TCP CHECKSUM DRIVER
TCP CHECKSUM FREE

Also the beauty of hash function is that its one way hash. This is the reason its used for file integrity verification. Its designed to be really strong, and does not have any sort of collision.

TCP CHECKSUM FREE

MD5 and SHA1 concentrates more making collision free outputs. Because it should be unique for a particular data. If there is two different set of data with same hash output, then that beats the purpose. It's nothing but the surety about the fact that 'No two hash outputs will have the same value'. Because the need is different in each case.Д¬ollision is the most important factor in hash algorithms. The method used by internet communication and hash algorithms are similar, but not exactly same. The TCP and UDP data verification) does not leverage MD5 or SHA1. However Internet communication(the core network data verification. MD5 and SHA1 are primarily used to verify integrity of files. This is because you can calculate the hash value on the file that you downloaded, and then if it matches the one that is mentioned in the website, you can have the surety that the file is not corrupted/and is unaltered. You might have noticed websites that provides MD5 & SHA1 hash values of the file that you want to download. Some of the popular hash algorithms are MD5, SHA1 etc. Thanks to cryptographers who designed hash algorithms. If both the values(of the sender and the receiver) tallies, then the data is uncorrupted/unaltered. Once the data is received, the receiver also calculates the checksum. The value calculated is either sent along with the message, or through other methods. Generally what happens is this.The sender calculates a short checksum value(very small in size) which represents the message/data that is being sent.

Whatever may be the case, there needs to be a method where the receiver can verify and figure out easily if the data is altered or corrupted. Below are the example of ACK and SYN packets showing IP and TCP checksum are not marked incorrect because large_send and large_receive are not done.When you send and receive data over the wire, there are possibilities where the data can get corrupted, altered, or modified(it can be accidental, purposely done with evil intention). The large_send and large_receive are not done for small data packets and control packets such as SYN, ACK, FIN, RST.Since values in the packets are dummy value so comparison fails and it marks IP checksum and TCP checksum as incorrect even though packet is valid. When iptrace (or tcpdump) is read using wireshark, it calculates the IP checksum and TCP checksum and compares with the value in the packets.5a8 in hex for MTU 1500) are filled in IP checksum and TCP checksum fields respectively. For large_send transmitting packet, the dummy value ffff and MTU size (e.g.For large_receive receiving packet, the dummy values ffff and 0 are filled in IP checksum and TCP checksum fields respectively.ftp 'put' and 'get' was done to send and receive data.ДЇrame 453 is a large_receive packet received by 5.0.0.240.ДЇrame 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?ДЇigure 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).

TCP CHECKSUM DRIVER

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.

Tcp checksum