[VLAN] Re: newbie question on enabling vlan feature in the driver

[Ard van Breemen]

On Wed, Mar 14, 2007 at 11:47:49AM -0700, kmk wrote:
> Ben, I enabled vlan in the eth mac by writing to vlan1tag and
> adjust mtu to handle vlan. Now, when I ping from a remote pc
> which also has vlan enabled interface, I don't see vlan tags in
> the frames. Same issue if I ping the remote PC.  Basically, I
> don't see vlan tag in tx/rx directions.

You should either:
- Complete your hardware "accelerated" vlan implementation
- do not use it at all, and make sure you can have 1504 MTU
  sizes, and make sure the hardware doesn't do funky stuff with
  the tag in the frame.

Hardware acceleration means the tag gets stripped and you get a
tagless frame in userspace with tcpdump, on both the ethX device
as well as the ethX.Y device. (And on outgoing it will be added.)
If you use pure software, the tag is still visible on at least
the ethX device.
I am not sure if hardware acceleration actually accelerates
anything. I've yet to see any benchmarks that proofs that
acceleration actually accelerates anything.

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