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

"Adam Langley" <agl@imperialviolet.org> Wed, 16 July 2008 21:53 UTC

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Date: Wed, 16 Jul 2008 14:54:13 -0700
From: Adam Langley <agl@imperialviolet.org>
To: 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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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]

[1] http://www.freebsd.org/cgi/cvsweb.cgi/~checkout~/src/sys/netinet/tcp_output.c?rev=1.151;content-type=text%2Fplain
  tcp_addoptions function


AGL

-- 
Adam Langley agl@imperialviolet.org http://www.imperialviolet.org
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