: Brian E Carpenter [mailto:brian.e.carpenter@gmail.com]
>> Sent: Tuesday, May 31, 2016 4:46 AM
>> To: Joe Touch
>> Cc: joel jaeggli; Xuxiaohu; Fred Baker (fred); Wassim Haddad; int-area@ietf.org
>> Subject: Re: [Int-area] Call for adoption of draft-xu-intarea-ip-in-udp-03
>>
>> And being pedantic...
>> On 31/05/2016 06:12, Joe Touch wrote:
>>>
>>>
>>> On 5/29/2016 4:23 PM, joel jaeggli wrote:
>>>>>> I.e., you MUST support source fragmentation at the ingress at the
>>>>>> outer
>>>>>> IPv6 layer (because UDP doesn't have support for fragmentation and
>>>>>> reassembly). If you make this requirement, you can handle IPv6 over
>>>>>> the tunnel.
>>>> Yeah I don't support it for this reason. getting IP fragments back
>>>> together in the same place a reassembled is hard is in some cases
>>>> especially when you hash. (see frag drop) given alternatives that
>>>> better address such situations it seems hard to justify.
>>>
>>> If you intend to support recursive IP tunneling* and believe that IP
>>> has a minimum MTU, then you have to accept reassembly.
>>
>> If you intend to support recursive datagram tunneling and believe that any path
>> has a minimum MTU, then you have to accept reassembly.
>>
>> This is physics, and nothing to do with design details.
>>
>> (Something I discovered in about 1983, when implementing OSI/CLNP at CERN
>> over a homebrew network with 128 byte packets.)
> 
> Reassembly on the tunnel egress may be acceptable at that old time. However, due to the considerable improvement in network bandwidth capability, the practice acceptable at the old time may have become outdated today.

I don't understand what network capacity has to do with the physical and mathematical
fact that packets larger than N bytes will not fit into a packet limited to N bytes.
That was true in 1983 and will still be true in 2083.

   Brian

> See the MAP implementation experience shared by Ole recently.
> 
> Xiaohu
> 
>>    Brian
>>
>>>
>>> Joe
>>>
>>> * where "recursive IP tunneling" is IP in [zero or more other
>>> protocols] in IP.
>>>
>>> _______________________________________________
>>> Int-area mailing list
>>> Int-area@ietf.org
>>> https://www.ietf.org/mailman/listinfo/int-area
>>>

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