2/14/2023 0 Comments F5 tcpdump wiresharkftp "put" and "get" was done to send and receive data.įrame 453 is a large_receive packet received by 5.0.0.240.įrame 5999 is a large_send packet transmitted by 5.0.0.240. ftp client was ran on 5.0.0.70 and ftp server was ran on 5.0.0.240. Host - ipaddress 5.0.0.240 configured on 10 Gb physical adapter Which layer TCP and IP checksum are calculated and where iptrace is capturing the packet?įigure below shows the layer where TCP and IP checksum are calculated and where iptrace/tcpdump captures the packets. The large_receive also known as Large Receive Offload (LRO). The large_receive is a device driver attribute and it is enabled by default. The CPU has to process fewer packets then when large_receive is disabled, which reduces CPU usage. When large_receive is enabled, Physical Layer calculates TCP and IP checksum, and receive packets into larger packets before passing them up the stack. The large_send is also known as TCP Segmentation Offload (TSO). The large_send is a device driver attribute and it is enabled by default. The Ethernet adapter then does the TCP segmentation offload to segment the data into the MTU sized packets, calculates TCP and IP checksum. When large_send is enabled, TCP can send up to 64K bytes of data with one call down the stack, which reduces host processing and reduces CPU usage. To understand the reason for this behavior, lets understand large_send, large_receive and which layer iptrace is capturing the packet. When iptrace and tcpdump collected on aix/vios host is read using wireshark, it marks TCP checksum and IP checksum fields as incorrect even though communication is working fine.
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