From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ben Greear Subject: Re: hard_start_xmit and Linux bridging Date: Thu, 09 Sep 2004 16:30:10 -0700 Sender: netdev-bounce@oss.sgi.com Message-ID: <4140E782.2000505@candelatech.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Cc: netdev@oss.sgi.com Return-path: To: Lewis Adam-CAL022 In-Reply-To: Errors-to: netdev-bounce@oss.sgi.com List-Id: netdev.vger.kernel.org Lewis Adam-CAL022 wrote: > Hi all, > > I tried going to the bridge@lists.osdl.org for this question but got no response, I'm hoping somebody here has had a similar experience as me. > > Basically, I put my wlan0 driver in a bridge with eth0. When my hard_start_xmit() function is called (as a result of a packet received on eth0 and bridged to my driver), the skb that I am passed contains an extra four bytes (e.g. the Ethernet FCS). > > In my mind, this should be stripped off. But I have looked at all the open source net drivers I could find and nobody seems to care. Is there a way to know if the skb has been forwarded by a bridged interface? If I forward on the extra bytes, then a 1500 byte packet becomes 1504 and fails the MTU check on the other side of the wireless interface (when it is passed back to eth0). > > TIA, > Adam I added some ioctls to allow one to turn on the ability to receive the CRC, but I don't know of any drivers that include it by default. What driver/hardware is your eth0 device? How are you determining the size, by the skb->len ? Does tcpdump/ethereal show the extra 4 bytes if you sniff eth0 w/out bridging? Ben -- Ben Greear Candela Technologies Inc http://www.candelatech.com