Messages in this thread | | | Date | Wed, 20 Jan 2010 12:59:16 -0000 | Subject | Re: [PATCH] xt_TCPMSS: SYN packets are allowed to contain data | From | "Simon Arlott" <> |
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On Tue, January 19, 2010 15:44, William Allen Simpson wrote: > Simon Arlott wrote: >> On Tue, January 19, 2010 09:17, William Allen Simpson wrote: >> I could change the comment too, but the same logic applies when >> there is data and no MSS option - the packet can't be increased >> in size if it would then exceed 576 bytes and/or the destination >> MTU. >> > Please change the comment.
I've made a new version of the patch which I'll be able to test tonight.
> If there is no MSS option, it should *not* be added, under *ANY* > circumstances. That violates the end-to-end arguments (some call > them principles).
Agreed. The added MSS is likely to be larger than 536 too... I've removed this code.
> MSS isn't about the _destination_ MTU, it's about the *source*. > If you cannot guarantee you know the source MTU, there's no basis > for deciding the MSS.
I was referring to the SYN packet itself. It wouldn't always be possible to add an option without exceeding the MTU of that packet's destination if it had data.
On 19/01/10 12:53, Patrick McHardy wrote: > Simon Arlott wrote: >> If this is 20 (IPv4 Header) + 20 (TCP Header) = 40 bytes, then >> there is no data and the header offset is wrong so it hasn't been >> checked. > > That's odd. If the packet is really only 40 bytes large, then there > are no TCP options, so your patch shouldn't have any effect.
Except to remove the printk which fills up my serial console (because the header offset is wrong).
-- Simon Arlott
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