Compose and extract an address
03Use the configured prefix length in both directions. The /48 worked example makes the reserved-byte boundary visible.
Using /48, extraction yields c0 00 02 21, or 192.0.2.33. Taking only the last 32 IPv6 bits here would recover zeros and be wrong.
Source for this drawing: RFC 6052 · Read RFC section 2.3 ↗
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.
Extraction must use the configured prefix and layout.
- Extraction must use the configured prefix and layout.
- Compose the prefix, the IPv4 bits and a suffix; for a prefix shorter than /96 insert the null u octet at bits 64–71 and keep the result 128 bits.
- For extraction below /96, remove u and take the 32 bits after the prefix. For /96, take the last 32 bits. Nonzero suffix values SHOULD be ignored as zero, absent a future extension; that recommendation does not waive the u MUST.
Chosen operations use Table 1’s /48 prefix 2001:db8:122::/48 and 192.0.2.33. The helper validates configured-prefix matching and the reserved byte as teaching preconditions; it is not a complete translator. No requirement to reject every nonzero suffix is invented. These drawings show byte placement rather than network transmissions.
Read the RFC section ↗