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Giao thức định tuyến - Chapter 3

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Describe the role o dy a c routing pooco sad esc be e o e of dynamic ou g protocols and place these protocols in the context of modern network design. Identify several ways to classify routing protocols. Describe how metrics are used by routing protocols and identify the metric types used by dynamic routing protocols. Determine the administrative distance of a route and describe its importance in the routing process. Identify the different elements of the routing table.

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  1. Introduction to Dynamic Routing Protocol Routing Protocols and Concepts – Chapter 3 ITE PC v4.0 1 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
  2. Objectives Describe the role of dynamic routing protocols and esc dy place these protocols in the context of modern network design. Identify several ways to classify routing protocols. Describe how metrics are used by routing protocols Describe how metrics are used by routing protocols and identify the metric types used by dynamic routing protocols. Determine the administrative distance of a route and describe its importance in the routing process. Identify the different elements of the routing table. ITE PC v4.0 2 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
  3. Dynamic Routing Protocols Dynamic routing protocols are usually usua used in larger networks to ease the administrative and operational overhead of using only static routes. Typically, a network uses a combination of both a dynamic routing protocol and static routes. ITE PC v4.0 3 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
  4. The Evolution of Dynamic Routing Protocols One of the earliest routing protocols was Routing Information Protocol (RIP). –RIP has evolved into a newer version RIPv2. However, RIP –The newer version of RIP still does not scale to larger network implementations. To address the needs of larger networks, two advanced routing protocols were developed: Open Shortest Path First (OSPF) and Intermediate System-to- Intermediate System (IS-IS). (IS Cisco developed Interior Gateway Routing Protocol (IGRP) and Enhanced IGRP (EIGRP), which also scales well in larger network implementations. Additionally, there was the need to interconnect different internetworks and provide there was the need to interconnect different internetworks and provide routing among them. Border Gateway Routing (BGP) protocol is now used between ISPs as well as between ISPs and their larger private clients to exchange routing information. With the advent of numerous consumer devices using IP, the IPv4 addressing space the advent of numerous consumer devices using IP the IPv4 addressing space is nearly exhausted. Thus IPv6 has emerged. To support the communication based on IPv6, newer versions of the IP routing protocols have been developed (see the IPv6 row in the table). ITE PC v4.0 4 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
  5. Dynamic Routing Protocols Function(s) of Dynamic Routing Protocols: -Dynamically share information between routers. -Automatically update routing table when topology changes. -Determine best path to a destination. best path to destination –Compared to static routing, dynamic routing protocols require less administrative overhead. •However, the expense of using dynamic routing protocols is dedicating part of a router's the expense of using dynamic routing protocols is dedicating part of router resources for protocol operation including CPU time and network link bandwidth. – One of the primary benefits to using a dynamic routing protocol is that routers exchange routing information whenever there is a topology change. This exchange allows routers to automatically learn about new networks and also to find alternate ll fi paths when there is a link failure to a current network. ITE PC v4.0 5 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
  6. Dynamic Routing Protocols Despite the benefits of dynamic routing, static routing still esp be dy has its place. There are times when static routing is more appropriate and There are times when static routing is more appropriate and other times when dynamic routing is the better choice. More often than not you will find combination of both More often than not, you will find a combination of both types of routing in any network that has a moderate level of complexity. ITE PC v4.0 6 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
  7. Dynamic Routing Protocols A routing protocol –is a set of processes, algorithms, and messages that are used to exchange routing information and populate the routing table with the routing protocol's choice of best paths The purpose of a dynamic routing protocol is to: -Discover 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 fi th ITE PC v4.0 7 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
  8. Dynamic Routing Protocols Dynamic Routing Protocols Components of a routing protocol –Data structures structures •Some routing protocols use tables and/or databases for its operations. This information is kept in RAM –Algorithm •Algorithm is a finite list of steps used in accomplishing a task •Algorithms are used for facilitating routing information and best path are used for facilitating routing information and best path determination –Routing protocol messages •These are messages for discovering neighbors and exchange of di routing information , and other tasks to learn and maintain accurate information about the network. ITE PC v4.0 8 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
  9. Dynamic Routing Protocol Operation Dynamic Routing Protocol Operation All routing protocols have the same purpose - to learn about remote networks and to quickly adapt whenever there is a change in the topology. The method that a routing protocol uses to accomplish this depends upon the algorithm it uses and the operational characteristics of that protocol. In general, the operations of a dynamic routing protocol can be described as general the operations of dynamic routing protocol can be described as follows: –The router sends and receives routing messages on its interfaces. –The router shares routing messages and routing information with other routers that are using the same routing protocol. –Routers exchange routing information to learn about remote networks. –When a router detects a topology change the routing protocol can advertise this change to other routers. ITE PC v4.0 9 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
