ng_patch and 802.11Q

[Bear]

Hi all,
I did a test, it seems ng_ether will capture after removing VLAN tag?
 > sudo nghook -a em0: lower
 > 0000:  xx xx xx xx xx xx yy yy yy yy yy yy 08 00 45 00  .9D...........E.

em0 is the parent interface of all VLAN, and data sent from this 
interface is ALWAYS tagged.

If I run tcpdump:
 > tcpdump -i em0 -e -n -vv
 >    142.162.175.108.12401 > xxx.xxx.xxx.xxx.14875: [udp sum ok] UDP, 
length 59
 > 09:43:04.576023 xx:xx:xx:xx:xx:xx > yy:yy:yy:yy:yy:yy, ethertype 
802.1Q (0x8100), length 58: vlan 35, p 0, ethertype IPv4, (tos 0x0, ttl 
126, id 5184, offset 0, flags [DF], proto TCP (6), length 40)

I can see the packet has VLAN tag.

How can I obtain raw Ethernet frame with 802.1Q header by netgraph? If I 
cannot get this, it will become impossible to modify the VLAN priority 
field. :-(


On 2013/11/9 11:09 AM, rozhuk.im at gmail.com wrote:
> http://www.netlab.linkpc.net/download/software/FreeBSD/mcastbridge/mcastbr2.
> sh
> http://www.netlab.linkpc.net/forum/index.php?topic=796.0
>
>
>> It seems a good idea... Do you have some example working on ng_ether?
>> The manpage of ng_ether seems no example...
>>
>> On 11/8/2013 6:22 PM, Gleb Smirnoff wrote:
>>> On Fri, Nov 08, 2013 at 02:11:49AM -0330, Bear wrote:
>>> B> Hi all,
>>> B> I want to modify VLAN priority by ng_patch. After reading the
>>> B> manpage of
>>> B> ng_patch(http://www.freebsd.org/cgi/man.cgi?query=ng_patch) and
>> the
>>> B> example it given:
>>> B>
>>> B>  >  /usr/sbin/ngctl -f- <<-SEQ
>>> B>  > 	 mkpeer ipfw: patch 200 in
>>> B>  > 	 name ipfw:200 ttl_add
>>> B>  > 	 msg ttl_add: setconfig { count=1 csum_flags=1 ops=[	 \
>>> B>  > 		 { mode=2 value=3 length=1 offset=8 } ] }
>>> B>  >  SEQ
>>> B>  >  /sbin/ipfw add 150 netgraph 200 ip from any to
>>> B> simplex.remote.net
>>> B>
>>> B> It seems ng_patch can only modify IP header. However, the position
>>> B> of VLAN header is before IP header and after Ethernet header. How
>>> B> can I modify it?
>>>
>>> ipfw allows you to intercept packets at IP layer. Tp modify VLAN
>>> header, you need to capture them earlier. May be ng_ether(4) will
>> help you.
>>>
>
>
>
>