Routing & IGRP

1. Routing & IGRP Semester 3, Chapter 5 Allan Johnson

2. Go There! Go There! Go There! Go There! Table of Contents Network Layer Basics Routing & Routed Protocols IP Routing Protocols IGRP Operation

3. Table of Contents End Slide Show Network Layer Basics

4. Path Determination • A router’s main responsibility when routing packets is its path determination function. • Path determination is the process of making a forwarding decision? (At what layer?) • What do routers use to make a forwarding decision? What metric counts the number of routers the packet goes through? • What are the two parts of a routed protocol? • Which part do routers use to determine the path? • Once the router has determined the path, what function allows it to forward it out the correct interface?

5. Router’s Steps • Router operation has four basic steps: • Open the frame received on the interface and read the MAC address. • If the MAC resides on the same subnet, discard the frame. If the frame is an ARP request for a destination on a different subnet, reply with router’s MAC. All other broadcasts are discarded. If the IP specifies a host on another subnet, open the packet. • Read the IP address and look it up in the routing table. Use the routing protocol(s) configured to determine the best path. • Re-encapsulate the packet in the correct frame format with the next-hop’s data-link layer address and switch the frame out that interface

6. Table of Contents End Slide Show Routed & Routing Protocols

7. Routed Protocols • Routed protocols are moved across the network by routing protocols. • Each routed protocol has its own layer 3 packet header format with its own unique hierarchical addressing scheme. • What are some examples of routed protocols?

8. Routing Protocols • Routing protocols are used by routers to communicate with each other about various paths to the destination. • Each routing protocol has its own set of benefits and drawbacks. • What are some examples of routing protocols?

9. Multiprotocol Routing • Routers are capable of using multiple routed and routing protocols at the same time. • Through the use of subinterfaces, a router can even use different routed protocols on the same interface. (See Graphic)

10. Routed & Routing Review IP IPX Apple Interior Exterior Dist-V Link-S Hybrid EGP BGP RIP IGRP OSPF EIGRP

11. Table of Contents End Slide Show IP Routing Protocols

12. Primary Goals of Routing Protocols • Optimal Route—pick the best route • Efficiency—minimal use of bandwidth and router processor resources • Rapid Convergence—the faster, the better. Some are quicker at converging than others. • Flexibility—can handle a wide variety of situations such as high usage and failed routes

13. Interior vs. Exterior • Interior Routing protocols operated within an Autonomous System. What are some examples? • Exterior Routing protocols operated between an Autonomous System. What are some examples?

14. Interior Routing Protocols • Distance-Vector—passes periodic copies of its routing tables to its neighbor routers. How often for RIP? IGRP? • Link-State—broadcasts or multicasts topology changes when they occur. Also called SPF routing. SPF stands for….? • Hybrid—a distance-vector routing protocol that does not send periodic copies of its routing table. Instead, it sends topology change updates. What protocol is a hybrid?

15. Dynamic v. Static • Static routing is not a protocol. The net. admin. statically configures a route using the ip route command. • Dynamic routing refers to the use of a routing protocol to determine the path. In dynamic routing… • Routes are dynamically adjusted as the topology changes. • Accurate routing tables and timely updates are crucial to avoid routing loops and unacceptable delay. • A lack of convergence (all routers with the same information) is the main reason for inaccurate routing tables and routing loops. • Routing loops are solved through hold down timers, split horizons, and poison reverse routes. Describe each of these solutions.

16. Configuring Routing Protocols • Two steps: • Under global configuration mode… • Enable the routing protocol • Router(config)# router protocol [process-id] • [process-id]is the Autonomous System number for IGRP and EIGRP. For OSPF, it has a different meaning. • In router subconfiguration mode… • Add the directly connected network numbers • Router(config-router)# network A.B.C.D. • A.B.C.D.is the network address (e.g. 172.16.0.0)

17. Table of Contents End Slide Show IGRP Operation

18. IGRP Metrics • IGRP is a Cisco proprietary routing protocol that was developed to supercede RIP. • IGRP provides a wide range of configurable metrics. Net. Admin. can set values for… • Bandwidth--choose the fastest route. If two equal paths, then load balance • Delay--chose the route with the least amount of cumulative interface delay along the path • The following are not normally used because they cause more frequent routing table calculations. • Load--similar to delay, based upon total bits per second currently being transmitted (throughput) • Reliability--based on keepalives, chose the link that stays up the most • MTU--choose the link with the largest MTU • Hop Count--can be as high as 255 • By default, IGRP gives bandwidth the most important weight.

19. Configuring IGRP • Two steps: • Under global configuration mode… • Enable IGRP routing • Router(config)# router igrp 100 • 100 is the Autonomous System number. • In router subconfiguration mode… • Add the directly connected network numbers • Router(config-router)# network 172.16.0.0

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