  10. Dynamic Routing Protocols of dynamic routing Advantages Advantages of static routing -It can backup multiple -Administrator has less work interfaces/networks on a router maintaining the configuration when -Minimal CPU processing adding or deleting networks. -Easier for administrator to for administrator to -Protocols automatically react to the understand topology changes. -Easy to configure -Configuration is less error-prone. -No extra resources are needed extra resources are needed -More scalable, growing the network -More secure usually does not present a problem Disadvantages of static routing Disadvantages of dynamic routing dynamic routing -Network changes require manual reconfiguration -Router resources are used (CPU -Configuration and maintenance is cycles, memory and link bandwidth). time time-consuming -More administrator knowledge is -Does not scale well in large required for configuration, topologies verification, and troubleshooting. -Configuration is error-prone, especially in large networks ITE PC v4.0 10 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
  11. Dynamic Routing Protocols ITE PC v4.0 11 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
  12. Classifying Routing Protocols Dynamic routing protocols are grouped according to characteristics. Examples include: -RIP -IGRP -EIGRP -OSPF -IS-IS -BGP Autonomous System is a group of routers under the control of a single authority. ITE PC v4.0 12 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
  13. Classifying Routing Protocols Dynamic routing protocols: –RIP •A distance vector interior routing protocol –IGRP •The distance vector interior routing developed by Cisco (deprecated from 12.2 IOS and later) –EIGRP •The advanced distance vector interior routing protocol developed by Cisco –OSPF •A link-state interior routing protocol –IS-IS •A link-state interior routing protocol –BGP •A path vector exterior routing protocol ITE PC v4.0 13 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
  14. Classifying Routing Protocols Classifying Routing Protocols An autonomous system (AS) - otherwise known as a routing domain - is a collection of routers under a common administration common administration. Because the Internet is based on the ASs concept, two types of routing protocols are required: interior and exterior routing protocols. -Interior Gateway Protocols (IGP) Interior Gateway Protocols •are used for intra-autonomous system routing - routing inside an autonomous system •IGPs are used for routing within a routing domain, those networks within the control of a single organization. –An autonomous system is commonly comprised of many individual networks belonging to companies, schools, and other institutions. • IGPs for IP include RIP, IGRP, EIGRP, OSPF, and IS-IS -Exterior Gateway Protocols (EGP) Gateway Protocols •are used for inter-autonomous system routing - routing between autonomous systems that are under the control of different administrations •At the ISP level, there are often more important issues the ISP level, there are often more important issues than just choosing the fastest path. •BGP is typically used between ISPs and sometimes between a company and an ISP ITE PC v4.0 14 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
  15. Autonomous systems An autonomous system (AS) is a collection of networks under common administration networks under a common administration sharing a common routing strategy. To the outside world, an AS is viewed as a single entity. The AS may be run by one or more operators while presenting a consistent view of routing to the external world. The American Registry of Internet Numbers (ARIN), a service provider, or an administrator assigns an identifying number to each AS. This autonomous system number is a 16 bit number. Routing protocols, such as Cisco’s IGRP, require assignment of a unique, autonomous system number. American Registry for Internet Numbers http://www.arin.net/registration/asn/index.html Autonomous System number (ASN) resource guide (ASN) http://www.apnic.net/services/asn_guide.html IS-IS ITE PC v4.0 15 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
  16. Autonomous systems Autonomous systems Cisco system AS number: http://ws.arin.net/cgi-bin/whois.pl ITE PC v4.0 16 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
  17. Autonomous systems Autonomous systems http://arin.net/education/asn_process/index.html RFC 1930 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 ITE PC v4.0 17 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
  18. Classifying Routing Protocols Classifying Routing Protocols IGP: Comparison of Distance 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 interface •Distance vector protocols typically use the Bellman- Ford algorithm for the best path route determination – incomplete view of network topology. 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. ITE PC v4.0 18 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
  19. Classifying Routing Protocols Classifying Routing Protocols IGP: Comparison of Distance Vector & Link State Link State Routing Protocols 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 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. ITE PC v4.0 19 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
  20. Classifying Routing Protocols Classifying Routing Protocols Comparison of Distance Vector & Link State Routing Protocols Di Distance vector protocols work Link-state protocols work best in best in situations where: situations where: –The network is simple and flat –The network design is hierarchical, and does not require a special usually occurring in large networks. hierarchical design. –The administrators have a good –The administrators do not have knowledge of the implemented link knowledge of the implemented link- enough knowledge to configure state routing protocol. and troubleshoot link-state –Fast convergence of the network is protocols. crucial crucial. –Specific types of networks, such as hub-and-spoke networks, are being implemented. –Worst-case convergence times in a network are not a concern. ITE PC v4.0 20 Chapter 1 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
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