Networking/Discussion/Technology/Where does vlan tag get added to the transmitted Ethernet packet?/List of Posts
 
Forum Topic - Where does vlan tag get added to the transmitted Ethernet packet?:
   
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Yuh-Fwu Guu
01/17/2011 10:17 AM
post82416
Where does vlan tag get added to the transmitted Ethernet packet?   
When sending a packet of data using sendto() through a vlan, the received packet has vlan tag attached at the end of the
 MAC header and before the IP header. Where does the tag get added to the transmitted packet? Is it in the socket 
library? io-pkt? network driver? or somewhere else?

I am getting dual vlan tag at the receive node (please see the packet data below), and I am trying to figure out why I 
am getting double vlan tags.

0x0000: 0100 5E28 1114 0018 4405 050A 8100 0000
0x0010: 8100 044A 0800 4500 0050 BC4F 0000 0100

Thanks for any help...
(I am using e1000 driver with 82576)
Vineet Garg
01/17/2011 1:05 PM
post82425
Re: Where does vlan tag get added to the transmitted Ethernet packet?   
at least with io-net I am sure that VLAN tag is added by io-net itself and
network driver gets the entire frame including the VLAN tag. Not sure if
this is any different in io-pkt stack.

are you sure there is no other network switch between your transmitter and
receiver who could be adding this double tag..?

Regards
VG

On Mon, Jan 17, 2011 at 8:47 PM, Yuh-Fwu Guu <community-noreply@qnx.com>wrote:

> When sending a packet of data using sendto() through a vlan, the received
> packet has vlan tag attached at the end of the MAC header and before the IP
> header. Where does the tag get added to the transmitted packet? Is it in the
> socket library? io-pkt? network driver? or somewhere else?
>
> I am getting dual vlan tag at the receive node (please see the packet data
> below), and I am trying to figure out why I am getting double vlan tags.
>
> 0x0000: 0100 5E28 1114 0018 4405 050A 8100 0000
> 0x0010: 8100 044A 0800 4500 0050 BC4F 0000 0100
>
> Thanks for any help...
> (I am using e1000 driver with 82576)
>
>
>
> _______________________________________________
>
> Technology
> http://community.qnx.com/sf/go/post82416
>
>
Yuh-Fwu Guu
01/17/2011 2:13 PM
post82426
Re: Where does vlan tag get added to the transmitted Ethernet packet?   
The transmit and receive nodes are connected directly to each other via a crossover cable for testing, there is nothing 
in between. Tcpdump shows the dual vlan tags.

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