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Date:	Thu, 24 Mar 2016 16:56:03 -0700
From:	Cong Wang <>
To:	Ben Greear <>
Cc:	netdev <>, Evan Jones <>,
	Vijay P <>, Cong Wang <>
Subject: Re: veth regression with "don’t modify ip_summed; doing so treats packets with bad checksums as good."

On Thu, Mar 24, 2016 at 3:01 PM, Ben Greear <> wrote:
> I have an application that creates two pairs of veth devices.
> a <-> b       c <-> d
> b and c have a raw packet socket opened on them and I 'bridge' frames
> between b and c to provide network emulation (ie, configurable delay).

IIUC, you create two raw sockets in order to bridge these two veth pairs?
That is, to receive packets on one socket and deliver packets on the other?

> I put IP on a, on d, and then create a UDP connection
> (using policy based routing to ensure frames are sent on the appropriate
> interfaces).
> This is user-space only app, and kernel in this case is completely
> unmodified.
> The commit below breaks this feature:  UDP frames are sniffed on both a and
> d ports
> (in both directions), but the UDP socket does not receive frames.
> Using normal ethernet ports, this network emulation feature works fine, so
> it is
> specific to VETH.
> A similar test with just sending UDP between a single veth pair:  e <-> f
> works fine.  Maybe it has something to do with raw packets?

Yeah, I have the same feeling. Could you trace kfree_skb() to see
where these packets are dropped? At UDP layer?


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