From: David Miller <davem@redhat.com>
To: v4l@stuffedcow.net
Cc: netdev@vger.kernel.org
Subject: Re: ppp_generic: fix multilink fragment MTU calculation (again)
Date: Tue, 20 Sep 2011 15:21:28 -0400 (EDT) [thread overview]
Message-ID: <20110920.152128.1875285861948423018.davem@redhat.com> (raw)
In-Reply-To: <4E7681BD.2040902@stuffedcow.net>
From: Henry Wong <v4l@stuffedcow.net>
Date: Sun, 18 Sep 2011 19:41:49 -0400
> When using MLPPP, the maximum size of a fragment is incorrectly
> calculated with an offset of -2.
> This patch reverses the changes in the patch found here:
> http://marc.info/?l=linux-netdev&m=123541324010539&w=2
>
> The value of hdrlen includes the size of both the 2-byte PPP protocol
> field and the 2- or 4-byte multilink header (2+4=6 for long sequence
> numbers, 2+2=4 for short sequence numbers). Section 2 of RFC1661 says
> that the MRU that is negotiated (i.e., the MTU of the sending system)
> includes only the PPP payload but not the protocol field, thus the
> correct MTU should be the link's MTU minus the multilink header (mtu -
> (hdrlen-2)).
>
> The incorrect calculation causes Linux to fragment packets to a size
> two bytes smaller than the allowed MTU. While not technically illegal,
> this behaviour confounds MRU-tuning to avoid PPP-layer fragmentation.
>
> Signed-off-by: Henry Wong <henry@stuffedcow.net>
Applied, thanks.
There were several cases of trailing whitespace in your patch which I
needed to fix up. Please don't be so careless in the future.
Thanks.
next prev parent reply other threads:[~2011-09-20 19:21 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-09-18 23:41 ppp_generic: fix multilink fragment MTU calculation (again) Henry Wong
2011-09-20 19:21 ` David Miller [this message]
2011-09-20 19:54 ` Henry Wong
2011-09-20 20:01 ` David Miller
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