Within a single Interior Gateway Protocol (IGP) area, specifically in link-state protocols like OSPF or IS-IS, each router is responsible for two primary actions. First, it originates link-state advertisements (LSAs or LSPs) that describe its own state, including its connected interfaces, their costs, and its neighbors (C). This is how a router advertises information about itself. Second, it acts as a relay point. When a router receives a link-state advertisement from a neighbor, it forwards (floods) this information to its other neighbors within the area (D). This flooding mechanism ensures that all routers within the same area build an identical Link-State Database (LSDB), which is essential for accurate and consistent Shortest Path First (SPF) calculations.

A. Routers summarize information they learn from neighbors.

This is incorrect because route summarization in link-state IGPs is performed by Area Border Routers (ABRs) at the boundary between areas, not by every router within a single area.

B. Routers discard valid but inaccurate information from neighbors.

This is incorrect because routers in a link-state IGP do not have a mechanism to verify the "accuracy" of the content; they process any protocol-valid advertisement and flood it.

1. Moy

J. (1998). RFC 2328: OSPF Version 2. The Internet Society.

For Answer C: Section 1.2

"The OSPF protocol is a link-state routing protocol. Each router maintains a database describing the AS's topology... Each individual piece of this database is a particular router's local state (e.g.

the router's usable interfaces and reachable neighbors)." This confirms routers advertise their own state.

For Answer D: Section 13

"The Flooding Procedure

" describes the mechanism for propagating link-state updates. It states

"A router that has just received a link state update... must send the update out to some of its neighbors." This is the relay function.

For Incorrect A: Section 3.5

"Area border routers

" explains that these specific routers "condense the topological information from their attached areas for distribution to the backbone

" confirming summarization is an inter-area function.

2. Massachusetts Institute of Technology (MIT) OpenCourseWare. (2004). 6.829J / 16.440J Introduction to Networks

Lecture 10: Link State Routing.

For Answers C & D: Slide 10-5

"Basic Idea

" outlines the two phases of link-state routing: 1) "Reliable flooding: Tell all other routers what you know about your neighbors" and 2) "Path calculation (Dijkstra's algorithm)." The first phase encompasses both self-advertisement (what you know) and relaying (tell all other routers). This supports the concepts of originating and relaying information.