Re: [tcpm] TCP-AO Option Layout

On Tuesday 29 July 2008, YOSHIFUJI Hideaki / 吉藤英明 wrote:
> > If we want to reduce padding and keep the MAC aligned, the best option
> > is:
> >
> > ~                 +---------+---------+---------+---------+
> > ~                 | Kind=?? | Length  |  KeyID  |   0     |
> > ~                 +---------+---------+---------+---------+
> > ~                 ...
> > ~                 ...
> > ~                 +---------------------------------------+
> > ~                 |       MAC...                          |
> > ~                 +---------------------------------------+
>
> I support this.
>
> > I.e., pad ourselves. We suggest that the option start word-aligned. This
> > wastes space, IMO.
>
> I don't think this is a waste of space and good thing to have -
> to save CPU cycle(s).

Please don't do this. Leave the padding as an issue for the OS implementation 
just like all other TCP options do. Any OS implementation may add a NOP at 
the begging and solve this problem (if it actually exists).

Also, noone can say whether there will be a 5 bytes option in the future that 
will be able to be effectively combined with this one.

Btw, how sure can you be that *all* TCP implementations out there (PCs, 
Non-PCs, small-embedded, mobiles etc) benefit from exactly 32bit writes? 

IMHO, when talking about thinks like this one, the underlying hardware should 
not be considered at all.
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Re: [tcpm] TCP-AO Option Layout - Alignment and Padding