vlans changed?

[Maxim Konovalov]

On Thu, 20 Jan 2005, 10:33-0000, Robert Watson wrote:

>
> On Wed, 19 Jan 2005, Charlie Schluting wrote:
>
> > Now, in 5.3, the only thing I can get working is to configure the em0
> > int with the IP, and set the trunk to have the native vlan corresponding
> > to that IP. Weird.
> >
> > Also, is there a way to stop em(4) from stripping dot1q tags in
> > hardware? I'd like to see them with tcpdump. What kind of a performance
> > hit does this involve?
>
> Try "ifconfig em0 -vlanhwtag" and see if that helps.  If not, take a look

Yep, it works for Alex (CC'ed), thanks for the tip.

> in if_em.c:em_setup_interface(), and you'll see two lines like this:
>
> #if __FreeBSD_version >= 500000
>         ifp->if_capabilities |= IFCAP_VLAN_HWTAGGING | IFCAP_VLAN_MTU;
>         ifp->if_capenable |= IFCAP_VLAN_HWTAGGING | IFCAP_VLAN_MTU;
> #endif
>
> Delete the contents "|FCAP_VLAN_HWTAGGING |" from each line, and that
> should disable support for hardware vlan tagging and stripping in the
> driver.  There are several bugs relating to the handling of hardware vlan
> tagging and promiscuous mode in both if_re and if_em.  I had hoped to have
> a chance to resolve them over the past couple of months but have not as
> yet been able to do so.  I measured a small performance hit last time I
> tried disabling the hardware tagging, perhaps a couple of percent, but
> mileage may vary -- for in-bound packets, there's a small amount
> additional work, but for outgoing packets you may see an extra memory
> allocation for each encapsulated packet (it depends a bit on what you
> send).  If this appears to work properly for you, we should probably
> commit the change so that what's in the tree works properly, even if it's
> slightly slower.

IMO this is a good idea.

-- 
Maxim Konovalov