CCNA2 - Chapter 10

Link-State Routing Protocols : Link-State Routing Protocols Routing Protocols and Concepts – Chapter 10

Objectives : Objectives Describe the basic features & concepts of link-state routing protocols. List the benefits and requirements of link-state routing protocols. Key Terms Link-state Routing Protocol Shortest Path First Link-state Packet Link-state Database

Who’s Responsible for Link-State Protocols? : Who’s Responsible for Link-State Protocols? Dijkstra's algorithm, solves the single-source shortest path problem for a directed graph with nonnegative edge weights. Wikipidia Edsger Dijkstra

Link-State Routing Protocols : Link-State Routing Protocols Also known as shortest path first algorithms These protocols built around Dijkstra’s SPF

Difference Between LS and DV Protocols : Difference Between LS and DV Protocols Distance Vector protocols understand distant networks based on direction (example: signs) Link State protocols create a topology (example: map)

Step 1: Determine Connected Networks : Step 1: Determine Connected Networks Router identifies directly connected networks Includes: Link - Router Interface State - Information about the condition of the links

Step 2: Establish Neighbor Adjacencies : Step 2: Establish Neighbor Adjacencies Hello packets are exchanged between routers with connected interfaces Once routers learn it has neighbors they form an adjacency - Two adjacent neighbors will exchange hello packets -These packets will also serve as keep alives Verify that neighbor and states have not changed

Step 3: Builds the Link-State Packet : Step 3: Builds the Link-State Packet Each router builds its own Link State Packet (LSP) Contents of LSP: - State of each directly connected link - Includes information about neighbors such as neighbor ID, link type, & bandwidth.

Step 4: Flooding LSP’s to Neighbors : Step 4: Flooding LSP’s to Neighbors Once LSP are created they are forwarded out to neighbors Neighbors store the LSP’s in a database After receiving the LSP’s, the neighbor continues to forward it throughout routing area

Flooding LSP’s to Neighbors (2) : Flooding LSP’s to Neighbors (2) LSPs are sent out under the following conditions -Initial router start up or routing process -When there is a change in topology

Step 5: Constructing a Link State Topology : Step 5: Constructing a Link State Topology Routers use a database to construct a topology map of the network Best path selected from topologyand placed in routing table

Sample Exchange of LSP’s : Sample Exchange of LSP’s

Shortest Path First (SPF) Tree : Shortest Path First (SPF) Tree Building a portion of the SPF tree Process begins by examining R2’s LSP information -R1 ignores 1st LSP Reason: R1 already knows it’s connected to R2

Shortest Path First (SPF) Tree : Shortest Path First (SPF) Tree Building a portion of the SPF tree -R1 uses 2nd LSP Reason: R1 can create a link from R2 to R5. This information is added to R1’s SPF tree

Shortest Path First (SPF) Tree : Shortest Path First (SPF) Tree Building a portion of the SPF tree -R1 uses 3rd LSP Reason: R1 learns that R2 is connected to 10.5.0.0/16. This link is added to R1’s SPF tree.

Link-State Routing Path Determination : Link-State Routing Path Determination Determining the shortest path The shortest path to a destination determined by adding the costs & finding the lowest cost

Link-State Routing Table : Link-State Routing Table Once the SPF algorithm has determined the shortest path routes, these routes are placed in the routing table.

Routing Protocols Comparison Table : Routing Protocols Comparison Table Advantages of a Link-State Routing Protocol

Link-State Hardware Requirements : Link-State Hardware Requirements Memory requirements Typically link state routing protocols use more memory Processing Requirements More CPU processing is required of link state routing protocols Bandwidth Requirements Initial startup of link state routing protocols can consume lots of bandwidth

Link State Routing Protocols : Link State Routing Protocols Two link state routing protocols used for routing IP -Open Shortest Path First (OSPF) -Intermediate System-Intermediate System (IS-IS)