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Week Ten

Week Ten. Attendance Announcements Data Center Design update Final exam 150 points Review Week Nine Information Current Week Information Upcoming Assignments Mimic Simulator Lab Assignment 4-1-2, Basic Routing and LAN Switching Configuration. Week Ten Topics. Routing Protocols

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Week Ten

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  1. Week Ten • Attendance • Announcements Data Center Design update Final exam 150 points • Review Week Nine Information • Current Week Information • Upcoming Assignments • Mimic Simulator Lab Assignment 4-1-2, Basic Routing and LAN Switching Configuration

  2. Week Ten Topics • Routing Protocols • Routing Table • Static versus dynamic routing • Interior Versus Exterior Routing Protocols • What is convergence? • Autonomous Systems • Definitions

  3. Routing Protocols • One of the primary jobs of a router is to determine the best path to a given destination • A router learns paths, or routes, from the staticconfiguration entered by an administrator or dynamically from other routers, through routing protocols

  4. Routing Table Principles Three principles regarding routing tables: • Every router makes its decisions alone, based on the information it has in its routing table. • Different routing table may contain different information • A routing table can tell how to get to a destination but not how to get back (Asymmetric Routing)

  5. Routing Table Objective • To forward a packet towards its destination network, which is the destination IP address of the packet. • To do this, a router needs to search the routing table for this stored information.

  6. Routing Tables • Routers keep a routing table in RAM • A routing table is a list of the best known available routes • Routers use this table to make decisions about how to forward a packet • On a Cisco router, the show IP route command is used to view the TCP/IP routing table • A routing table maps network prefixes to an outbound interface.

  7. Routing Table Specifics

  8. Routing Table • When RTA receives a packet destined for 192.168.4.46, it looks for the prefix 192.168.4.0/24 in the routing table • RTA then forwards the packet out an interface, such as Ethernet0, as directed in the routing table

  9. Routing Loops • A network problem in which packets continue to be routed in an endless circle • It is caused by a router or line failure, and the notification of the downed link has not yet reached all the other routers • It can also occur over time due to normal growth or when networks are merged together • Routing protocols utilize various techniques to lessen the chance of a routing loop

  10. Routing Table Specifics • Directly connected networks-this occurs when a device is connected to another router interface • Remotely connected networks-this is a network that is not directly connected to a particular router network/next hop associations-about the networks include source of information, network address & subnet mask, and Ip address of next-hop router • The show ip route command is used to view a routing table on a Cisco router

  11. Routing Table Specifics

  12. Routing Protocols • Directly Connected Routes-To visit a neighbor, you only have to go down the street on which you already live. This path is similar to a directly-connected route because the "destination" is available directly through your "connected interface," the street.

  13. Static Routing • Static Connected Routes-A train uses the same railroad tracks every time for a specified route. This path is similar to a static route because the path to the destination is always the same.

  14. Application For Static Routing • When network only consists of a few routers Using a dynamic routing protocol in such a case does not present any substantial benefit. • Network is connected to Internet only through one ISP There is no need to use a dynamic routing protocol across this link because the ISP represents the only exit point to the Internet

  15. Application For Static Routing • Static routing is not suitable for large, complex networks that include redundant links, multiple protocols, and meshed topologies Routers in complex networks must adapt to topology changes quickly and select the best route from multiple candidates • When an interface goes down, all static routes mapped to that interface are removed from the IP routing table

  16. Application For Static Routing • Hub and spoke topology is used on a large network A hub-and-spoke topology consists of a central location (the hub or switch) and multiple branch locations (spokes), with each spoke having only one connection to the hub or switch. Using dynamic routing would be unnecessary because each branch has only one path to a given destination-through the central location. • Static routing is useful in networks that have a single path to any destination network.

  17. Static Routes in Routing Table • Includes: network address and subnet mask and IP address of next hop router or exit interface • Denoted with the code S in the routing table • Routing tables must contain directly connected networks used to connect remote networks before static or dynamic routing can be used

  18. Static Routing

  19. Static Routing • The corporate network router has only one path to the network 172.24.4.0 connected to RTY • A static route is entered on RTZ

  20. Static Routing

  21. Routing Protocols • Dynamic Routes-When driving a car, you can "dynamically" choose a different path based on traffic, weather, or other conditions. This path is similar to a dynamic route because you can choose a new path at many different points on your way to the destination.

  22. Dynamic Routing Protocol • Are used to add remote networks to a routing table • Are used to discover networks • Are used to update and maintain routing tables

  23. Dynamic Routing Protocol • Automatic network discovery • Network discovery is the ability of a routing protocol to share information about the networks that it knows about with other routers that are also using the same routing protocol. • Dynamic routing protocols are used to share routing information with other routers and to maintain an up-to-date routing table. • Dynamic routing protocols not only make a best path determination to various networks, they will also determine a new best path if the initial path becomes unusable (or if the topology changes)

  24. Dynamic Routing Protocol

  25. Configuring Dynamic Routing Protocols • Dynamic routing of TCP/IP can be implemented using one or more protocols which are often grouped according to where they are used. • Routing protocols designed to work inside an autonomous system are categorized as interior gateway protocols (IGPs). • Protocols that work between autonomous systems are classified as exterior gateway protocols (EGPs). • Protocols can be further categorized as either distance vector or link-state routing protocols, depending on their method of operation.

