© 2002, Cisco Systems, Inc. All rights reserved. 1 Determining IP Routes

© 2002, Cisco Systems, Inc. All rights reserved. ICND v2.0—5-2 Routed Versus Routing Protocol A routed protocol: –Includes any network protocol suite that provides enough information in its network layer address to allow a router to forward it to the next device and ultimately to its destination. –Defines the format and use of the fields within a packet. A routing protocol: –Provides processes for sharing route information. –Allows routers to communicate with other routers to update and maintain the routing tables.

© 2002, Cisco Systems, Inc. All rights reserved. ICND v2.0—5-3 IP as a Routed Protocol IP is a connectionless, unreliable, best-effort delivery protocol. As information flows down the layers of the OSI model; the data is processed at each layer. IP accepts whatever data is passed down to it from the upper layers.

© 2002, Cisco Systems, Inc. All rights reserved. ICND v2.0—5-4 Packet Propagation and Switching Within a Router

© 2002, Cisco Systems, Inc. All rights reserved. ICND v2.0—5-5 Packet Propagation and Switching Within a Router As a frame is received at a router interface. The MAC address is checked to see if the frame is directly addressed to the router interface, or a broadcast. The frame header and trailer are removed and the packet is passed up to Layer 3. The destination IP address is compared to the routing table to find a match. The packet is switched to the outgoing interface and given the proper frame header. The frame is then transmitted.

© 2002, Cisco Systems, Inc. All rights reserved. ICND v2.0—5-6 To route, a router needs to do the following: Know the destination address Identify the sources it can learn from Discover possible routes Select the best route Maintain and verify routing information What Is Routing?

© 2002, Cisco Systems, Inc. All rights reserved. ICND v2.0—5-7 Routers must learn destinations that are not directly connected. What Is Routing? (Cont.)

© 2002, Cisco Systems, Inc. All rights reserved. ICND v2.0—5-8 Static Route Uses a route that a network administrator enters into the router manually Dynamic Route Uses a route that a network routing protocol adjusts automatically for topology or traffic changes Identifying Static and Dynamic Routes

© 2002, Cisco Systems, Inc. All rights reserved. ICND v2.0—5-9 Static Routes Configure unidirectional static routes to and from a stub network to allow communications to occur.

© 2002, Cisco Systems, Inc. All rights reserved. ICND v2.0—5-10 Static Route Example This is a unidirectional route. You must have a route configured in the opposite direction.

© 2002, Cisco Systems, Inc. All rights reserved. ICND v2.0—5-11 Default Routes This route allows the stub network to reach all known networks beyond router A.

© 2002, Cisco Systems, Inc. All rights reserved. ICND v2.0—5-12 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 to network /8 is subnetted, 1 subnets C is directly connected, Serial0 S* /0 is directly connected, Serial0

© 2002, Cisco Systems, Inc. All rights reserved. ICND v2.0—5-13 Routing protocols are used between routers to determine paths and maintain routing tables. Once the path is determined, a router can route a routed protocol. What Is a Routing Protocol?

© 2002, Cisco Systems, Inc. All rights reserved. ICND v2.0—5-14 Routers discover the best path to destinations from each neighbor. Sources of Information and Discovering Routes

© 2002, Cisco Systems, Inc. All rights reserved. ICND v2.0—5-15 Classes of Routing Protocols

© 2002, Cisco Systems, Inc. All rights reserved. ICND v2.0—5-16 Distance Vector RIPv1 RIPv2 Link State OSPF IS-IS Hybrid Routing EIGRP Classes of Routing Protocols

© 2002, Cisco Systems, Inc. All rights reserved. ICND v2.0—5-17 Distance Vector Routing Protocol s

© 2002, Cisco Systems, Inc. All rights reserved. ICND v2.0—5-18 Routers pass periodic copies of routing table to neighbor routers and accumulate distance vectors. Distance Vector Routing Protocols

© 2002, Cisco Systems, Inc. All rights reserved. ICND v2.0—5-19 Maximum is 6 paths (default = 4) Hop-count metric selects the path Routes update every 30 seconds RIP ( Distance Vector Routing Protocol )

© 2002, Cisco Systems, Inc. All rights reserved. ICND v2.0—5-20 Starts the RIP routing process Router(config)#router rip Router(config-router)#network network-number Selects participating attached networks Requires a major classful network number RIP Configuration

