netdev - Re: set vlan CFI and TPID

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Date:	Mon, 13 Dec 2010 01:16:37 -0800
From:	Jesse Gross <jesse@...ira.com>
To:	hong zhiyi <zhiyi.hong@...il.com>
Cc:	netdev@...r.kernel.org
Subject: Re: set vlan CFI and TPID

On Sun, Dec 12, 2010 at 6:20 PM, hong zhiyi <zhiyi.hong@...il.com> wrote:
> On Mon, Dec 13, 2010 at 8:20 AM, Jesse Gross <jesse@...ira.com> wrote:
>> On Tue, Dec 7, 2010 at 8:04 PM, hong zhiyi <zhiyi.hong@...il.com> wrote:
>>> Hi All,
>>>
>>> May I ask how to set the 1 bit CFI and 2 bytesTPID in the VLAN header
>>> by vconfig?
>>
>> You can't change them using vconfig.  For 802.1q/Ethernet, the TPID is
>> 0x8100 and the CFI is 0.
>>
>>> and what is the meaning of the egress map and ingress map?
>>
>> These convert between the PCP bits found in the vlan header and the
>> priority field that is used internally for QoS, which you access
>> through tc.
>>
>
> Hi Jesse,
>
> Thank you for your reply.
>
> Then how can it set the value of the TPID and the CFI? Also, I do not
> understand you mentioned the *tc* means, what is the tc?

You can't really.  Like I said, the values are fixed by the standard
for basic 802.1q, which is what Linux implements.  You could, of
course, directly send/receive packets through a raw socket with
whatever values you like.  However, other components of the kernel
that deal with vlans won't recognize them.

tc is a userspace program that (among other things) handles QoS
settings.  Google should be able to turn up information on how to use
it.
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