Block receiving by default
02Receiving a directed broadcast at the router is one decision. RFC 2644 changes its default, rather than banning every use of broadcast.
Separate configuration example: if an implementation offers the option and the end user explicitly enables it, this receive gate permits arrival at the router. No forwarding outcome is implied.
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.
Replaces the receive and forward default-permit requirements with default blocking. Options to enable receiving and forwarding are optional, not mandatory.
Read the updated RFC section ↗A router MAY have a configuration option to allow receiving directed broadcasts. That option MUST be disabled by default.
- A router MAY have a configuration option to allow receiving directed broadcasts. That option MUST be disabled by default.
- The router MUST NOT receive Network Directed Broadcast packets unless specifically configured by the end user. The enable option is optional; do not assume every router provides one.
- This example uses a last-hop router that knows 192.0.2.0/24. Transit routers cannot identify a destination as directed broadcast merely by inspecting its last octet. Receiving here does not grant forwarding permission.
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 ↗