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Switching Basics and Intermediate Routing CCNA 3 Chapter 3 www.ciscopress.com EIGRP and Troubleshooting Routing Protocols - Introduction • EIGRP (Enhanced IGRP) is a proprietary Cisco routing protocol based on IGRP – Supports VLSM and CIDR – Compared to IGRP: • Faster convergence times • Improved scalability • Superior management of routing loops • EIGRP is a hybrid routing protocol – Offers the best of distance vector and link-state protocols www.ciscopress.com EIGRP and Troubleshooting Routing Protocols – Introduction • Features of EIGRP: – Partial updates – Neighbor discovery – Easier to configure than OSPF – Ideal choice for large, multiprotocol networks built primarily with Cisco routers www.ciscopress.com EIGRP and Troubleshooting Routing Protocols – Introduction • Reasons network problems occur: – Commands are entered incorrectly – Access lists are constructed or placed incorrectly – Routers, switches, or other network devices are configured incorrectly – Physical connections are bad www.ciscopress.com EIGRP Concepts • Balanced hybrid routing protocols like EIGRP combine aspects of distance vector and linkstate protocols – Uses distance vectors with more accurate metrics to determine best paths to destination networks – Uses topology changes to trigger updates instead of using periodic updates – Converges more rapidly than distance vector – Uses less bandwidth, memory and processor overhead www.ciscopress.com EIGRP Concepts Comparing EIGRP and IGRP • EIGRP uses metric calculations similar to IGRP – Supports unequal-cost load balancing • EIGRP has better: – Convergence properties – Operating efficiency – Network overhead • The metric is the same (bandwidth and delay by default), but EIGRP has a weight assigned to the metric that is 256 times that for IGRP – Automatic redistribution between IGRP and EIGRP in same AS www.ciscopress.com EIGRP Concepts Comparing EIGRP and IGRP • EIGRP has a maximum hop count of 224 • EIGRP uses convergence technology called Diffusing Update Algorithm (DUAL) – Guarantees loop-free operation at every instant throughout a route computation – Allows all devices involved in a topology change to synchronize simultaneously – Routers not affected by topology changes are not involved in recomputations – The convergence time of DUAL rivals that of any other existing routing protocol www.ciscopress.com EIGRP Concepts EIGRP Features • EIGRP has rapid convergence times – Almost instantaneous • Uses DUAL to achieve rapid convergence • Stores backup routes for destinations in routing table • If no backup route available, queries neighbors • Queries are propagated until an alternate route is found www.ciscopress.com EIGRP Concepts EIGRP Features • EIGRP has low usage of network resources during normal operation – Only hello packets are sent on a stable network • Uses EIGRP hello packets to establish relationships with neighboring EIGRP routers • Builds a neighbor table from the hello packets it receives from adjacent EIGRP routers – Does not send period routing updates www.ciscopress.com EIGRP Concepts EIGRP Features • EIGRP supports automatic (classful) route summarization at major network boundaries by default • Manual route summarization can be configured on arbitrary network boundaries to reduce the size of the routing table www.ciscopress.com EIGRP Concepts EIGRP Terminology www.ciscopress.com EIGRP Concepts EIGRP Terminology Routing Protocols Supported by EIGRP www.ciscopress.com EIGRP Concepts EIGRP Terminology Contents of Tables Used by EIGRP www.ciscopress.com EIGRP Concepts EIGRP Terminology • Reliable Transport Protocol (RTP) is a transport layer protocol that guarantees ordered delivery of EIGRP packets to all neighbors – Does not rely on TCP/IP to exchange routing information, as EIGRP is protocol-independent – RTP is a proprietary protocol • EIGRP can call on RTP to provide reliable or unreliable service as needed – Can simultaneously multicast and unicast to different peers, which allows for maximum efficiency www.ciscopress.com EIGRP Concepts EIGRP Packet Types • EIGRP uses hello packets – They discover, verify and rediscover neighbor routers • Hello packets are always sent unreliably – No acknowledgement is transmitted – Hello packets are sent at a fixed interval, depending on the interface’s bandwidth – Hello packets are sent to the multicast IP address 224.0.0.10 – On low-speed networks (T1 or slower), hello packets are sent every 60 seconds; on faster networks they are sent every 5 seconds www.ciscopress.com EIGRP Concepts EIGRP Packet Types • Packets must be received within the hold time interval period to maintain a passive state, which is a reachable and operational status – If EIGRP does not receive a packet from a neighbor within the hold time, it considers that neighbor down – DUAL then reevaluates the routing table – By default, the hold time is three times the hello interval www.ciscopress.com EIGRP Concepts EIGRP Packet Types • EIGRP does not require that neighbors have the same hello intervals and dead intervals (OSPF does) – Neighbors learn about the times through the exchange of hello packets – They use the information to make stable relationships