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Kernel Eth0 Ipv4 Checksum Error

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Incorrect Checksum Tcpdump

Pulse Graphs New issue IPv6 Checksum error with kernel 4.2 #1083 Closed bad udp checksum tcpdump Belphemur opened this Issue Jul 21, 2015 · 8 comments Projects None yet Labels None yet Milestone

Tcp Checksum Incorrect Wireshark

No milestone Assignees No one assigned 5 participants Belphemur commented Jul 21, 2015 Raspberry Pi B 256 MB. Current kernel branch 4.2 with bcmrpi_defconfig + zswap + zbud + linux disable checksum offload lz4. Triggering app: syncthing. and swapper. Router TPLink TL-WR841N with OpenWRT and IPv6 for local lan + IPv4. Raspberry Pi have openvpn installed and configured (but not used when the error arise). Full dmesg log with all the StackTrace: http://pastie.org/10304133 Ifconfig: br0 Link encap:Ethernet HWaddr b8:27:eb:fc:dd:77 inet addr:192.168.42.2 Bcast:192.168.42.255 Mask:255.255.255.0 inet6 addr: fe80::545e:b8ff:fe97:cb51/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX disable udp checksum linux packets:59523 errors:0 dropped:0 overruns:0 frame:0 TX packets:24568 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:28257772 (26.9 MiB) TX bytes:73773783 (70.3 MiB) eth0 Link encap:Ethernet HWaddr b8:27:eb:fc:dd:77 inet addr:192.168.42.2 Bcast:192.168.42.255 Mask:255.255.255.0 inet6 addr: fe80::ba27:ebff:fefc:dd77/64 Scope:Link UP BROADCAST RUNNING PROMISC MULTICAST MTU:1500 Metric:1 RX packets:59778 errors:0 dropped:0 overruns:0 frame:0 TX packets:65460 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:28282513 (26.9 MiB) TX bytes:76734164 (73.1 MiB) lo Link encap:Local Loopback inet addr:127.0.0.1 Mask:255.0.0.0 inet6 addr: ::1/128 Scope:Host UP LOOPBACK RUNNING MTU:65536 Metric:1 RX packets:5511 errors:0 dropped:0 overruns:0 frame:0 TX packets:5511 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:550126 (537.2 KiB) TX bytes:550126 (537.2 KiB) tap0 Link encap:Ethernet HWaddr 56:5e:b8:97:cb:51 inet6 addr: fe80::545e:b8ff:fe97:cb51/64 Scope:Link UP BROADCAST RUNNING PROMISC MULTICAST MTU:1500 Metric:1 RX packets:0 errors:0 dropped:0 overruns:0 frame:0 TX packets:6622 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:100 RX bytes:0 (0.0 B) TX bytes:2583973 (2.4 MiB) Br0 -> eth0 & tap0 P33M commented Jul 27, 2015 Is this a regression between the current stable (4.0.y) branch and 4.2? 4.2 is still in -rc. Belphemur commented Jul 27, 2015 Yes it wasn't happening in the 4.0.y neither 4.1.y. I k

9 Comments If you've ever tried to trace a UDP or TCP stream by using the tcpdump tool on Linux then

Bad Udp Cksum Snmp

you may have noticed that all, or at least most, packets indicate tcp checksum offloading checksum errors. This is caused because you have checksum offloading on your network card (NIC) and tcpdump reads

Ntp Bad Udp Cksum

IP packets from the Linux kernel right before the actual checksum takes place in the NIC's chipset. That's why you only see errors in tcpdump and your network traffic https://github.com/raspberrypi/linux/issues/1083 works ok. So, just to prove my point, here is a tcpdump output while monitoring DNS traffic (udp/53) $ sudo tcpdump -i eth0 -vvv -nn udp dst port 53 tcpdump: listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes 17:04:48.145904 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto UDP (17), length 61) 10.0.0.2.56497 https://sokratisg.net/2012/04/01/udp-tcp-checksum-errors-from-tcpdump-nic-hardware-offloading/ > 10.0.0.1.53: [bad udp cksum 0x8f54 -> 0xb8fc!] 30234+ AAAA? www.twitter.com. (33) 17:04:48.145925 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto UDP (17), length 61) 10.0.0.2.56497 > 10.0.0.1.53: [bad udp cksum 0x224d -> 0x2604!] 30234+ AAAA? www.twitter.com. (33) After checking active NIC hardware offloading options you can see the obvious $ sudo ethtool -k eth0 | grep on rx-checksumming: on tx-checksumming: on scatter-gather: on generic-segmentation-offload: on generic-receive-offload: on rx-vlan-offload: on tx-vlan-offload: on After disabling TCO (tcp offloading) for TX/RX on the NIC the problem is gone $ sudo ethtool -K eth0 tx off rx off $ sudo tcpdump -i eth0 -vvv -nn udp dst port 53 tcpdump: listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes 17:06:09.355411 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto UDP (17), length 57) 10.0.0.2.18964 > 10.0.0.1.53: [udp sum ok] 292+ AAAA? twitter.com. (29) 17:06:09.355431 IP (tos 0x0, ttl 64, id 0, offset 0, flags [DF], proto UDP (17), length 57) 10.0.0.2.18964 > 10.0.0.1.53: [udp sum ok] 292+ AAAA? twitter.co

here for a quick overview of the site Help Center Detailed answers to any questions you might have Meta Discuss the workings and policies of this site About Us Learn more about Stack Overflow http://stackoverflow.com/questions/22101650/how-can-i-receive-the-wrong-ethernet-frames-and-disable-the-crc-fcs-calcul the company Business Learn more about hiring developers or posting ads with us Stack Overflow Questions Jobs Documentation Tags Users Badges Ask Question x Dismiss Join the Stack Overflow Community Stack Overflow is a community of 6.2 million programmers, just like you, helping each other. Join them; it only takes a minute: Sign up How can i receive the wrong Ethernet frames and disable the CRC/FCS calcul? up vote 2 down vote favorite bad udp I generate a traffic between two PCs (using C and Python by sending Ethernet frames), the goal of this is to capture some errors frames. The problem is when the Phy layer detect an error on a frame (if the CRC or FCS is not valide) the frame is dropped and i can't receive it in my program. Are the any way to receive the wrong frame (disable the drops in the bad udp cksum Phy layer and receiving a indicator that indicate that this frame is wrong for example) and how can i consult the statistic of the NIC card (number of drops ...etc) "I'm using Python and C" Thank you. python c ethernet crc32 share|improve this question asked Feb 28 '14 at 17:14 A2maridz 1825 This is going to depend on the platform. You'll need to make some sort of device driver ioctl() call assuming the driver supports that. –Tall Jeff♦ Feb 28 '14 at 23:11 Yes i'm traying to find a way that the device don't drop the bad frames (deliver them and notify me that they are bad) –A2maridz Mar 6 '14 at 7:23 add a comment| 2 Answers 2 active oldest votes up vote 3 down vote You didn't specify which OS, but I can at least speak for Linux: It may on your kernel, NIC and driver as well as ethtool versions. We need to tell the driver/hardware to do two things it doesn't normally do: 1) Pass the FCS field up the networking stack. (Generally this gets truncated before being passed up) 2) Not drop packets with bad FCS fields, instead pass them up as-is There are two ethtool options to achieve each of these: ethtool -K eth0 rx-fcs

 
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