Date: Thu, 20 Jan 2005 10:33:33 +0000 (GMT) From: Robert Watson <rwatson@freebsd.org> To: Charlie Schluting <charlie@schluting.com> Cc: "freebsd-net@freebsd.org" <freebsd-net@freebsd.org> Subject: Re: vlans changed? Message-ID: <Pine.NEB.3.96L.1050120102946.84093B-100000@fledge.watson.org> In-Reply-To: <41EECAC0.3000801@schluting.com>
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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
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.
Robert N M Watson
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