© 2002, Cisco Systems, Inc. All rights reserved. ICND v2.0—5-21 RIP Configuration Example

© 2002, Cisco Systems, Inc. All rights reserved. ICND v2.0—5-22 Displaying the IP Routing Table

© 2002, Cisco Systems, Inc. All rights reserved. ICND v2.0—5-23 RIPv2 Distance vector protocol like RIP. Same AD, update timer and metric as RIP. But supports classless ip routing. Uses multicast address

© 2002, Cisco Systems, Inc. All rights reserved. ICND v2.0—5-24 © 2002, Cisco Systems, Inc. All rights reserved. 24 Link-State Routing (OSPF)

© 2002, Cisco Systems, Inc. All rights reserved. ICND v2.0—5-25 After initial flood, pass small event-triggered link-state updates to all other routers Link-State Routing Protocols

© 2002, Cisco Systems, Inc. All rights reserved. ICND v2.0—5-26 Benefits of Link-State Routing Fast convergence: changes are reported immediately by the source affected.

© 2002, Cisco Systems, Inc. All rights reserved. ICND v2.0—5-27 OSPF as a Link-State Protocol OSPF propagates link-state advertisements rather than routing table updates. LSAs are flooded to all OSPF routers in the area. The OSPF link-state database is pieced together from the LSAs generated by the OSPF routers. OSPF uses the SPF algorithm to calculate the shortest path to a destination. –Link = router interface –State = description of an interface and its relationship to neighboring routers

© 2002, Cisco Systems, Inc. All rights reserved. ICND v2.0—5-28 OSPF Hierarchical Routing Consists of areas and autonomous systems Minimizes routing update traffic

© 2002, Cisco Systems, Inc. All rights reserved. ICND v2.0—5-29 Configuring Single Area OSPF Router(config-router)#network address mask area area-id Assigns networks to a specific OSPF area Router(config)#router ospf process-id Defines OSPF as the IP routing protocol

© 2002, Cisco Systems, Inc. All rights reserved. ICND v2.0—5-30 OSPF Configuration Example

© 2002, Cisco Systems, Inc. All rights reserved. ICND v2.0—5-31 Router#show ip ospf interface Verifying the OSPF Configuration Displays area-ID and adjacency information Router#show ip protocols Verifies that OSPF is configured Router#show ip route Displays all the routes learned by the router Router#show ip ospf neighbor Displays OSPF-neighbor information on a per-interface basis

© 2002, Cisco Systems, Inc. All rights reserved. ICND v2.0—5-32 Drawbacks to Link-State Routing Protocols Initial discovery may cause flooding. Memory- and processor-intensive.

© 2002, Cisco Systems, Inc. All rights reserved. ICND v2.0—5-33 © 2002, Cisco Systems, Inc. All rights reserved. 33 Balanced Hybrid Routing ( EIGRP)

© 2002, Cisco Systems, Inc. All rights reserved. ICND v2.0—5-34 Shares attributes of both distance vector and link-state routing Balanced Hybrid Routing

© 2002, Cisco Systems, Inc. All rights reserved. ICND v2.0—5-35 Introducing EIGRP EIGRP FEATURES Metric: Bandwidth, delay, load, reliability Event triggered updates Exchange updates like distance vector.

© 2002, Cisco Systems, Inc. All rights reserved. ICND v2.0—5-36 EIGRP Terminology

© 2002, Cisco Systems, Inc. All rights reserved. ICND v2.0—5-37 Configuring EIGRP Router(config-router)#network network-number Selects participating attached networks Router(config)#router eigrp autonomous-system Defines EIGRP as the IP routing protocol

© 2002, Cisco Systems, Inc. All rights reserved. ICND v2.0—5-38 EIGRP Configuration Example

© 2002, Cisco Systems, Inc. All rights reserved. ICND v2.0—5-39 Verifying the EIGRP Configuration Router#show ip protocols Router#show ip route eigrp Router#show ip eigrp traffic Router#show ip eigrp neighbors Router#show ip eigrp topology Displays the neighbors discovered by IP EIGRP Displays the IP EIGRP topology table Displays the number of IP EIGRP packets sent and received Displays current EIGRP entries in the routing table Displays the parameters and current state of the active routing protocol process