© 2002, cisco systems, inc. all rights reserved. 1 determining ip routes
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Determining IP Routes
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© 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.
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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.
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Packet Propagation and Switching Within a Router
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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.
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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?
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• Routers must learn destinations that are not directly connected.
What Is Routing? (Cont.)
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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
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Static Routes
• Configure unidirectional static routes to and from a stub network to allow communications to occur.
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Static Route Example
• This is a unidirectional route. You must have a route configured in the opposite direction.
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Default Routes
• This route allows the stub network to reach all known networks beyond router A.
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Verifying the Static Route Configuration
router#show ip routeCodes: 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 10.0.0.0/8 is subnetted, 1 subnetsC 10.1.1.0 is directly connected, Serial0S* 0.0.0.0/0 is directly connected, Serial0
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• 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?
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Routers discover the best path to destinations from each neighbor.
Sources of Information and Discovering Routes
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Classes of Routing Protocols
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Distance Vector• RIPv1
• RIPv2
Link State• OSPF
• IS-IS
Hybrid Routing• EIGRP
Classes of Routing Protocols
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Distance Vector Routing Protocols
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• Routers pass periodic copies of routing table to neighbor routers and accumulate distance vectors.
Distance Vector Routing Protocols
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• Maximum is 6 paths (default = 4)
• Hop-count metric selects the path
• Routes update every 30 seconds
RIP (Distance Vector Routing Protocol)
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• 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
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RIP Configuration Example
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Displaying the IP Routing Table
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RIPv2
• Distance vector protocol like RIP.
• Same AD, update timer and metric as RIP.
• But supports classless ip routing.
• Uses multicast address 224.0.0.9
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Link-State Routing(OSPF)
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• After initial flood, pass small event-triggered link-state updates to all other routers
Link-State Routing Protocols
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Benefits of Link-State Routing
• Fast convergence: changes are reported immediately by the source affected.
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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
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OSPF Hierarchical Routing
• Consists of areas and autonomous systems
• Minimizes routing update traffic
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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
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OSPF Configuration Example
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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
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Drawbacks to Link-State Routing Protocols
• Initial discovery may cause flooding.
• Memory- and processor-intensive.
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Balanced Hybrid Routing( EIGRP)
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• Shares attributes of both distance vector and link-state routing
Balanced Hybrid Routing
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Introducing EIGRP
EIGRP FEATURES• Metric: Bandwidth, delay, load, reliability
• Event triggered updates
• Exchange updates like distance vector.
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EIGRP Terminology
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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
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EIGRP Configuration Example
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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