Read the header and coverage boundary
02Each of four header fields is16 bits. Checksum Coverage replaces UDP’s Length field and counts octets from the first UDP-Lite header octet, including all 8 header octets.
Separate malformed cases: coverage4 or25 for this24-octet datagram must be discarded.
Source for this drawing: RFC 3828 · Read RFC section 3.1 ↗
New to this? Start hereA quick picture + helpful background
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.
Helpful first, if these ideas are unfamiliar
These pictures are analogies to help you learn. The linked RFC explains the actual rules.
Terms in this drawing
Related RFCs and changes
“Updates” changes part of an earlier RFC. “Obsoletes” replaces it. This list shows selected related documents.
Coverage0 means the entire UDP-Lite datagram, not no checksum. Coverage8 means header-only coverage; the pseudo-header is still included.
- Coverage0 means the entire UDP-Lite datagram, not no checksum. Coverage8 means header-only coverage; the pseudo-header is still included.
- The receiver MUST discard coverage1–7 and coverage greater than the IP-provided UDP-Lite length. The header MUST always be covered.
- The actual datagram length comes from IP. The sender IP module MUST NOT append extra payload padding (§3.4).
The header diagram has two equal16-bit fields per row. The lower strip uses a common byte scale. Values12/24and the ports are worked examples, not mandatory settings.
Read the RFC section ↗