Thanks for the information, Marc. Just to close the loop on this problem, I determined that my problem had nothing to do with the "send" side on the ROACH. I thought that it was necessary to set mtu to 9000 on the send side (i.e. ifconfig tap3 mtu 9000), but this was incorrect. I was able to get packets simply by increasing the MTU to 9000 on the receive side, even though the send side still has MTU 1500. I had another problem (clock issue) that kept me from getting packets.
Regards, Dale ________________________________________ From: Marc Welz [m...@ska.ac.za] Sent: Monday, January 09, 2012 3:18 AM To: Gary, Dale Cc: casper@lists.berkeley.edu Subject: Re: [casper] Problem with tap? On Fri, Jan 6, 2012 at 2:20 AM, Gary, Dale <g...@adm.njit.edu> wrote: > 4 S root 615 596 1 80 0 - 448 select 12:52 ? 00:00:00 tgtap -b > /proc/614/hw/ioreg/gbe0 -a 10.0.0.20 -t tap3 -m 02:02:0A:00:00:14 -p 60000 > > So the command is arriving at the ROACH in the right format, and I suppose > ifconfig just does not display it as I expect. Still, I am not getting any > packets. Hello By way of explanation: The tap device is used to interface the kernel with the 10Gbe interface. So things like ping packets will traverse the interface, but data frame generated by gateware will not. So if you look at the output of ifconfig, the packet count will go up if you ping the roach10Gbe interface from a remote system, but the counter won't tick over for gateware data. The tap device we use also doesn't actually get an ethernet header from the kernel, it receives the bare IP packets (similar to say slip - note the POINTOPOINT and NOARP flags in ifconfig below). For the other direction, tgtap strips off ethernet frame headers before it sends packets down the tap device for processing by the kernel. This is possible because tgtap manages arp for both kernel and gateware. Hence the hardware address displayed by ifconfig is irrelevant. > tap3 Link encap:UNSPEC HWaddr > 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00 > inet addr:10.0.0.20 P-t-P:10.0.0.20 Mask:255.255.255.0 > UP POINTOPOINT RUNNING NOARP MULTICAST MTU:1500 Metric:1 > RX packets:0 errors:0 dropped:0 overruns:0 frame:0 > TX packets:0 errors:0 dropped:0 overruns:0 carrier:0 > collisions:0 txqueuelen:500 > RX bytes:0 (0.0 b) TX bytes:0 (0.0 b) > regards marc
