Separate origination from source addresses
04Originating a packet means the router creates it itself. That permission is distinct from receiving or forwarding someone else’s directed broadcast.
Separate invalid packet: source 198.51.100.255 is the directed broadcast of the example /24. The MUST NOT rule stops this use before transmission, regardless of the destination.
Source for this drawing: RFC 2644 · Read RFC section 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.
A router MAY originate Network Directed Broadcast packets. MAY is permission, not a requirement to send them and not an instruction to enable receiving or forwarding.
- A router MAY originate Network Directed Broadcast packets. MAY is permission, not a requirement to send them and not an instruction to enable receiving or forwarding.
- The directed broadcast address MUST NOT be used as a source address. A permitted broadcast destination does not make the same address valid in the source field.
- These are separate illustrative packets, not a live exchange. The default-blocking changes do not ban all router-originated broadcasts or replace other source validation and routing rules.
Fictional documentation addresses and a last-hop router that knows the destination prefix. A bounded teaching illustration, not a router configuration or packet tool.
Read the RFC section ↗