From: Daniel Borkmann <dborkman@redhat.com>
To: Lukas Tribus <luky-37@hotmail.com>
Cc: "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
"John Fastabend" <john.r.fastabend@intel.com>,
"Michał Mirosław" <mirq-linux@rere.qmqm.pl>,
"Jiri Pirko" <jpirko@redhat.com>,
"Ben Hutchings" <bhutchings@solarflare.com>,
"Atzm Watanabe" <atzm@stratosphere.co.jp>,
"Patrick McHardy" <kaber@trash.net>,
"Jesse Gross" <jesse@nicira.com>,
"Michael Richardson" <mcr@sandelman.ca>,
"Ani Sinha" <ani@aristanetworks.com>
Subject: Re: tcpdump's capture filter: "vlan" doesn't match
Date: Fri, 17 Oct 2014 17:48:50 +0200 [thread overview]
Message-ID: <54413A62.9060806@redhat.com> (raw)
In-Reply-To: <DUB123-W25C5DA9BEDC92CD2524B68EDAB0@phx.gbl>
On 10/17/2014 01:25 AM, Lukas Tribus wrote:
>>> 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?
So in netsniff-ng we don't do obscure header reconstruction as it
hurts performance and it can result in incorrect reconstruction cases.
You however can define a bpf_asm program (e.g. tools/net/ in kernel
tree) and use instruction overloading for the vlan case from there.
Thus, you're not tied to the libpcap compiler which misses this.
For more details, I refer you to Documentation/networking/filter.txt .
prev parent reply other threads:[~2014-10-17 15:49 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-10-15 22:58 tcpdump's capture filter: "vlan" doesn't match Lukas Tribus
2014-10-16 6:10 ` Daniel Borkmann
2014-10-16 23:25 ` Lukas Tribus
2014-10-16 23:39 ` Ani Sinha
2014-10-17 15:48 ` Daniel Borkmann [this message]
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