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Dynamic Routing

Dynamic Routing. CCNA Exploration Semester 2 Chapter 3 . Topics. Dynamic routing protocols and network design Classifying routing protocols Metrics Administrative distance Routing tables Subnetting. Routing protocols. Exterior gateway protocols Between ISPs, between ISP and major client

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Dynamic Routing

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  1. Dynamic Routing CCNA Exploration Semester 2 Chapter 3 S Ward Abingdon and Witney College

  2. Topics • Dynamic routing protocols and network design • Classifying routing protocols • Metrics • Administrative distance • Routing tables • Subnetting S Ward Abingdon and Witney College

  3. Routing protocols • Exterior gateway protocolsBetween ISPs, between ISP and major client • Path vector • BGP (border gateway protocol), EGP • Interior gateway protocolsWithin private groups of networks • Distance vector • RIPv1 and 2, (IGRP), EIGRP • Link state • OSPF, IS-IS S Ward Abingdon and Witney College

  4. Routing protocols Interior gateway protocols Exterior gateway protocols Classful Classless IPv6 S Ward Abingdon and Witney College

  5. Routing protocols Interior gateway protocols Exterior gateway protocols Classful Classless IPv6 Distance vector, open standard S Ward Abingdon and Witney College

  6. Routing protocols Interior gateway protocols Exterior gateway protocols Classful Classless IPv6 Distance vector, Cisco proprietary S Ward Abingdon and Witney College

  7. Routing protocols Interior gateway protocols Exterior gateway protocols Classful Classless IPv6 Link state S Ward Abingdon and Witney College

  8. Routing protocol - purpose • Purpose is to add dynamic routes to a router’s routing table. • They let routers exchange information about routes. • They choose the best route to each known destination and put it in the routing table. S Ward Abingdon and Witney College

  9. Static Dynamic • Requires knowledge to configure efficiently • CPU processing and memory used • Uses bandwidth • Adjusts automatically to topology changes • Less prone to error • Scales well to large networks • Less secure • Easy to understand and configure • Little CPU processing. • Uses no bandwidth • Needs re-configuring when topology changes • Prone to error in configuring • Does not scale well to large networks • More secure S Ward Abingdon and Witney College

  10. Autonomous systems • An autonomous system (AS) is a collection of networks under a common administration sharing a common routing strategy. • Also known as a routing domain. • Each AS has a 16 bit autonomous system number. • Interior gateway protocol used within an AS, Exterior gateway protocol between them. S Ward Abingdon and Witney College

  11. Autonomous systems • Autonomous systems divide up the global internetwork into manageable units S Ward Abingdon and Witney College

  12. Autonomous systems RFC 1930 • http://arin.net/education/asn_process/index.html • AS just like IP, it needs to apply from ARIN or the appropriate region and be unique on the internet. • The Internet Assigned Numbers Authority (IANA) has reserved the following block of AS numbers for private use (not to be advertised on the global Internet): 64512 through 65535

  13. Interior and Exterior BGP used between BGP used between RIP in AS 62 EIGRP in AS 36 OSPF in AS 98 S Ward Abingdon and Witney College

  14. Types of interior routing protocol • There are two main types of interior routing protocol • Distance Vector • Link State (Shortest Path First) • They work in different ways but they have the same purposes • Discover routes and put the best ones in the routing table • Remove routes that are no longer available S Ward Abingdon and Witney College

  15. Distance vector • A distance vector protocol learns: • The distance to a network, measured in hops or in some other way • The direction of the network: which port should be used to reach it • It puts the routes in the routing table • It does not know any more details of the route or the other routers along the way S Ward Abingdon and Witney College

  16. Distance vector Network 192.168.48.0 is 3 hops away using port fa0/0 Network 192.168.22.0 is 2 hops away using port fa0/0 S Ward Abingdon and Witney College

  17. Distance vector • Distance vector protocols typically use the Bellman-Ford algorithm for the best path route determination. • EIGRP uses the DUAL algorithm. • Some distance vector protocols send complete routing tables to all connected neighbors at intervals. • This can cause significant traffic on the links. S Ward Abingdon and Witney College

  18. Distance vector • Suitable for simple “flat” networks without hierarchical design. • Suitable for hub-and-spoke networks. • Easier to configure and troubleshoot than link-state protocols. • Slower to converge than link state. • Typically use more bandwidth but need less processing power than link state. S Ward Abingdon and Witney College

  19. Classifying Routing Protocols • IGP: Comparison ofDistance Vector & Link State Routing Protocols • Distance vector • routes are advertised as vectors of distance & direction. • Distance is defined in terms of a metric such as hop count (RIP) • Direction is simply the next-hop router or exit interface • Distance vector protocols typically use the Bellman-Ford algorithm for the best path route determination • incomplete view of network topology. • Distance vector protocols use routers as sign posts along the path to the final destination. • Distance vector routing protocols do not have an actual map of the network topology • Generally, periodic updates. • Some distance vector protocols periodically send complete routing tables to all connected neighbors.

