[bad udp cksum 0x4c91 -> 0x8abd!] So I was wondering if that could be the reason why the client/requestor was not able to receive the DNS response. If that is the case, how can I solve this problem? If that is not the reason, then I am really lost.. DNS_Res.py
Jun 17, 2008 · [tcpdump] how to fix the bad checksum problem If you capture packets using tcpdump directly from the server, your capture file may contain bad checksums. This is because your OS is currently configured to use the hardware checksum offloading feature of the NIC. # tcpdump -nvv -i bond0 multicast and port 18113 tcpdump: listening on bond0, link-type EN10MB (Ethernet), capture size 96 bytes 20:16:59.109023 IP (tos 0x0, ttl 1, id 0, offset 0, flags [DF], proto: UDP (17), length: 61) nn.nn.nn.nn.18113 > nn.nn.nn.nn.18113: [bad udp cksum 3965!] UDP, length 33 Environment. Red Hat Enterprise Linux (Any Version) Toni Mueller <[hidden email]> wrote: > today I see tons of these on a 4.6-stable/amd64 machine (sample): > > 17:21:00.848135 esp 1.1.1.1 > 2.2.2.2 spi 0x54d46678 seq 132642 len 84 > (DF) (ttl 64, id 49897, len 104, bad cksum 0! differs by 8b3c) This looks like outgoing packets on an interface that does IPv4 header checksumming in hardware. Jun 15, 2009 · Bad mount of .mdf - "wrong fs type, bad option, bad superblock, on /dev/loop0" Maybe-not: Linux - General: 2: 02-29-2008 01:30 PM: mount: wrong fs type, bad option, bad superblock on /dev/sda1: yekim: Linux - Hardware: 10: 07-05-2007 11:28 AM: mount: wrong fs type, bad option, bad superblock on /dev/cdrom, Adil_uk: Linux - Hardware: 9: 02-16 On Fri, Jul 8, 2011 at 12:44 AM, Anton Shterenlikht <[hidden email]> wrote: > I'm trying to troubleshoot tftpd(8). () > 192.168.232.10.15388 > buzi.tftp: [no cksum] 25 RRQ "/bsd.rd.IP32" octet ( > o > 23:25:21.024160 IP (tos 0x0, ttl 64, id 56, offset 0, flags [none], proto UDP (1 > 7), length 30, bad cksum 0 (->293a)!) > buzi.19330 > 192.168.232.10.15388: [udp sum ok] UDP, length 2 > 23:25 Dec 22, 2016 · 04:40:32.444077 90:1b:0e:27:89:0e > ea:55:66:5f:51:63, ethertype IPv4 (0x0800), length 65: (tos 0x0, ttl 64, id 51268, offset 0, flags [DF], proto UDP (17), length 51
The packets are generated by netcat with bad UDP checksum and a flag is set in the kernel to ignore it. It works with linux bridge because the packets stay in the kernel space, but when they pass through the softswitch the packets enter the user space and are reinsterted in the kernel without the inital flags that ignore bad checksum, so they
BOOTP/DHCP, Reply, length 323, xid 0x930ba16d, secs 3, Flags [none] (0x0000) Your-IP 10.0.0.2 Server-IP 10.0.0.3 Client-Ethernet-Address fa:16:3e:0e:04:32 (oui Unknown) Vendor-rfc1048 Extensions Magic Cookie 0x63825363 DHCP-Message Option 53, length 1: Offer Server-ID Option 54, length 4: 10.0.0.3 Lease-Time Option 51, length 4: 86400 RN Option In some cases the UDP checksums in packets from DHCP servers are incorrect. This is a problem for some DHCP clients that ignore packets with bad checksums. This patch inserts an iptables rule to ensure DHCP servers always send packets with correct checksums. Due to this bug DHCP offers are sometimes not accepted by Instances.
The packets are generated by netcat with bad UDP checksum and a flag is set in the kernel to ignore it. It works with linux bridge because the packets stay in the kernel space, but when they pass through the softswitch the packets enter the user space and are reinsterted in the kernel without the inital flags that ignore bad checksum, so they
Bad UDP checksums are a common case in the real networking world - either due to problematic NIC's or kernel bugs/cache failures. I noticed the following behavior for the SNMP plugin in a network where bad UDP checksums occur: SNMPget telegraf.49840 > active.hostname.snmp: [bad udp cksum 0xc05f -> 0xd256!] From the service side, SYN packets come in from the client, and SYN ACK packets try to go out from the service, but they are marked as bad packets. Every single one of them! The reason is because of a bad IP header checksum where the value is 0x00 instead of being 0x5338 (for example).