Cisco Networking Academy Chapter 8: Routing Dynamically PDF

Chapter 8: Routing Dynamically Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 1  Chapter 8 8.1 Dynamic Routing Protocols 8.2 Distance Vector Dynamic Routing 8.3 RIP and RIPng Routing 8.4 Link-State...

Chapter 8: Routing Dynamically Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 1  Chapter 8 8.1 Dynamic Routing Protocols 8.2 Distance Vector Dynamic Routing 8.3 RIP and RIPng Routing 8.4 Link-State Dynamic Routing 8.5 The Routing Table 8.6 Summary Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 2  Chapter 8: Objectives  Explain the basic operation of dynamic routing protocols.  Compare and contrast dynamic and static routing.  Determine which networks are available during an initial network discovery phase.  Define the different categories of routing protocols.  Describe the process by which distance vector routing protocols learn about other networks.  Identify the types of distance-vector routing protocols.  Configure the RIP routing protocol.  Explain the process by which link-state routing protocols learn about other networks. Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 3  Chapter 8: Objectives (cont.)  Describe the information sent in a link-state update.  Describe advantages and disadvantages of using link-state routing protocols.  Identify protocols that use the link-state routing process. (OSPF, IS- IS)  Determine the route source, administrative distance, and metric for a given route.  Explain the concept of a parent/child relationship in a dynamically built routing table.  Compare the IPv4 classless route lookup process  Analyze a routing table to determine which route will be used to forward a packet. Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 4  Dynamic Routing Protocol Operation The Evolution of Dynamic Routing Protocols  Dynamic routing protocols used in networks since the late 1980s  Newer versions support the communication based on IPv6 Routing Protocols Classification Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 5  Dynamic Routing Protocol Operation Purpose of Dynamic Routing Protocols Routing Protocols are used to facilitate the exchange of routing information between routers. The purpose of dynamic routing protocols includes:  Discovery of remote networks  Maintaining up-to-date routing information  Choosing the best path to destination networks  Ability to find a new best path if the current path is no longer available Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 6  Dynamic Routing Protocol Operation Purpose of Dynamic Routing Protocols (cont.) Main components of dynamic routing protocols include:  Data structures - Routing protocols typically use tables or databases for its operations. This information is kept in RAM.  Routing protocol messages - Routing protocols use various types of messages to discover neighboring routers, exchange routing information, and other tasks to learn and maintain accurate information about the network.  Algorithm - Routing protocols use algorithms for facilitating routing information for best path determination. Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 7  Dynamic Routing Protocol Operation Purpose of Dynamic Routing Protocols (cont.) Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 8  Dynamic verses Static Routing Dynamic Routing Scorecard Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 9  Dynamic verses Static Routing Static Routing Scorecard Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 10  Routing Protocol Operating Fundamentals Dynamic Routing Protocol Operation In general, the operations of a dynamic routing protocol can be described as follows: 1. The router sends and receives routing messages on its interfaces. 2. The router shares routing messages and routing information with other routers that are using the same routing protocol. 3. Routers exchange routing information to learn about remote networks. 4. When a router detects a topology change the routing protocol can advertise this change to other routers. Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 11  Routing Protocol Operating Fundamentals  R1 adds the 10.1.0.0 Cold Start network available through interface FastEthernet 0/0 and 10.2.0.0 is available through interface Serial 0/0/0.  R2 adds the 10.2.0.0 network available through interface Serial 0/0/0 and 10.3.0.0 is available through interface Serial 0/0/1.  R3 adds the 10.3.0.0 network available through interface Serial 0/0/1 and 10.4.0.0 is available through Routers running RIPv2 interface FastEthernet 0/0. Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 12  Routing Protocol Operating Fundamentals Network Discovery R1:  Sends an update about network 10.1.0.0 out the Serial0/0/0 interface  Sends an update about network 10.2.0.0 out the FastEthernet0/0 interface  Receives update from R2 about network 10.3.0.0 with a metric of 1  Stores network 10.3.0.0 in the routing table with a metric of 1 Routers running RIPv2 Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 13  Routing Protocol Operating Fundamentals Network Discovery (cont.) R2:  Sends an update about network 10.3.0.0 out the Serial 0/0/0 interface  Sends an update about network 10.2.0.0 out the Serial 0/0/1 interface  Receives an update from R1 about network 10.1.0.0 with a metric of 1  Stores network 10.1.0.0 in the routing table with a metric of 1  Receives an update from R3 about network 10.4.0.0 with a metric of 1  Stores network 10.4.0.0 in the routing table with a Routers running RIPv2 metric of 1 Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 14  Routing Protocol Operating Fundamentals Network Discovery (cont.) R3:  Sends an update about network 10.4.0.0 out the Serial 0/0/1 interface  Sends an update about network 10.3.0.0 out the FastEthernet0/0  Receives an update from R2 about network 10.2.0.0 with a metric of 1  Stores network 10.2.0.0 in the routing table with a metric of 1 Routers running RIPv2 Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 15  Routing Protocol Operating Fundamentals Exchanging the Routing Information R1:  Sends an update about network 10. 1. 0. 0 out the Serial 0/0/0 interface  Sends an update about networks 10. 2. 0. 0 and 10. 3. 0. 0 out the FastEthernet0/0 interface  Receives an update from R2 about network 10. 4. 0. 0 with a metric of 2  Stores network 10. 4. 0. 0 in the routing table with a metric of 2  Same update from R2 contains information about network 10. 3. 0. 0 with a metric of 1. There is no Routers running RIPv2 change; therefore, the routing information remains the same Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 16  Routing Protocol Operating Fundamentals Exchanging the Routing Information (cont.) R2:  Sends an update about networks 10. 3. 0. 0 and 10. 4. 0. 0 out of Serial 0/0/0 interface  Sends an update about networks 10. 1. 0. 0 and 10. 2. 0. 0 out of Serial 0/0/1 interface  Receives an update from R1 about network 10. 1. 0. 0. There is no change; therefore, the routing information remains the same.  Receives an update from R3 Routers running RIPv2 about network 10. 4. 0. 0. There is no change; therefore, the routing information remains the Presentation_ID same. © 2008 Cisco Systems, Inc. All rights reserved. 17 Cisco Confidential  Routing Protocol Operating Fundamentals Exchanging the Routing Information (cont.) R3:  Sends an update about network 10. 4. 0. 0 out the Serial 0/0/1 interface  Sends an update about networks 10. 2. 0. 0 and 10. 3. 0. 0 out the FastEthernet0/0 interface  Receives an update from R2 about network 10. 1. 0. 0 with a metric of 2  Stores network 10. 1. 0. 0 in the routing table with a metric of 2  Same update from R2 contains information about Routers running RIPv2 network 10. 2. 0. 0 with a metric of 1. There is no change; therefore, the routing information remains Presentation_ID the same. © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 18  Routing Protocol Operating Fundamentals Achieving Convergence The network is converged when all routers have complete and accurate information about the entire network:  Convergence time is the time it takes routers to share information, calculate best paths, and update their routing tables.  A network is not completely operable until the network has converged.  Convergence properties include the speed of propagation of routing information and the calculation of optimal paths. The speed of propagation refers to the amount of time it takes for routers within the network to forward routing information.  Generally, older protocols, such as RIP, are slow to converge, whereas modern protocols, such as EIGRP and OSPF, converge more quickly. Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 19  Types of Routing Protocols Classifying Routing Protocols Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 20  Types of Routing Protocols IGP and EGP Routing Protocols Interior Gateway Protocols (IGP) -  Used for routing within an AS  Include RIP, EIGRP, OSPF, and IS-IS Exterior Gateway Protocols (EGP) -  Used for routing between AS  Official routing protocol used by the Internet Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 21  Types of Routing Protocols Distance Vector Routing Protocols Distance vector IPv4 IGPs:  RIPv1 - First generation legacy protocol  RIPv2 - Simple distance vector routing protocol  IGRP - First generation Cisco proprietary protocol (obsolete)  EIGRP - Advanced version of distance vector routing For R1, 172.16.3.0/24 is one hop away (distance). It can be reached through R2 (vector). Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 22  Types of Routing Protocols Distance Vector or Link-State Routing Protocols Distance vector protocols use routers as sign posts along the path to the final destination. A link-state routing protocol is like having a complete map of the network topology. 