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Chapter 08

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Chapter 08

  1. 1. CHAPTER EIGHT Routing Protocols
  2. 2. Objectives <ul><li>Differentiate between nonroutable, routed and routing protocols </li></ul><ul><li>Define Interior Gateway Protocols, Exterior Gateway Protocols, distance-vector routing protocols, and link-state routing protocols </li></ul><ul><li>Explain the concepts of count-to-infinity, split horizon, split horizon with poison reverse, and hold-down timers </li></ul><ul><li>Describe, configure, and monitor interior routing protocols RIP and IGRP </li></ul><ul><li>Explain static routing and administrative distance </li></ul><ul><li>Configure static routing and default routes </li></ul>
  3. 3. Nonroutable Protocols Figure 8-1: Early network model using coaxial cable
  4. 4. Nonroutable Protocols <ul><li>Peer-to-peer networks </li></ul><ul><ul><li>Small networks in which each computer can give and receive network services </li></ul></ul><ul><li>Nonroutable protocols </li></ul><ul><ul><li>Protocols that do not contain Network layer addressing and therefore can pass between multiple networks </li></ul></ul>
  5. 5. Routed Protocols <ul><li>Have packet headers that can contain Network layer addresses </li></ul><ul><li>Figure 8-2 shows a typical internetwork within which routed protocols are used </li></ul>Figure 8-2: Common internetwork
  6. 6. Routed Protocols <ul><li>Transmission Control Protocol/Internet Protocol (TCP/IP) </li></ul><ul><ul><li>Routed protocol stack developed in late 1960s for use on precursor to the Internet </li></ul></ul><ul><li>Internetwork Packet Exchange/Sequence Packet Exchange (IPX/SPX) </li></ul><ul><ul><li>Routed protocol stack developed by Novell for use with the Netware network operating system </li></ul></ul><ul><li>Logical addresses </li></ul><ul><ul><li>Layer 3 addresses that allow routed protocols to determine which network a particular host is on </li></ul></ul>
  7. 7. Routed Protocols Figure 8-3: Common internetwork with IP addresses
  8. 8. Routing Protocols <ul><li>Protocols used by routers to make path determination choices and to share those choices with other routers </li></ul>Table 8-1: Conceptual route table
  9. 9. Routing Protocols <ul><li>Hop count </li></ul><ul><ul><li>Number of routers a packet must pass through to reach a particular network </li></ul></ul><ul><li>A metric is a value used to define the suitability of a particular route </li></ul><ul><li>An autonomous system (AS) is a group of routers under the control of a single administration </li></ul>
  10. 10. Routing Protocols Figure 8-4: Big Tin Inc.’s AS
  11. 11. Routing Protocols <ul><li>Routing protocols come in two major categories: </li></ul><ul><ul><li>Interior Gateway Protocols (IGPs) </li></ul></ul><ul><ul><ul><li>Routing Information Protocol (RIP), Interior Gateway Routing Protocol (IGRP), Enhanced Interior Gateway Routing Protocol (EIGRP), and Open Shortest Path First (OSPF) are examples of IGPs </li></ul></ul></ul><ul><ul><li>Exterior Gateway Protocols (EGPs) </li></ul></ul><ul><ul><ul><li>Border Gateway Protocol (BGP) and Exterior Gateway Protocol are examples of EGPs </li></ul></ul></ul>
  12. 12. Types of IGP Routing Protocols: Distance-Vector Routing Protocols <ul><li>Broadcast their entire routing table to each neighbor router at predetermined intervals </li></ul>Figure 8-5: Distance-vector routing protocol process
  13. 13. Types of IGP Routing Protocols: Distance-Vector Routing Protocols <ul><li>Routing by rumor </li></ul><ul><ul><li>The learning of routes through second-hand information, and not directly from the router experiencing the change </li></ul></ul><ul><ul><li>One of the main problems with distance-vector routing protocols </li></ul></ul><ul><li>Convergence </li></ul><ul><ul><li>A state where all routers on the internetwork share a common view of the internetwork routes </li></ul></ul>
  14. 14. Types of IGP Routing Protocols: Distance-Vector Routing Protocols Figure 8-6: Distance-vector convergence example
  15. 15. Types of IGP Routing Protocols: Distance-Vector Routing Protocols <ul><li>Problems, such as routing loops, can occur with distance-vector protocols if control measures are not put in place </li></ul><ul><li>Routing loops </li></ul><ul><ul><li>Often referred to as count-to-infinity problems </li></ul></ul><ul><ul><li>Network state in which packets are continually forwarded from one router to another in an attempt to find the destination network </li></ul></ul>
