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Year 2 - Chapter 5/Cisco 3 - Module 5 Routing Protocols: IGRP. By Carl Marandola. Objectives. Describe the routing functions of the network layer and how these functions relate to path determination in a router Describe routed and routing protocols Describe interior and exterior protocols - PowerPoint PPT Presentation
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Copyright 2002
Year 2 - Chapter 5/Cisco 3 - Module 5
Routing Protocols: IGRP
By
Carl Marandola
Copyright 2002
Objectives
• Describe the routing functions of the network layer and how these functions relate to path determination in a router
• Describe routed and routing protocols• Describe interior and exterior protocols• Describe routing protocol characteristics and
configuration• Describe IGRP features, operation, and
configuration tasks
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Network Layer Basics
• Network Layer Path Determination• Routing Tables• The Network Layer Communication Path• Addressing: The Network and the Host
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The Goals of Routing Protocols
• The Optimal (Best) Route • Simplicity and Efficiency• Robustness• Rapid Convergence• Flexibility
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Routing Table
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Path Determination
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Network and Host Addressing
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Path Selection and Packet Switching
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Static Versus Dynamic Routes
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Routing Metrics
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Complex Metrics
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Addresses and Packet Forwarding
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Routed Versus Routing Protocol
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Multiprotocol Routing
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Exterior Versus Interior Protocols
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Three Classes of Routing Protocols
• Distance Vector• Link State• Hybrid
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Issues in Choosing a Routing Protocol
• Network size and complexity • Network traffic levels • Security needs • Reliability needs • Network delay characteristics • Organizational policies • Organizational acceptance of change
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Distance-Vector Routing Basics
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Distance-Vector Topology Changes
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Understanding IGRP Operation
• Interior, System, and Exterior IGRP Routes• Creating the IGRP Routing Process• Enhancing IGRP Stability• IGRP Metric Information• IGRP Updates• Maximum Hop Count
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IGRP Overview
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IGRP Key Information• Cisco proprietary protocol
– Requires all Cisco devices.
• Distance-vector routing protocol• Periodic updates every 90 seconds
– Full route table exchanged.– Declares a route inaccessible after three missed update
periods (270 seconds).– Route removed after seven update periods (630 seconds).
• Metric based on bandwidth and delay by default– Optional: Can include reliability, load, and MTU.
• Large network diameter – 100 hops (routers)– Optional: Up to 255 possible.
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Interior and Exterior Routes
InternetISP
Exterior route
Interior routes
An AS is a collection of networks under common administration sharing a common routing strategy. Typically this would be a company, but a large company could create multiple ASs.
Typically ISPs and clients do not share routing information or protocols. Exterior routes are typically a default route to the ISP and static route(s) to the AS.
All routers running IGRP or Enhanced IGRP (EIGRP) and using the same AS number will exchange route information.
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IGRP Configuration
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Configuring IGRP ExampleRouter(config)#router igrp 100Router(config-router)#network 219.17.100.0Router(config-router)#network 199.6.13.0Router(config-router)#network 201.100.11.0
If you want the bandwidth on a serial link to be interpreted by IGRP as anything but 1.54 Mbps (T1 – default), you must use the optional bandwidth command. This command gives IGRP a value to use but does not alter the actual bandwidth. The following example sets the bandwidth to 256 Kbps:
Router(config)#int s0Router(config-if)#ip address 219.17.100.1 255.255.255.0Router(config-if)#bandwidth 256Router(config-if)#no shutdown
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The show ip route Command
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 N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2 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 U - per-user static route, o - ODR
Gateway of last resort is not set
C 204.204.7.0/24 is directly connected, Serial1I 223.8.151.0/24 [100/8576] via 204.204.7.1, 00:01:06, Serial1I 199.6.13.0/24 [100/10476] via 204.204.7.1, 00:01:06, Serial1C 210.93.105.0/24 is directly connected, Ethernet0
MetricAdministrative Distance Source InterfaceReceived On
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The show ip protocols Command
Router#show ip protocols Routing Protocol is "igrp 100" Sending updates every 90 seconds, next due in 69 seconds Invalid after 270 seconds, hold down 280, flushed after 630 Outgoing update filter list for all interfaces is not set Incoming update filter list for all interfaces is not set Default networks flagged in outgoing updates Default networks accepted from incoming updates IGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0 IGRP maximum hopcount 100 IGRP maximum metric variance 1 Redistributing: igrp 100 Routing for Networks: 219.17.100.0 199.6.13.0 201.100.11.0 Routing Information Sources: Gateway Distance Last Update Distance: (default is 100)
Administrative Distance
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The debug igrp events Command
Router#debug ip igrp eventsIGRP event debugging is onRouter#IGRP: sending update to 255.255.255.255 via Ethernet0 (210.93.105.1)IGRP: Update contains 0 interior, 3 system, and 0 exterior routes.IGRP: Total routes in update: 3IGRP: sending update to 255.255.255.255 via Serial1 (204.204.7.2)IGRP: Update contains 0 interior, 1 system, and 0 exterior routes.IGRP: Total routes in update: 1IGRP: received update from invalid source 223.8.151.1 on Ethernet0IGRP: received update from 204.204.7.1 on Serial1IGRP: Update contains 0 interior, 2 system, and 0 exterior routes.IGRP: Total routes in update: 2
Router#undebug allIGRP event debugging is off
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The debug igrp transactions Command
Router#debug ip igrp transactions IGRP protocol debugging is onRouter#IGRP: received update from invalid source 223.8.151.1 on Ethernet0IGRP: received update from 204.204.7.1 on Serial1 network 223.8.151.0, metric 8576 (neighbor 1100) network 199.6.13.0, metric 10476 (neighbor 8476)IGRP: sending update to 255.255.255.255 via Ethernet0 (210.93.105.1) network 204.204.7.0, metric=8476 network 223.8.151.0, metric=8576 network 199.6.13.0, metric=10476IGRP: sending update to 255.255.255.255 via Serial1 (204.204.7.2) network 210.93.105.0, metric=1100
Router#undebug allIGRP event debugging is off
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IGRP Solutions for Routing LoopsIGRP features to enhance stability include :
– Hold-down timers• If Router 1 tells Router 2 that Network A is
unavailable and Router 2 sets a hold-down timer, it will not accept information about Network A from other routers until the timer expires.
– Split horizon • Router 2 will not send routes to Router 1 that
it learned about from Router 1 (such as Network A).
– Poison reverse updates• Typically used with hold-down timers.
• If Network A goes down and Router 1 drops it from its routing updates, it will take 3 cycles (270 seconds) for Router 2 to suspect a problem and 7 cycles (630 seconds) to drop the route.
• Alternative: Router 1 sends Router 2 an update on Network A with the hop count set to 101 – infinity (unreachable) .
