Send routes with their masks
01DHCPv4 can give a client routes to particular IPv4 networks, each with an explicit mask and a next-hop router.
A separate example default route uses width 0 followed immediately by 198, 51, 100, 1. Its data length is five.
Source for this drawing: RFC 3442 · Read RFC source: Classless Route Option Format (unnumbered; page 3) ↗
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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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These pictures are analogies to help you learn. The linked RFC explains the actual rules.
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Related RFCs and changes
“Updates” changes part of an earlier RFC. “Obsoletes” replaces it. This list shows selected related documents.
A route describes a destination network and how to reach it.
- Option code 121 carries one or more destination descriptors, each followed by a four-octet router address. Its minimum data length is five octets.
- A descriptor begins with a mask width, then only the significant destination octets. Width means the number of one bits in the subnet mask.
- A default route uses width 0, no destination octets, and the four router octets. Length excludes the Code and Len octets.
All addresses here are fictional documentation or private examples. RFC 3442 updates RFC 2132: its option replaces option 33, not the entire older publication.
Read the RFC section ↗