netdev - RE: tcpdump's capture filter: "vlan" doesn't match

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Date:	Fri, 17 Oct 2014 01:25:17 +0200
From:	Lukas Tribus <luky-37@...mail.com>
To:	Daniel Borkmann <dborkman@...hat.com>
CC:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	John Fastabend <john.r.fastabend@...el.com>,
	Michał Mirosław <mirq-linux@...e.qmqm.pl>,
	Jiri Pirko <jpirko@...hat.com>,
	Ben Hutchings <bhutchings@...arflare.com>,
	Atzm Watanabe <atzm@...atosphere.co.jp>,
	Patrick McHardy <kaber@...sh.net>,
	Jesse Gross <jesse@...ira.com>,
	Michael Richardson <mcr@...delman.ca>,
	Ani Sinha <ani@...stanetworks.com>
Subject: RE: tcpdump's capture filter: "vlan" doesn't match

>> Isn't disabling rx-vlan-offloading supposed to remedy those problems?
>
> There were some discussions on this in the past e.g. [1]. We have
> SKF_AD_VLAN_TAG and SKF_AD_VLAN_TAG_PRESENT for the BPF filter on
> this, but libpcap is currently not making use of any of them.
>
> [1] http://thread.gmane.org/gmane.linux.network/247947

Thanks for the link. I see the situation is unfortunate and although those
new BPF filters in the kernel may fix the actual filtering problem, one
thing seems to remain impossible: disabling all this kernel magic and
passing the frame as-is to libpcap without interception (avoiding any
kind of artificial header reconstruction).

How is the situation with netsniff-ng anyway? Does it use vlan BPF filter
in the kernel?



Regards,

Lukas

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