Check forwarding separately
03A last-hop router can deliver one directed broadcast onto the destination network. Receiving and forwarding have separate optional controls and both default to blocking.
In a separate configuration, both supported controls are explicitly enabled and other checks permit delivery. One link broadcast can be received by multiple hosts; replies are not required by this RFC.
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 ↗RFC 2644 §3 says a router MAY have options to enable receiving on an interface and to enable forwarding network-prefix-directed broadcasts. These options MUST default to blocking receipt and forwarding.
- RFC 2644 §3 says a router MAY have options to enable receiving on an interface and to enable forwarding network-prefix-directed broadcasts. These options MUST default to blocking receipt and forwarding.
- The worked forwarding comparison assumes receipt was explicitly enabled. With forwarding blocked, no broadcast is emitted onto the destination LAN. LAN means local area network.
- Explicitly enabling a supported forwarding option can allow a broadcast onto the target link, subject to other applicable routing and policy checks. It does not require each host to answer or guarantee application success.
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 ↗