regardless of timer settings www.ciscopress.com EIGRP Concepts EIGRP Packet Types • EIGRP routers use acknowledgement packets to indicate receipt of EIGRP packets during a reliable exchange – RTP provides reliable communication – Acknowledgement packets are hello packets without data – Acknowledgement packets are unicast, hello packets are multicast – Acknowledgements can be attached to other kinds of EIGRP packets, such as reply packets www.ciscopress.com EIGRP Concepts EIGRP Packet Types • EIGRP uses update packets when a router discovers a new neighbor – Unicast packets are sent to the new neighbor so it can add to its topology table – More than one update packet may be needed • Update packets are also used when a router detects a topology change – The router sends a reliable multicast to all neighbors www.ciscopress.com EIGRP Concepts EIGRP Packet Types • EIGRP routers use query packets when they need specific information from one or all neighbors • If a router loses its successor route and cannot find a feasible successor: – DUAL places the route in active state – A query is multicast to all neighbors in an attempt to locate a successor – Neighbors send replies indicating whether or not they have a successor www.ciscopress.com EIGRP Configuration Basic EIGRP Configuration • The router eigrp and network commands create an EIGRP routing process: – Router(config)#router eigrp AS-number – Router(config)#network network-number Simple EIGRP Network www.ciscopress.com EIGRP Configuration Basic EIGRP Configuration www.ciscopress.com EIGRP Configuration Basic EIGRP Configuration Router A Command Descriptions from Previous Slide www.ciscopress.com EIGRP Configuration Basic EIGRP Configuration • When using serial links with EIGRP, the bandwidth setting must be configured on the interface – Otherwise EIGRP assumes the default bandwidth and not the true bandwidth • If the link is slower, the routers might not converge – To set the bandwidth use this syntax: • Router(config-if)#bandwidth kbps • Cisco also recommends adding the following command to all EIGRP configurations: – Router(conf-router)#eigrp log-neighbor-changes • Monitors stability of routing system www.ciscopress.com EIGRP Configuration Configuring EIGRP Summarization Effect of Autosummarization is to Summarize at the Classful Boundary www.ciscopress.com EIGRP Configuration Configuring EIGRP Summarization • In many instances, autosummarization is not the preferred option – Case of discontiguous subnets • Autosummarization prevents routers from learning about discontiguous networks • With autosummarization turned off, EIGRP routers will advertise subnets • Use this command syntax to turn off autosummarization: – Router(config-router)#no auto-summary www.ciscopress.com EIGRP Configuration Configuring EIGRP Summarization • With EIGRP, a summary address can be manually configured on a per-interface basis (use the following syntax, all on one command line): – Router(config-if)#ip summary-address eigrp autonomous-system-number ip-address mask administrative-distance www.ciscopress.com EIGRP Configuration Configuring EIGRP Summarization Discontiguous Subnets With and Without Autosummarization www.ciscopress.com EIGRP Configuration Configuring EIGRP Summarization • By default, EIGRP summary routes have an administrative distance of 5; can be configured for any distance from 1 to 255 Granular Routing Updates with Interface Summarization www.ciscopress.com EIGRP Configuration Configuring EIGRP Summarization Using Interface Summarization with EIGRP • Autosummarization is turned off with the no auto-summary command www.ciscopress.com EIGRP Configuration Verifying the EIGRP Configuration Numerous show Commands Verify EIGRP Configuration www.ciscopress.com Troubleshooting Routing Protocols • A foundation for building a problem-solving process: – When analyzing a network failure, make a clear problem statement – Gather the facts needed to help isolate possible causes – Consider possible problems based on gathered facts – Create an action plan based on potential problems – Implement the action plan – Analyze the results to determine if the problem has been solved – If not, create an action plan based on the next most likely problem on the list – After the actual cause of the problem is identified, solve it www.ciscopress.com Troubleshooting Routing Protocols • Cisco routers provide integrated commands to help in troubleshooting: – The show commands help monitor installation behavior, normal network behavior, and isolate problem areas – The debug commands assist in the isolation of protocol and configuration problems – TCP/IP tools such as ping, traceroute and Telnet help isolate the OSI layer where the problem exists www.ciscopress.com Troubleshooting Routing Protocols Troubleshooting RIP • The most common problem in RIP that prevents RIP routes from being advertised is VLSM – RIPv1 does not support VLSM – If RIP routes are not being advertised, check these: • • • • • • Layer 1 or Layer 2 connectivity issues VLSM subnetting is configured (can’t be used with RIPv1) Mismatched RIPv1 and RIPv2 routing configurations exist Network statements are missing or incorrectly assigned Outgoing interface is down Advertised