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  • 1. Determining IP Routes Introducing Routing © 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—3-1
  • 2. Outline • Overview • Routing Overview • Static and Dynamic Route Comparison • Static Route Configuration • Default Route Forwarding Configuration • Static Route Configuration Verification • Dynamic Routing Protocol Overview • Features of Dynamic Routing Protocols • The ip classless Command • InterVLAN Routing • Summary © 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—3-2
  • 3. Router Operations To route, a router needs to do the following: • Know the destination address • Identify the sources from which the router can learn • Discover possible routes to the intended destination • Select the best route • Maintain and verify routing information © 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—3-3
  • 4. Router Operations (Cont.) • Routers must learn destinations that are not directly connected. © 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—3-4
  • 5. Identifying Static and Dynamic Routes Static Route • Uses a route that a network administrator enters into the router manually © 2006 Cisco Systems, Inc. All rights reserved. Dynamic Route • Uses a route that a network routing protocol adjusts automatically for topology or traffic changes ICND v2.3—3-5
  • 6. Static Routes • Configure unidirectional static routes to and from a stub network to allow communications to occur. © 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—3-6
  • 7. Static Route Configuration Router(config)# ip route network [mask] {address | interface}[distance] [permanent] • Defines a path to an IP destination network or subnet or host © 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—3-7
  • 8. Static Route Example • This is a unidirectional route. You must have a route configured in the opposite direction. © 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—3-8
  • 9. Default Routes • This route allows the stub network to reach all known networks beyond Router A. © 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—3-9
  • 10. Verifying the Static Route Configuration Router# show ip route Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, * - candidate default U - per-user static route Gateway of last resort is 0.0.0.0 to network 0.0.0.0 C S* 10.0.0.0/8 is subnetted, 1 subnets 10.1.1.0 is directly connected, Serial0 0.0.0.0/0 is directly connected, Serial0 © 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—3-10
  • 11. What Is a Routing Protocol? • Routing protocols are used between routers to determine paths and maintain routing tables. • After the path is determined, a router can route a routed protocol. © 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—3-11
  • 12. Autonomous Systems: Interior or Exterior Routing Protocols • An autonomous system is a collection of networks under a common administrative domain. • IGPs operate within an autonomous system. • EGPs connect different autonomous systems. © 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—3-12
  • 13. Classes of Routing Protocols © 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—3-13
  • 14. Administrative Distance: Ranking Routes © 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—3-14
  • 15. Classful Routing Overview • Classful routing protocols do not include the subnet mask with the route advertisement. • Within the same network, consistency of the subnet masks is assumed. • Summary routes are exchanged between foreign networks. • These are examples of classful routing protocols: – RIP version 1 (RIPv1) – IGRP © 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—3-15
  • 16. Classless Routing Overview • Classless routing protocols include the subnet mask with the route advertisement. • Classless routing protocols support variable-length subnet mask (VLSM). • Summary routes can be manually controlled within the network. • These are examples of classless routing protocols: – RIP version 2 (RIPv2) – EIGRP – OSPF – IS-IS © 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—3-16
  • 17. Routing Protocol Comparison Chart © 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—3-17
  • 18. Using the ip classless Command © 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—3-18
  • 19. VLAN-to-VLAN Overview • Network layer devices combine multiple broadcast domains. © 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—3-19
  • 20. Dividing a Physical Interface into Subinterfaces • Physical interfaces can be divided into multiple subinterfaces. © 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—3-20
  • 21. Routing Between VLANs with ISL Trunks © 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—3-21
  • 22. Routing Between VLANs with 802.1Q Trunks © 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—3-22
  • 23. Summary • Routing is the process by which items get from one location to another. In networking, a router is the device used to route traffic. Routers can forward packets over static routes or dynamic routes, based on the router configuration. • Static routers use a route that a network administrator enters into the router manually. Dynamic routes use a router that a network routing protocol adjusts automatically for topology or traffic changes. • Unidirectional static routes must be configured to and from a stub network to allow communications to occur. • The ip route command can be used to configure default route forwarding. • The show ip route command is used to verify that static routing is properly configured. Static routes are signified in the command output by “S.” © 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—3-23
  • 24. Summary (Cont.) • Dynamic routing protocols determine how updates are conveyed, what knowledge is conveyed, when to convey knowledge, and how to locate recipients of the updates. • A routing protocol that has a lower administrative value is more trustworthy than a protocol that has a higher administrative value. • There are three classes of routing protocols: distance vector, link-state, and balanced hybrid. • The ip classless command can be used to prevent a router from dropping a packet that is destined for an unknown subnetwork of a directly attached network if a default route is configured. • For interVLAN routing to be performed, a single physical router interface must be separated into logical subinterfaces, and ISL or 802.1Q trunking must be enabled. © 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—3-24
  • 25. © 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—3-25