Guide to TCP/IP, Third Edition. Chapter 10: Routing in the IP Environment

Transcription

1 Guide to TCP/IP, Third Edition Chapter 10: Routing in the IP Environment

2 Objectives Understand how basic routing works Describe various routing characteristics Understand interior gateway protocols, such as RIP, OSPF, and EIGRP Understand BGP, an exterior gateway protocol Describe how to manage routing on an in-house internetwork Routing in the IP Environment 2

3 Objectives (continued) Be aware of the challenges associated with redistributing a network from a classless protocol to a class-oriented protocol Describe factors involved in choosing a routing protocol for your wide area network Describe router connections on internal and external networks, including the Internet Routing in the IP Environment 3

4 Objectives (continued) Understand the importance of securing routers and routing protocols Explain basic router diagnostic troubleshooting concepts, tools, and techniques Routing in the IP Environment 4

5 Understanding Routing Routing table Database that lives in the memory of the router Compilation of information about all the networks that the router can reach Routing in the IP Environment 5

6 Routing in the IP Environment 6

7 How Entries Are Placed in the Routing Table Route entry can be placed in a routing table in three basic ways Through direct connection It can be manually configured An entry can be placed in a routing table is dynamically, by using a routing protocol Routing in the IP Environment 7

8 Routing Protocols and Routed Routing protocols Protocols Used to exchange routing information Routing Information Protocol (RIP) and OSPF are routing protocols Routed protocols Layer 3 protocols that are used to get packets through an internetwork Routing in the IP Environment 8

9 Grouping Routing Protocols Interior gateway protocols (IGPs) Routing protocols used inside a routing domain are called interior Exterior gateway protocols (EGPs) Routing protocols used to connect these routing domains Distance vector and link-state Used to communicate Routing in the IP Environment 9

10 Distance Vector Routing Protocols RIP Interior Gateway Routing Protocol (IGRP) Border Gateway Protocol (BGP) also is a distance vector routing protocol Routing in the IP Environment 10

11 Routing in the IP Environment 11

12 Link-State Routing Protocols Differ from distance vector routing protocols in two ways They do not route by rumor They do not periodically broadcast their entire tables Routing in the IP Environment 12

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14 Routing Characteristics Network Converged when all the routers know a loop-free path to get to all other networks Ideally should be in a converged state Split horizon Used to speed up the process of convergence and resolve the counting-to-infinity problem Poison reverse Technique for assigning costs to routes designed to prevent routing loops Routing in the IP Environment 14

15 Routing in the IP Environment 15

16 Routing Characteristics (continued) Time to Live Ensures that packets cannot loop endlessly through a network Defined in the Network layer header Multicast Versus Broadcast Update Behavior Routers can be configured to forward multicasts RIPv1 sends broadcast updates RIPv2 can send multicast updates Routing in the IP Environment 16

17 ICMP Router Advertisements Some routers Can be configured to send periodic ICMP Router Advertisement packets Periodic ICMP Router Advertisements Allow hosts to learn passively about available routes Unsolicited ICMP Router Advertisements Sent periodically to the all-hosts multicast address Routing in the IP Environment 17

18 Black Holes Occurs on a network when ICMP is turned off and Router discards packets without sending any notification about its actions Routing in the IP Environment 18

19 Routing in the IP Environment 19

20 Areas, Autonomous Systems, and OSPF utilizes areas Border Routers To reduce the number of entries in the link-state database OSPF specification Defines the need for a backbone area, Area 0 Autonomous systems (ASs) Groups of routers under a single administrative authority Routing in the IP Environment 20

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23 Interior Gateway Protocols Used to exchange routing information within an AS Also are referred to as intra-domain routing protocols RIP Basic distance vector routing protocol Two versions: RIPv1 and RIPv2 Communications are UDP based RIP-based routers send and receive datagrams on UDP port number 520 Routing in the IP Environment 23

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27 Open Shortest Path First Defined in RFC 2328 The premier link-state routing protocol used on TCP/IP networks Based on Configurable values (metrics) that may be based on network bandwidth, delay, or monetary cost Routing in the IP Environment 27