  16. 16. Types of IGP Routing Protocols: Distance-Vector Routing Protocols Figure 8-7: Distance-vector convergence problems
  17. 17. Types of IGP Routing Protocols: Distance-Vector Routing Protocols <ul><li>Defining a maximum </li></ul><ul><ul><li>One of the easiest ways to limit count-to-infinity problems </li></ul></ul><ul><ul><li>Technique used with distance-vector routing protocols to prevent packets from bouncing infinitely throughout an internetwork </li></ul></ul><ul><ul><ul><li>If you assign a packet a maximum hop count, it cannot bounce infinitely around the internetwork </li></ul></ul></ul>
  18. 18. Types of IGP Routing Protocols: Distance-Vector Routing Protocols <ul><li>Two other common ways to prevent routing loops with distance-vector routing protocols: </li></ul><ul><ul><li>Split horizon </li></ul></ul><ul><ul><ul><li>A router will not send an update for a route via an interface from which it originally received knowledge of that route </li></ul></ul></ul><ul><ul><li>Split horizon with poison reverse </li></ul></ul><ul><ul><ul><li>A split horizon in which the router responds to attempts to updated a route with an update that marks the route in contention as unreachable </li></ul></ul></ul>
  19. 19. Types of IGP Routing Protocols: Distance-Vector Routing Protocols <ul><li>Hold-down timer </li></ul><ul><ul><li>Common technique used to stop routing loops </li></ul></ul><ul><ul><li>Allows a router to place a route in a state where it will not accept any changes to that route </li></ul></ul><ul><ul><li>Configurable by the network administrator </li></ul></ul><ul><ul><li>Can prevent improper route information from being propagated throughout the network </li></ul></ul>
  20. 20. Types of IGP Routing Protocols: Link-State Routing Protocols <ul><li>Routers configured with a link-state routing protocol use link-state advertisements (LSAs) to inform neighbor routers on the internetwork </li></ul><ul><ul><li>Instead of sending entire routing tables, LSAs contain only local links for the advertised router </li></ul></ul><ul><ul><li>The Shortest Path First (SPF) algorithm uses the link information to compute the routes </li></ul></ul><ul><ul><li>CPU resources are used instead of bandwidth </li></ul></ul>
  21. 21. Types of IGP Routing Protocols: Link-State Routing Protocols <ul><li>Link-state packets (LSPs) </li></ul><ul><ul><li>Allow every router in the internetwork to share a common view of the internetwork’s topology </li></ul></ul><ul><li>Flood </li></ul><ul><ul><li>Process of broadcasting packets onto a network </li></ul></ul><ul><li>Triggered updates </li></ul><ul><ul><li>Occur due to network topology changes </li></ul></ul>
  22. 22. Types of IGP Routing Protocols: Link-State Routing Protocols Figure 8-8: Link-state advertisements
  23. 23. Types of IGP Routing Protocols: Link-State Routing Protocols Table 8-2: Major characteristics of distance-vector and link-state routing protocols
  24. 24. Routing Information Protocol <ul><li>A distance-vector routing protocol </li></ul><ul><li>Has a maximum hop count of 15 </li></ul><ul><li>Hop count is the only metric available for path selection </li></ul><ul><li>Broadcasts entire routing table to neighbors every 30 seconds </li></ul><ul><li>Capable of load balancing </li></ul><ul><li>Easy to configure </li></ul>
  25. 25. Routing Information Protocol <ul><li>To install RIP on a Cisco router using TCP/IP, you must perform the following two tasks: </li></ul><ul><ul><li>Enable RIP </li></ul></ul><ul><ul><li>Configure RIP for each major network you wish to advertise </li></ul></ul><ul><li>You need only to configure major network numbers with RIP </li></ul><ul><ul><li>RIP does not maintain subnet mask information within routing tables it produces </li></ul></ul>
  26. 26. Enable RIP Routing Figure 8-9: Sample IP network
  27. 27. Configuring RIP Routing for Each Major Network Figure 8-10: Global configuration mode
  28. 28. Configuring RIP Routing for Each Major Network <ul><li>Administrative distance </li></ul><ul><ul><li>Value used to determine reliability of a particular route </li></ul></ul>Figure 8-11: Configuring RIP
  29. 29. Configuring RIP Routing for Each Major Network Figure 8-12: Output from the show ip route command
  30. 30. Configuring RIP Routing for Each Major Network Table 8-3: Administrative distances
  31. 31. Show IP Protocol and debug IP Rip Commands Figure 8-13: Output from the show ip protocol command