network interface is down www.ciscopress.com Troubleshooting Routing Protocols Troubleshooting RIP • Use these commands to help with RIP troubleshooting: – The debug ip rip command displays information on RIP routing transactions – Use the no debug ip rip, undebug all, or u all commands to turn off debugging Sample RIP Network for Troubleshooting www.ciscopress.com Troubleshooting Routing Protocols Troubleshooting RIP Troubleshooting with debug ip rip Might see entries such as: RIP: broadcasting general request on Ethernet0 RIP: broadcasting general request on Ethernet0 www.ciscopress.com Troubleshooting Routing Protocols Troubleshooting EIGRP • Reasons why EIGRP might not work properly: – – – – – – Layer 1 or Layer 2 connectivity issues AS numbers on EIGRP routers are mismatched Link might be congested or down Outgoing interface is down Advertised network interface is down Autosummarization is enabled on routers with discontiguous subnets • Use the no auto-summary command to disable automatic network summarization • One of the most common reasons for a missing EIGRP neighbor is a failure on the actual link www.ciscopress.com Troubleshooting Routing Protocols Troubleshooting EIGRP Using debug ip eigrp to Troubleshoot www.ciscopress.com Troubleshooting Routing Protocols Troubleshooting EIGRP The debug ip eigrp Output Fields www.ciscopress.com Troubleshooting Routing Protocols Troubleshooting EIGRP • The debug ip eigrp command generates a lot of output, use it only when network traffic is light • The debug eigrp fsm command is also used for EIGRP debugging – Displays information on DUAL feasible successor maps – Helps engineers analyze packets that are sent and received on an interface www.ciscopress.com Troubleshooting Routing Protocols Troubleshooting OSPF • The majority of problems with OSPF relate to formation of adjacencies and synchronization of link-state databases Output from the debug ip ospf events Command www.ciscopress.com Troubleshooting Routing Protocols Troubleshooting OSPF • The debug ip ospf events output seen in the previous slide might appear if: – The subnet masks for routers on the same network do not match – The OSPF hello interval for the router does not match that configured for a neighbor – The OSPF dead interval does not match that configured for a neighbor • If a router configured for OSPF routing does not see an OSPF neighbor on an attached network, perform these tasks: – Make sure both routers have been configured with the same IP mask, OSPF hello interval, and OSPF dead interval – Make sure that both neighbors are part of the same area type www.ciscopress.com Troubleshooting Routing Protocols Troubleshooting OSPF To Provide Detailed Output Relating to OSPF, Use the debug ip ospf packet command www.ciscopress.com Troubleshooting Routing Protocols Troubleshooting OSPF Output Fields for the debug ip ospf packet Command www.ciscopress.com Summary • EIGRP characteristics – Interior Gateway Protocol – Quick convergence times with minimum traffic – Enhanced version of IGRP; Cisco proprietary protocol • EIGRP and IGRP are compatible, with some differences – EIGRP offers multiprotocol support – EIGRP uses same metric as IGRP – EIGRP uses a multiplier of 256 which makes the EIGRP metrics larger that IGRP metrics www.ciscopress.com Summary • EIGRP routers keep route and topology information in RAM – Information is saved in three tables • Neighbor table lists adjacent routers • Topology table has all the routes in the AS • The routing table holds the best routes to a destination • DUAL takes the information in the neighbor and topology tables and calculates the lowest cost to each destination – This is called the successor route – The backup route is called the feasible successor www.ciscopress.com Summary • EIGRP is a balanced hybrid routing protocol – Acts as a link-state protocol when updating neighbors and maintaining routing information – Advantages include: • • • • • Rapid convergence Efficient use of bandwidth Support for VLSM and CIDR Support for multiple network layers Independence from routed protocols www.ciscopress.com Summary • DUAL results in the fast convergence of EIGRP – Each router constructs a topology table • The topology table identifies the routing protocol (EIGRP), the lowest cost of the route (the feasible distance) • The cost of the route as reported by the neighbor (the reported distance) • EIGRP commands vary depending on which routed protocol is used – The network command configures connected networks • EIGRP automatically summarizes routes at classful boundaries prior to IOS Release 12.2(8)T – If discontiguous subnets exist, autosummarization must be turned off www.ciscopress.com Summary • Manual summarization is done at the interface level with the ip summary-address eigrp • The show ip eigrp command can verify the EIGRP configuration • The debug ip eigrp command can display information on eigrp packets and troubleshoot EIGRP • Troubleshooting can be approached with an eight-step troubleshooting methodology • Network engineers rely on show and debug commands to troubleshoot routing protocols • RIP, IGRP, EIGRP, and OSPF have their own set of debug commands tailored for troubleshooting www.ciscopress.com