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29 Open Shortest Path First (continued) Six basic types of LSAs: Type 1 (Router Links Advertisement) Type 2 (Network Links Advertisement) Type 3 (Network Summary Link Advertisement) Type 4 (AS Boundary Router Summary Link Advertisement) Type 5 (AS External Link Advertisement) Type 7 (Not So Stubby Area Networks Advertisement) Routing in the IP Environment 29

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32 Enhanced Interior Gateway Routing Protocol Interior Gateway Routing Protocol (IGRP) Developed in the 1980s by Cisco Systems Updated in the early 1990s (Enhanced Interior Gateway Routing Protocol) Enhanced Interior Gateway Routing Protocol Integrates the capabilities of link-state routing into a distance vector routing protocol Routing in the IP Environment 32

33 Border Gateway Protocol Exterior gateway protocols (EGP) Used to exchange routing information between separate autonomous systems Defined in RFC 904 Border Gateway Protocol (BGP) replaces EGP routing Routing in the IP Environment 33

34 Border Gateway Protocol (continued) Offers three types of routing operations Inter-autonomous system routing Intra-autonomous system routing Pass-through autonomous system routing When configured for intra-autonomous system routing BGP routers are located within the same AS Pass-through autonomous system routing Enables BGP peer routers to exchange routing information across an AS that does not support BGP Routing in the IP Environment 34

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36 Managing Routing on an In-House Internetwork IP routing protocols have a shortcoming They do not discriminate between users, types of traffic, and so on They only know how to get to a network Policy-based routing addresses this shortcoming Routing in the IP Environment 36

37 Hybrid Networks What happens when you redistribute a network from a classless protocol to a class-oriented protocol that only understands the major network address but not the VLSM you re using? How can you convert the bandwidth, delay, load, reliability, and MTU size of EIGRP and IGRP into the simple hop counts that RIP uses? Routing in the IP Environment 37

38 Routing On and Off a Wide Area Network If the network in question is relatively small Consider using no routing protocol Frame relay and ATM Use virtual circuits So one physical interface can actually be logically partitioned into several logical interfaces. If your company also uses Novell s IPX protocol You may have to run one routing protocol for IP and another routing protocol for IPX Routing in the IP Environment 38

39 Mobile Users Mobile IP Defined by the IETF in RFCs 2003 through 2006 and RFC 3220 (which obsoletes RFC 2002) Local Area Mobility Cisco proprietary feature that is similar to Mobile IP Operates by using the routing table Routing in the IP Environment 39

40 Routing To and From the Internet BGPv4 The exterior routing protocol in use on the Internet Should only be used by networks that connect to multiple Internet providers Tracks hops between pairs of autonomous systems instead of tracking hop counts for actual routers Routing in the IP Environment 40

41 Securing Routers and Routing Securing routers Behavior Turn off unnecessary services Shut down unnecessary listening ports Configure strong access security to prevent tampering Secure physical access to the boxes Securing routing protocols Requires cooperation from the protocols themselves Routing in the IP Environment 41

42 Troubleshooting IP Routing ROUTE View the host s local routing table, and add and remove route entries PING Sends ICMP Echo messages and test connectivity TRACERT Sends ICMP echoes with incrementally increasing TTL values to identify the path to a destination PATHPING Utility used to discover path from host to destination Routing in the IP Environment 42

43 Summary Routing protocols and routers Provide a mechanism that can forward traffic from a sender s subnet to an intended receiver s subnet Routers Depend on various routing protocols to manage the packet forwarding process Distance vector routing protocols such as RIP Provides a crude metric of routing cost Routing in the IP Environment 43

44 Summary (continued) The OSPF protocol Supports much more sophisticated routing structures that break up a network into routing areas Routing characteristics Help to determine what kinds of routing protocols to use in specific applications Managing routing on a complex network means Understanding how and when to use exterior and interior routing protocols Routing in the IP Environment 44

45 Summary (continued) Router tables define the topology and behavior of IP networks Essential to manage router security and updates as safely as possible Troubleshooting tools for inspecting and diagnosing routing problems through Windows 2000, Windows Server 2003, and Windows XP IP host include route, tracert, ping, and pathping Routing in the IP Environment 45