Compute the mandatory checksum
03A pseudo-header is checksum input derived from IP, not extra bytes transmitted inside UDP-Lite. Its length is the full UDP-Lite datagram length even when coverage is partial.
Complement the sum and place the checksum into the actual header.
Source for this drawing: RFC 3828 · Read RFC section 3.2 ↗
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A message needs an address.
Think of a packet as a small addressed envelope. Devices pass it onward; transport protocols decide what delivery promises an application gets.
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The checksum MUST include the pseudo-header regardless of coverage. IPv4 and IPv6 have different pseudo-header layouts; this example uses IPv4.
- The checksum MUST include the pseudo-header regardless of coverage. IPv4 and IPv6 have different pseudo-header layouts; this example uses IPv4.
- Set the Checksum field to zero before calculation. Sum the pseudo-header and selected prefix as16-bit words, adding a virtual zero octet for an odd byte count.
- Take the one’s complement of the folded sum. A computed zero is transmitted as all ones (FFFF); the transmitted Checksum field MUST NOT be all zeroes.
Documentation addresses192.0.2.1and198.51.100.2, source port50000, destination port5004and payload bytes00..10hex are a deterministic example. Virtual padding is calculation-only; the wire datagram remains25 octets.
Read the RFC section ↗