To verify the check sum of an API packet add all bytes including the checksum (do not include the delimiter and length) and if correct, the last two far right digits of the sum will equal FF. If an API data packet is composed with an incorrect checksum, the XBee/XBee-PRO Zigbee RF Module will consider the packet invalid and will ignore the data. 0x3B is the checksum for this data packet. Subtract 0xC4 from 0xFF and you get 0x3B (0xFF - 0xC4 = 0x3B). Now take the result of 0x01C4 and keep only the lowest 8 bits which in this example is 0xC4 (the two far right digits). To calculate the check sum you add all bytes of the packet, excluding the frame delimiter 7E and the length (the second and third bytes):Ġx08 + 0x01 + 0x4E + 0x49 + 0x58 + 0x42 + 0x45 + 0x45 = 0x01C4 if you want MTU for QinQ over physical Ethernet links, just add QinQ, as your physical link. Protocol overhead values here are just what they add to the frame. for TCP over IPv6 encapsulated into GRE over IPv4, add IPv4, GRE, IPv6, and TCP. If the checksum is correct, the last two digits on the far right of the sum equal 0xFF.Ĭonsider the following sample data packet: 7E 00 08 08 01 4E 49 58 42 45 45 3B Byte(s) // ICMP header checksum (16 bits): set to 0 when calculating checksum icmphdr.icmpcksum 0 // Prepare packet. If you want to calculate TCP MSS, add the underlying protocol and TCP after tunnel protocols.You can click the same protocol button more than once, e.g. if you click Ethernet, you will see VLAN and QinQ header option checkboxes. Some protocols have additional options, e.g. Click protocol buttons to add protocols to the stack. Now, to calculate the IP header algorithm one must know the basic header structure of IP protocol. Add all bytes including the checksum do not include the delimiter and length. This tool allows you to easily see what each protocol adds to your packet. IP header checksum is calculated over IP header only as the data that generally follows the IP header (like ICMP, TCP etc) have their own checksums.Keep only the lowest 8 bits from the result.
For IPv4 this pseudo header consists of the 32-bit source. Add all bytes of the packet, except the start delimiter 0x7E and the length (the second and third bytes). Except for the TCP and UDP packet the IP pseudo header must also be included in the calculation.
To calculate the checksum of an API frame:
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