  26. Interior Versus Exterior Routing Protocols An interior gateway protocol (IGP) is a routing protocol that is used within an autonomous system (AS). Two types of IGP. Distance-vector routing protocols each router does not possess information about the full network topology. It advertises its distances to other routers and receives similar advertisements from other routers. Using these routing advertisements each router populates its routing table. In the next advertisement cycle, a router advertises updated information from its routing table. This process continues until the routing tables of each router converge to stable values.

  27. Interior Versus Exterior Routing Protocols Distance-vector routing protocols make routing decisions based on hop-by-hop. A distance vector router’s understanding of the network is based on its neighbors definition of the topology, which could be referred to as routing by rumor. Route flapping is caused by pathological conditions (hardware errors, software errors, configuration errors, intermittent errors in communications links, unreliable connections, etc.) within the network which cause certain reach ability information to be repeatedly advertised and withdrawn.

  28. Interior Versus Exterior Routing Protocols In networks with distance vector routing protocols flapping routes can trigger routing updates with every state change. Cisco trigger updates are sent when these state changes occur. Traditionally, distance vector protocols do not send triggered updates.

  29. Interior Versus Exterior Routing Protocols Link-state routing protocols, each node possesses information about the complete network topology. Each node then independently calculates the best next hop from it for every possible destination in the network using local information of the topology. The collection of best next hops forms the routing table for the node. This contrasts with distance-vector routing protocols, which work by having each node share its routing table with its neighbors. In a link-state protocol, the only information passed between the nodes is information used to construct the connectivity maps.

  30. Routing Protocols • Interior routing protocols are designed for use in a network that is controlled by a single organization • RIPv1 RIPv2, EIGRP, OSPF and IS-IS are all Interior Gateway Protocols

  31. Link State Analogy • Each router has a map of the network • Each router looks at itself as the center of the topology • Compare this to a “you are here” map at the mall • The map is the same, but the perspective depends on where you are at the time You

  32. Link State Routing Protocol • The link-state algorithm is also known as Dijkstra's algorithm or as the shortest path first (SPF) algorithm • The link-state routing algorithm maintains a complex database of topology information • The link-state routing algorithm maintains full knowledge of distant routers and how they interconnect. They have a complete picture of the network

  33. Link State Analogy

  34. Distant Vector Versus Link State

  35. Exterior Gateway Routing Protocol An exterior routing protocol is designed for use between different networks that are under the control of different organizations • An exterior routing routes traffic between autonomous systems • These are typically used between ISPs or between a company and an ISP • BGPv4is the Exterior Gateway Protocol used by all ISPs on the Internet

  36. EGI and EGP Routing Protocol

  37. What is Convergence • Routers share information with each other, but must individually recalculate their own routing tables • For individual routing tables to be accurate, all routers must have a common view of the network topology • When all routers in a network agree on the topology they are considered to have converged

  38. Why is Quick Convergence Important? • When routers are in the process of convergence, the network is susceptible to routing problems because some routers learn that a link is down while others incorrectly believe that the link is still up • It is virtually impossible for all routers in a network to simultaneously detect a topology change.

  39. Convergence Issues Factors affecting the convergence time include the following: • Routing protocol used • Distance of the router, or the number of hops from the point of change • Number of routers in the network that use dynamic routing protocols • Bandwidth and traffic load on communications links • Load on the router • Traffic patterns in relation to the topology change

  40. What are Autonomous Systems? • An Autonomous System (AS) is a group of routers that share similar routing policies and operate within a single administrative domain. • An AS can be a collection of routers running a single IGP, or it can be a collection of routers running different protocols all belonging to one organization. • In either case, the outside world views the entire Autonomous System as a single entity.

  41. Autonomous System AS Numbers • Each AS has an identifying number that is assigned by an Internet registry or a service provider. • This number is between 1 and 65,535. • AS numbers within the range of 64,512 through 65,535are reserved for private use. • This is similar to RFC 1918 IP addresses. • Because of the finite number of available AS numbers, an organization must present justification of its need before it will be assigned an AS number. • An organization will usually be a part of the AS of their ISP

  42. Autonomous System

  43. Autonomous System • Each AS has its own set of rules and policies. • The AS number uniquely distinguish it from other ASs around the world.

  44. Definitions • Metric is a numeric value used by routing protocols to help determine the best path to a destination. RIP uses the metric hop count number . The lower the numeric value, the closer the destination. OSPF uses the metric bandwidth. EIGRP uses bandwidth and default

  45. Definitions • Flat routing protocol is when all routing information is spread through the entire network. • Hierarchical routing protocol are typically classless link-state protocols. This means that classless means that routing updates include subnet masks in their routing updates. Draw diagram • Administrative distance is the measure used by Cisco routers to select the best path when there are two or more different routes to the same destination from two different routing protocols. Administrative distance defines the reliability of a routing protocol. Each routing protocol is prioritized in order of most to least reliable (believable) using an administrative distance value. A lower numerical value is preferred.

  46. Administrative Distance

  47. EIGRP Characteristics EIGRP is an advanced distance vector protocol that employs the best features of link-state routing.

  48. OSPF Characteristics OSPF is the standardized protocol for routing IPv4. Since it’s initial development, OSPF has been revised to be implemented with the latest router protocols. • Developed for large networks (50 routers or more) • Must be a backbone area • Routers that operate on boundaries between the backbone and non-backbone are called, Arear Border Routers (ABR) • OSPF is a link state protocol

  49. OSPF Characteristics When the OSPF topology table is fully populated, the SPF algorithm calculates the shortest path to the destination. Triggered updates and metric calculation based on the cost of a specific link ensure quick selection of the shortest path to the destination.

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