Re: em promiscuous mode bug?

On Mon, Jul 31, 2006 at 01:25:59PM +0200, Ian FREISLICH wrote:
 > Pyun YongHyeon wrote:
 > > On Mon, Jul 31, 2006 at 07:16:03AM +0200, Ian FREISLICH wrote:
 > >  > Pyun YongHyeon wrote:
 > >  > > Hardware VLAN tagging was disabled in em(4) when it operates
 > >  > > in promiscuous mode and em(4) will insert a VLAN tag in the
 > >  > > driver.
 > >  > 
 > >  > Um, no.  When an em interface with hardware VLAN tagging enabled
 > >  > is placed in promiscuous mode, it just _stops_ tagging.  Entirely.
 > >  > The 802.1Q vlan just breaks.
 > >  > 
 > > 
 > > Would you try latest em(4) in CURRENT?(if_em.c, rev. 1.122)
 > 
 > No change with r1.122 (used to be r1.116).  Note that with
 > VLAN_HWTAGGING enabled, both hosts bring up their carp interface
 > as master.  This is because none of the frames are tagged when the
 > carp driver puts the vlan interface which in turn puts the em
 > interface into promiscuous mode.
 > 
Then I have no clue.  I'm not familiar with carp(4) but I guess
carp(4) has nothing to do with em(4).

 > You stated that in an earlier email that VLAN_HWTAGGING is disabled
 > when the interface is placed in promiscuous mode.  Is there any

See cvs logs if_em.c, rev 1.58.

 > reason for this appart from not being to view the VLAN header with
 > tcpdump?  My site runs a lot of VLANS (500+) and it would be nice
 > to offload this work to the card.
 > 

Normally you can't see VLAN information with tcpdump if your NIC
supports VLAN_HWTAGGING. On Tx side the VLAN information is carried
with a mbuf tag and the hardware is programmed to send the VLAN id
from the mbuf tag. On Rx side the hardware performs VLAN tag stripping
before tcpdump see the received packet. You have to disable
VLAN_HWTAGGING to see VLAN header with tcpdump.

If you need real hardware VLAN tag stripping/insertion in promiscuous
mode switch your NIC with other cards such as bge(4)/bce(4).

-- 
Regards,
Pyun YongHyeon