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. A link-state router uses the link-state information to create a topology map and to select the best path to all destination networks in the topology. Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 23  Types of Routing Protocols Link-State Routing Protocols Link-state IPv4 IGPs:  OSPF - Popular standards based routing protocol  IS-IS - Popular in provider networks. Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 24  Types of Routing Protocols Classful Routing Protocols Classful routing protocols do not send subnet mask information in their routing updates:  Only RIPv1 and IGRP are classful.  Created when network addresses were allocated based on classes (class A, B, or C).  Cannot provide variable length subnet masks (VLSMs) and classless interdomain routing (CIDR).  Create problems in discontiguous networks. Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 25  Types of Routing Protocols Classless Routing Protocols Classless routing protocols include subnet mask information in the routing updates:  RIPv2, EIGRP, OSPF, and IS_IS  Support VLSM and CIDR  IPv6 routing protocols Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 26  Types of Routing Protocols Routing Protocol Characteristics Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 27  Types of Routing Protocols Routing Protocol Metrics A metric is a measurable value that is assigned by the routing protocol to different routes based on the usefulness of that route:  Used to determine the overall “cost” of a path from source to destination.  Routing protocols determine the best path based on the route with the lowest cost. Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 28  Distance Vector Routing Protocol Operation Distance Vector Technologies Distance vector routing protocols:  Share updates between neighbors  Not aware of the network topology  Some send periodic updates to broadcast IP 255.255.255.255 even if topology has not changed  Updates consume bandwidth and network device CPU resources  RIPv2 and EIGRP use multicast addresses  EIGRP will only send an update when topology has changed Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 29  Distance Vector Routing Protocol Operation Distance Vector Algorithm RIP uses the Bellman-Ford algorithm as its routing algorithm. IGRP and EIGRP use the Diffusing Update Algorithm (DUAL) routing algorithm developed by Cisco. Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 30  Types of Distance Vector Routing Protocols Routing Information Protocol Routing Updates updates use broadcasted UDP every 30 port 520 seconds RIPng is based on RIPv2 with a 15 hop limitation and the administrative distance of 120 Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 31  Types of Distance Vector Routing Protocols Enhanced Interior-Gateway Routing Protocol EIGRP:  Is bounded triggered updates  Uses a Hello keepalives mechanism  Maintains a topology table  Supports rapid convergence  Is a multiple network layer protocol support Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 32  Configuring the RIP Protocol Router RIP Configuration Mode Advertising Networks Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 33  Configuring the RIP Protocol Examining Default RIP Settings Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 34  Configuring the RIP Protocol Enabling RIPv2 Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 35  Configuring the RIP Protocol Disabling Auto Summarization  Similarly to RIPv1, RIPv2 automatically summarizes networks at major network boundaries by default.  To modify the default RIPv2 behavior of automatic summarization, use the no auto-summary router configuration mode command.  This command has no effect when using RIPv1.  When automatic summarization has been disabled, RIPv2 no longer summarizes networks to their classful address at boundary routers. RIPv2 now includes all subnets and their appropriate masks in its routing updates.  The show ip protocols now states that automatic network summarization is not in effect. Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 36  Configuring the RIP Protocol Configuring Passive Interfaces Sending out unneeded updates on a LAN impacts the network in three ways:  Wasted Bandwidth  Wasted Resources  Security Risk Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 37  Configuring the RIP Protocol Propagating a Default Route Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 38  Link-State Routing Protocol Operation Shortest Path First Protocols Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 39  Link-State Routing Protocol Operation Dijkstra’s Algorithm Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 40  Link-State Updates Link-State Routing Process Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 41  Link-State Updates Link and Link-State The first step in the link-state routing process is that each router learns about its own links and its own directly connected networks. Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 42  Link-State Updates Say Hello The second step in the link-state routing process is that each router is responsible for meeting its neighbors on directly connected networks. Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 43  Link-State Updates Say Hello The third step in the link-state routing process is that each router builds a link-state packet (LSP) containing the state of each directly connected link. 1. R1; Ethernet network 10.1.0.0/16; Cost 2 2. R1 -> R2; Serial point-to- point network; 10.2.0.0/16; Cost 20 3. R1 -> R3; Serial point-to- point network; 10.7.0.0/16; Cost 5 4. R1 -> R4; Serial point-to- point network; 10.4.0.0/16; Cost 20 Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 44  Link-State Updates Flooding the LSP The fourth step in the link-state routing process is that each router floods the LSP to all neighbors, who then store all LSPs received in a database. Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 45  Link-State Updates Building the Link-State Database The final step in the link-state routing process is that each router uses the database to construct a complete map of the topology and computes the best path to each destination network. Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 46  Link-State Updates Building the SPF Tree Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 47  Link-State Updates Building the SPF Tree Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 48  Link-State Updates Adding OSPF Routes to the Routing Table Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 49  Why Use Link-State Routing Protocols Why Use Link-State Protocols? Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 50  Why Use Link-State Routing Protocols Why Use Link-State Protocols? Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 51  Why Use Link-State Routing Protocols Disadvantages of Link-State Protocols Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 52  Why Use Link-State Routing Protocols Protocols that Use Link-State There are only two link-state routing protocols:  Open Shortest Path First (OSPF) most popular began in 1987 two current versions OSPFv2 - OSPF for IPv4 networks OSPFv3 - OSPF for IPv6 networks  IS-IS was designed by International Organization for Standardization (ISO ) Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 53  Parts of an IPv4 Route Entry Routing Table Entries Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 54  Parts of an IPv4 Route Entry Directly Connected Entries Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 55  Parts of an IPv4 Route Entry Remote Network Entries Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 56  Chapter 8: Summary Dynamic routing protocols:  Used by routers to automatically learn about remote networks from other routers  Purpose includes: discovery of remote networks, maintaining up-to- date routing information, choosing the best path to destination networks, and ability to find a new best path if the current path is no longer available  Best choice for large networks but static routing is better for stub networks.  Function to inform other routers about changes  Can be classified as either classful or classless, distance-vector or link-state, and an interior or an exterior gateway protocol Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 57  Chapter 8: Summary (cont.) Dynamic routing protocols:  A link-state routing protocol can create a complete view or topology of the network by gathering information from all of the other routers  Metrics are used to determine the best path or shortest path to reach a destination network  Different routing protocols may use different (hops, bandwidth, delay, reliability, and load)  Show ip protocols command displays the IPv4 routing protocol settings currently configured on the router, for IPv6, use show ipv6 protocols Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 58  Chapter 8: Summary (cont.) Dynamic routing protocols:  Cisco routers use the administrative distance value to determine which routing source to use  Each dynamic routing protocol has a unique administrative value, along with static routes and directly connected networks, lower is preferred the route  Directly connected networks are preferred source, followed by static routes and then various dynamic routing protocols  An OSPF link is an interface on a router, information about the state of the links is known as link-states  Link-state routing protocols apply Dijkstra’s algorithm to calculate the best path route which uses accumulated costs along each path, from source to destination, to determine the total cost of a route Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 59 Presentation_ID © 2008 Cisco Systems, Inc. All rights reserved. Cisco Confidential 60