If the IP addresses are genuine, the bad packets are coming from a different Internet Service Provider's network. It is normally usable within a single organization only: normally there should be no need to allow UDP/5353 traffic through the border firewall of your organization, neither in- nor outbound. UDP/5353 is normally used by MDNS: multicast DNS, a peer-to-peer hostname resolution and service discovery protocol. The function is aware of hardware offloading features.Īs far as I can see, if the checksums are handled in hardware, this message means that the hardware actually detected a bad checksum in a received UDP packet. These messages come directly from the kernel, from the _udp4_lib_rcv() function located in net/ipv4/udp.c in Linux kernel source. This is not tcpdump or wireshark output, but a part of dmesg listing. Also, keep in mind, when looking at logs, or debugging network issues, that what you see at kernel level is not necessarily what will be seen at wire level. TLDR Those "errors" are a regular sight on Linux VMs, and nothing to obsess about once you know they are part of your baseline. Is showing the checksum calculated on kernel level.įrom UDP / TCP Checksum errors from tcpdump & NIC Hardware OffloadingĪfter checking active NIC hardware offloading options you can see theĪfter disabling TCO (tcp offloading) for TX/RX on the NIC the problemīe sure to turn back on the optimizations after finishing debugging network problems, as you have a small performance hit while they are off. Network is working properly: it is nothing to worry about because theĬhecksum is actually calculated on the network adapter and the tcpdump Incorrect in tcpdump output, without any packet errors and your If you have offload features enabled and you see cksum UDP / TCP Checksum errors in tcpdump output
#Snes9x bad checksum how to
See also Linux Networking: How to disable/enable offload features, RX/TX checksum, scatter, gather and beyond This saves on the CPU and importantly cuts down on the Packets, it allows the NIC to use its own processor to perform the That is, instead of the OS using the CPU to segment TCP Offloaded by the operating system to the Network Interface Card (NIC).Ĭommon operations for offloading are segmentation and checksumĬalculations. One case in which this occurs is when TCP/IP operations are Unfortunately sometimes what we see in Wireshark is not what weĮxpect. See Segmentation and Checksum Offloading: Turning Off with ethtool Hence when using tcpdump or looking at system logs, not seeing the right checksums at OS/VM level. VMWare does it, and I think KVM does it too (and not only).
The NIC is responsible for the checksum, and so it is not done at CPU level, to save CPU resources. Those "UDP errors" is UDP Checksum offloading. Turbo disabled by BIOS or unavailable on processor perf: interrupt took too long (6247 > 6167), lowering kernel.perf_event_max_sample_rate to 32000
ixgbe 0000:04:00.0: invalid short VPD tag 06 at offset 4 nr_pdflush_threads exported in /proc is scheduled for removal From the dmesg we get very strange lines as raid6: using avx2x2 recovery algorithm
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