  20. Link state • A link state routing protocol finds out about all the routers in the system and the networks they link to. • It builds up a complete picture of the topology • It can then work out the best path to any network • It puts these best paths in the routing table S Ward Abingdon and Witney College

  21. Link state I know all the routers and paths in this system of networks. S Ward Abingdon and Witney College

  22. Link state • Link-state routing protocols do not send periodic updates of whole routing tables. • After the network has converged, a link-state update only sent when there is a change in the topology. • All the routers have the same “map” of the network and each router works out its own best routes. S Ward Abingdon and Witney College

  23. Link state • Link-state protocols are suitable for large networks with hierarchical designs. • They can be difficult to configure efficiently: the administrators need a good knowledge of the protocol. • They provide fast convergence. • OSPF uses the Open Shortest Path First or Dijkstra algorithm

  24. Classifying Routing Protocols • IGP: Comparison ofDistance Vector & Link State Routing Protocols • Link state • complete view of network topology is created. • The sign posts along the way from source to destination are not necessary, because all link-state routers are using an identical "map" of the network. • updates are not periodic. • After the network has converged, a link-state update only sent when there is a change in the topology.

  25. Classifying Routing Protocols • Distance vector protocols work best in situations where: • The network is simple and flat and does not require a special hierarchical design. • The administrators do not have enough knowledge to configure and troubleshoot link-state protocols. • Specific types of networks, such as hub-and-spoke networks, are being implemented. • Worst-case convergence times in a network are not a concern. • Link-state protocols work best in situations where: • The network design is hierarchical, usually occurring in large networks. • The administrators have a good knowledge of the implemented link-state routing protocol. • Fast convergence of the network is crucial. • Comparison ofDistance Vector & Link State Routing Protocols

  26. Distance vector RIP v 1 and 2 IGRP EIGRP Link state OSPF IS-IS Types of routing protocol Not typical distance vector. Has some characteristics of link state. S Ward Abingdon and Witney College

  27. Classful routing protocols • IP addresses were based on classes. • Class A has subnet mask 255.0.0.0first octet 1 to 126 • Class B has subnet mask 255.255.0.0first octet 128 to 191 • Class C has subnet mask 255.255.255.0first octet 192 to 223 S Ward Abingdon and Witney College

  28. Classful routing protocols • Classful routing protocols do not send subnet masks in updates. There was no need because subnet masks were known from the first octet of the address. • They could be used with traditional subnetting where all subnets had the same mask. They do not support VLSM. • RIP v1 and IGRP are classful. S Ward Abingdon and Witney College

  29. Classless routing protocols • Modern addressing does not keep strictly to classes, so a knowledge of subnet masks is important. • Classless routing protocols exchange subnet masks in updates. • They support VLSM and CIDR • RIP v2 and EIGRP and OSPF are classless,so are IS-IS and BGP S Ward Abingdon and Witney College

  30. Convergence • In a converged network, all routers have up-to-date, accurate information and their routing tables are consistent. (But not the same.) • Networks are not properly operational until they have converged. • RIP and IGRP, traditional distance vector routing protocols, are slow to converge • Link state such as OSPF are faster. • EIGRP is also faster to converge. S Ward Abingdon and Witney College

  31. Classifying Routing Protocols • Convergence is defined as when all routers’ routing tables are at a state of consistency • The network has converged when all routers have complete and accurate information about the network • Convergence time is the time it takes routers to share information, calculate best paths, and update their routing tables. • Routing protocols can be rated based on the speed to convergence; the faster the convergence, the better the routing protocol. • RIP and IGRP are slow to converge • EIGRP and OSPF are faster to converge.

