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Re: [tcpm] I-D Action:draft-ietf-tcpm-tcp-auth-opt-01.txt

Joe Touch <touch@ISI.EDU> Wed, 16 July 2008 22:38 UTC

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Date: Wed, 16 Jul 2008 15:38:17 -0700
From: Joe Touch <touch@ISI.EDU>
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Subject: Re: [tcpm] I-D Action:draft-ietf-tcpm-tcp-auth-opt-01.txt
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Adam Langley wrote:
> On Wed, Jul 16, 2008 at 2:13 PM, Joe Touch <touch@isi.edu> wrote:
>> This presumes that we misalign the option to start, using the NOP. I would
>> prefer to assume that the option starts word-aligned. I don't see a way to
>> do that, though, without wasting another byte in the option. The goal is
>> currently to assume a half-word aligned start, and let the next option
>> decide whether to pad or not. At that point, it's better to leave the MAC
>> half-word aligned too.
> 
> Just as a couple of data points:
>   * Linux writes options in 32-bit chunks and pads with NOPs before
> the option to make the option a multiple of 4 bytes long
>   * FreeBSD appears to pad with NOPs before the option too[1]

Both of these seem strange. They end up making the end of the option 
align, but disturb the front of the option. Why don't they pad at the end?

(TCP requires only that the last option have that pad, too)

Joe


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