Messages in this thread |  | | Date | Wed, 07 Nov 2001 11:03:58 -0500 | From | Jeff Garzik <> | Subject | Re: [PATCH] 802.1q-support for 3c59x.c |
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Andreas Ferber wrote: > > Hi, > > I was very pleased that 802.1q VLAN tagging support has been included > into the kernel recently :-) > > Though this is only part of the work needed. > > Let me start from the beginning, for those not familiar with 802.1q > tagging. The tag adds an additional header field (4 Bytes) to the > ethernet header, so that the maximum frame size is 1518 Octets instead > of 1514 (with a standard MTU of 1500). > > The problem is that most network cards by default will flag those > frames as oversized and drop them (though /sending/ tagged frames is > not a problem with any card I know of). There are several > possibilities to resolve this problem: > > - reduce the MTU on all servers connected to the VLAN (not always > possible) > - patch the NIC driver so that it doesn't drop oversized frames > - set the MTU on the physical interface to 1504, which is a) not > possible with every driver, and b) untagged frames sent via the > interface will be oversized now. > > Below my signature you will find a patch that adds the necessary bits > to the 3c59x.c driver. It sets up the NIC to receive VLAN tagged > frames and (if supported by the NIC) correctly checksum them. > > Newer cards (those with HW checksumming support) have a register to > configure the maximum frame size. Older cards don't have this > register, but they have a flag that lets the NIC receive FDDI sized > frames (4500 Octets IIRC). > > It was discussed on the VLAN mailinglist if (at least in the case of > hardware like the old 3Com NICs where you can basically only disable > checking the frame size) it is feasible to only enable the large > frame receipt if VLAN tags are really used on the NIC. We have come to > the conclusion that uncoditionally enabling it should not pose any > performance penalties with any sane hardware implementation, so we > decided to not introduce a VLAN enable callback into NIC drivers. > > Just to be sure, the 3c59x patch only enables the new parts if 802.1q > support has been enabled in the kernel configuration. Testing proved > the patch quite stable (no problem reports so far). > > There is no maintainer mentioned for the 3c59x driver in the > MAINTAINERS file, so I send this directly to the list. Please consider > the patch for kernel inclusion. > > Andreas > -- > Andreas Ferber - dev/consulting GmbH - Bielefeld, FRG > --------------------------------------------------------- > +49 521 1365800 - af@devcon.net - www.devcon.net > > --- linux.orig/drivers/net/3c59x.c Sun Sep 30 21:26:06 2001 > +++ linux/drivers/net/3c59x.c Wed Oct 24 21:52:10 2001 > @@ -308,6 +308,9 @@ > code size of a per-interface flag is not worthwhile. */ > static char mii_preamble_required; > > +/* The Ethernet Type used for 802.1q tagged frames */ > +#define VLAN_ETHER_TYPE 0x8100
This needs to be ETH_P_8021Q from if_ether.h.
Have you tested this? I should think you would need a dev->change_mtu also.
-- Jeff Garzik | Only so many songs can be sung Building 1024 | with two lips, two lungs, and one tongue. MandrakeSoft | - nomeansno
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