From: Ben Hutchings <bhutchings@solarflare.com>
To: Shan Wei <shanwei@cn.fujitsu.com>
Cc: Herbert Xu <herbert@gondor.apana.org.au>,
netdev <netdev@vger.kernel.org>
Subject: Re: question about UFO behavior for bridge device
Date: Fri, 13 May 2011 14:06:52 +0100 [thread overview]
Message-ID: <1305292012.4065.441.camel@localhost> (raw)
In-Reply-To: <4DCCF803.5020805@cn.fujitsu.com>
On Fri, 2011-05-13 at 17:21 +0800, Shan Wei wrote:
> UDP protocol creates a big packet(skb) in which the data length is greater than MTU.
>
> If device(eth0, lo) does not supports UFO, This big skb will be fragmented to
> many fragments in IP protocol, and fragments are sent one by one by device.
>
> But, if device(eth0, lo) supports UFO, IP protocol don't fragment it, and
> device directly sends it out.
>
> For bridge device which enable UFO, and Ethernet device(eth0) which not
> support UFO, IP protocol also doesn't fragment it, and bridge forwards original
> skb to eth0. For this UFO disabled eth0, kernel needs to perform segmentation
> on so big skb in dev_gso_segment(), and link segmented skbs to next field
> of original skb. Then device sends segmented skbs out, but not original skb.
Right, it does that just before calling the driver's ndo_start_xmit().
> But, actually, i saw original big skb in eth0's tcpdump file, but not segmented skbs.
> The behavior is right or what we want?
> Is there anything missed about my analysis?
I assume that packet capturing is handled earlier in the transmit path.
Ben.
--
Ben Hutchings, Senior Software Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.
next prev parent reply other threads:[~2011-05-13 13:06 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-05-13 9:21 question about UFO behavior for bridge device Shan Wei
2011-05-13 13:06 ` Ben Hutchings [this message]
2011-05-13 14:36 ` Herbert Xu
2011-05-14 9:54 ` Shan Wei
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