  32. Metrics • Routing protocols may find several routes to the same destination • They need to choose the best route • They use metrics (measurements) • The simplest metric is hop count • Other metrics are bandwidth, delay, load, reliability, cost S Ward Abingdon and Witney College

  33. Hop count as a metric • Used by RIP (Maximum 15 hop counts) • Easy to understand – the number of routers that the message must pass through • May not be the best route – there might be a faster route with more hops. • R 192.168.8.0/24 [120/2] via 192.168.4.1, 00:00:26, Serial0/0/1 metric S Ward Abingdon and Witney College

  34. Other metrics • IGRP and EIGRP: Bandwidth and Delay by default. Can use Reliability, and Load too. Formula to combine these and give metric. • OSPF: “Cost” – calculated from bandwidth in Cisco implementation. Higher bandwidth, lower cost. S Ward Abingdon and Witney College

  35. Load balancing • Routing table lists two routes to the same destination, with the same metric. • Both routes were discovered by the same protocol. • Both routes will be used. R 192.168.6.0/24 [120/1] via 192.168.2.1, 00:00:24, Serial0/0/0 [120/1] via 192.168.4.1, 00:00:26, Serial0/0/1 S Ward Abingdon and Witney College

  36. Administrative distance • Different routes could be found by different routing protocols, or one route could be dynamic and one static. • The route with the lowest administrative distance is used. • Administrative distance is an indication of the “trustworthiness” or desirability of a route. S Ward Abingdon and Witney College

  37. Administrative distances • 0 directly connected • 1 static route • 90 route found using EIGRP • 100 route found using IGRP • 110 route found using OSPF • 120 route found using RIP • Maximum possible value is 255 • These are default values. S Ward Abingdon and Witney College

  38. Administrative distance D 192.168.6.0/24 [90/2172416] via 192.168.2.1, 00:00:24, Serial0/0 R 192.168.8.0/24 [120/1] via 192.168.3.1, 00:00:20, Serial0/1 • Two routing protocols running on a router linking two areas with the different protocols • Administrative distances are the defaults for the routing protocols. • D means EIGRP. Note the metric is not hop count. S Ward Abingdon and Witney College

  39. Administrative Distance of a Route • In fact, a router might learn of a route to the same network from more than one source. • For example, a static route might have been configured for the same network/subnet mask that was learned dynamically by a dynamic routing protocol, such as RIP. The router must choose which route to install. • Purpose of a metric • It’s a calculated value used to determine the best path to a destination • Purpose of Administrative Distance • It’s a numeric value that specifies the preference of a particular route source. For equal cost routes to be installed they both must be static routes or they both must be RIP routes.

  40. Show ip rip database • Command shows all routes discovered by RIP, whether or not they go into the routing table. S Ward Abingdon and Witney College

  41. Show ip protocols • Information and statistics about all routing protocols that are running. S Ward Abingdon and Witney College

  42. Show ip route [route] • E.g. show ip route 192.168.1.0 • This gives additional information such as administrative distance for directly connected routes (0) or for static routes where the exit interface is given (1). S Ward Abingdon and Witney College

  43. Administrative Distance of a Route • The AD value can also be verified with the show ip protocols command.

  44. Administrative Distance of a Route • Directly connected routes • -Immediately appear in the routing table as soon as the interface is configured

  45. Administrative Distance of a Route • Directly connected routes • Have a default AD of 0 • Static Routes • Administrative distance of a static route has a default value of 1 • A static route using either a next-hop IP address or an exit interface has a default AD value of 1. • However, the AD value is not listed in show ip route when you configure a static route with the exit interface specified. When a static route is configured with an exit interface, the output shows the network as directly connected via that interface.

  46. Administrative Distance of a Route

  47. Summary • Dynamic routing protocols fulfill the following functions • -Dynamically share information between routers • -Automatically update routing table when topology changes • -Determine best path to a destination • Routing protocols are grouped as either • -Interior gateway protocols (IGP)Or • -Exterior gateway protocols(EGP) • Types of IGPs include • -Classless routing protocols - these protocols include subnet mask in routing updates • -Classful routing protocols - these protocols do not include subnet mask in routing update

  48. Summary • Metrics are used by dynamic routing protocols to calculate the best path to a destination. • Administrative distance is an integer value that is used to indicate a router’s “trustworthiness” • Components of a routing table include: • -Route source • -Administrative distance (The smaller the better) • -Metric (The smaller the better)

  49. Subnetting • Keep revising and practising. S Ward Abingdon and Witney College

  50. The End S Ward Abingdon and Witney College

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