  32. 32. Show Ip Protocol and Debug Ip Rip Commands <ul><li>Flush interval </li></ul><ul><ul><li>The time at which a route will be totally removed from the routing table if no updates are received </li></ul></ul><ul><li>The debug ip rip command—like all debug commands—should only be used when troubleshooting RIP </li></ul>
  33. 33. Show Ip Protocol and Debug Ip Rip Commands Figure 8-14: Output from the debug ip rip command
  34. 34. Show Ip Protocol and Debug Ip Rip Commands Figure 8-15: Output from the show ip route command
  35. 35. Show Ip Protocol and Debug Ip Rip Commands Figure 8-16: New output from the show ip route command
  36. 36. Show Ip Protocol and Debug Ip Rip Commands Figure 8-17: RIP problems caused by hop count reliance
  37. 37. Interior Gateway Routing Protocol (IGRP) <ul><li>Proprietary distance-vector routing protocol created by Cisco </li></ul><ul><li>Solves some of the problems associated with RIP </li></ul><ul><li>A larger hop count allows IGRP to be used in larger networks </li></ul><ul><li>IGRP does not use hops as a metric by default </li></ul>
  38. 38. Interior Gateway Routing Protocol (IGRP) <ul><li>Metrics that can be configured for IGRP: </li></ul><ul><ul><li>Hops </li></ul></ul><ul><ul><li>Load </li></ul></ul><ul><ul><li>Bandwidth </li></ul></ul><ul><ul><li>Reliability </li></ul></ul><ul><ul><li>Delay </li></ul></ul><ul><ul><li>MTU </li></ul></ul>
  39. 39. Interior Gateway Routing Protocol (IGRP) Figure 8-18: Commands used to configure IGRP
  40. 40. Interior Gateway Routing Protocol (IGRP) Figure 8-19: The show ip route command with IGRP
  41. 41. Interior Gateway Routing Protocol (IGRP) Figure 8-20: The show ip protocol command with IGRP
  42. 42. Interior Gateway Routing Protocol (IGRP) Figure 8-21: Output from the debug ip igrp command
  43. 43. Static Routing <ul><li>Stub router </li></ul><ul><ul><li>Router with only one route </li></ul></ul><ul><li>Stub network </li></ul><ul><ul><li>Network with one route to the Internet </li></ul></ul><ul><li>Static route </li></ul><ul><ul><li>Route manually added by a network administrator to the routing table of a router </li></ul></ul>
  44. 44. Adding Static Routes Figure 8-22: Routing table for RouterC
  45. 45. Changing Administrative Distance <ul><li>IP route command also allows you to configure an administrative distance </li></ul><ul><li>Static routes have a much lower default metric than routes learned by dynamic routing protocols </li></ul><ul><ul><li>A static route is considered to be a preferred rout since someone took the trouble to enter it </li></ul></ul><ul><li>If you want the static route to be a back up route to one learned via a dynamic routing protocol, set the administrative distance of the static route higher than that of the default dynamic routing protocol </li></ul>
  46. 46. Configuring a Default Route <ul><li>Default route </li></ul><ul><ul><li>Static route that directs all traffic not specified anywhere else in the routing table to a particular route </li></ul></ul><ul><ul><li>Configured by the administrator </li></ul></ul><ul><ul><li>Sometimes called a quad zero route </li></ul></ul>
  47. 47. Configuring a Default Route Figure 8-23: Default route example
  48. 48. Chapter Summary <ul><li>Protocols vary in their functions </li></ul><ul><li>Nonroutable protocols are designed to be used in small networks without the need for Network layer addressing </li></ul><ul><li>Routed protocols were designed with the ability to move between multiple networks via Network layer addressing </li></ul><ul><li>Routing protocols are classed in two major groups: </li></ul><ul><ul><li>Interior Gateway Protocols </li></ul></ul><ul><ul><li>Exterior Gateway Protocols </li></ul></ul>
  49. 49. Chapter Summary <ul><li>Interior routing protocols are divided into distance-vector routing protocols and link-state routing protocols </li></ul><ul><li>Distance-vector protocols periodically broadcast entire routing tables to neighbor routers </li></ul><ul><li>Link-state protocols broadcast link updates to neighbor routers on the internetwork upon startup and when network topology changes </li></ul><ul><li>Two common distance-vector IGPs are RIP and IGRP </li></ul>
  50. 50. Chapter Summary <ul><li>RIP is an easy-to-configure routing protocol that uses hop count as its sole metric </li></ul><ul><li>IGRP is not limited to using hop counts as its sole metric </li></ul><ul><li>Static routes are used to conserve bandwidth and lower memory and CPU load on a router while still allowing for correct routing table creation </li></ul><ul><li>Static routes give administrators control and flexibility in path selection in a network </li></ul>

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