1 CCNA 3 v3.1 Module 3

2 CCNA 3 Module 3 Enhanced Interior Gateway Routing Protocol (EIGRP)

333 EIGRP Cisco-proprietary routing protocol Based on Interior Gateway Routing Protocol (IGRP) How does EIGRP improve on IGRP Supports classless interdomain routing (CIDR) Network designers can maximize address space Variable-length subnet mask (VLSM) Fast convergence times Improved scalability Superior handling of routing loops. Hybrid routing protocol combining distance vector and link-state algorithms An ideal choice for large, multi-protocol networks built primarily on Cisco routers

444 EIGRP Versus IGRP Compatibility mode IGRP and EIGRP are interoperable EIGRP offers multiprotocol support Metric calculation (Bandwidth + Delay) EIGRP - 32 bit metric for bandwidth and delay IGRP – 24 bit metric for bandwidth and delay IGRP Bandwidth = /bandwidth Kbps EIGRP Bandwidth = ( /bandwidth Kbps)*256 IGRP Delay = delay/10 EIGRP Delay = (delay / 10) * 256

555 Hop count IGRP maximum hop is 255 EIGRP maximum hop is 224 Automatic protocol redistribution IGRP and EIGRP can share routes if both have the same autonomous system number Route tagging EIGRP tags routes learned from IGRP as external IGRP does not tag routes Holddown timers EIGRP 180 IGRP 280

666 D = EIGRP routing EX = External route I = IGRP routing

777 EIGRP Terminology and Concepts Holds route and topology information in RAM EIGRP Tables Neighbor Table Topology Table Routing Table

888 Neighbor Table Lists adjacent routers Similar to OSPFs adjacency database One for each protocol EIGRP supports Neighbors send hello packets Containing holddown timer If neighbor does not send another hello packet before holddown timer expires the neighbor is unreachable or unoperational When the hold time expires Diffusing Update Algorithm (DUAL) (EIGRP distance vector algorithm) recalculate the new topology

999 NB Fields in the neighbor table Neighbor Address Layer 3 address of neighbor router Hold time Time to wait before considering link down Smooth Round Trip timer Average time to send and receive packet Queue count Amount of IEGRP packets in queue Sequence number Number of last packet received from neighbor

10 Topology Table All EIGRP routing tables in the AS DUAL takes information from neighbor table and topology table and calculates the lowest cost routes to each destination Successor Neighbor router that is the next hop in a least cost, loop- free path to a destination All learned routes to a destination are maintained in the topology table

11 Admin distance Feasible Distance (e.g., 90) - the lowest metric (cost) to each destination Route Source (via ) – router that originally advertised that route Reported Distance (e.g., ) – cost of route as advertised by the neighbor router Interface information – The interface through which the destination is reachable Route status – passive (P) the route is stable and ready for use active (A) the route is in the process of being recomputed by DUAL FD/RD

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17 EIGRP Routing Table Holds the best routes to a destination Routing table for each network protocol. A successor is a route selected as the primary route to use to reach a destination The preferred root to the destination DUAL calculates this using neighbor and topology tables It is placed in the routing table A copy if it is placed in the topology table Up to 4 successor routes for any particular route equal or unequal cost identified as the best loop-free paths to a given destination A feasible successor (FS) is a backup route only kept in the topology table not mandatory

18 EIGRP Design Features Rapid convergence DUAL guarantees loop-free operation at every instant throughout a route computation allowing all routers involved in a topology change to synchronize at the same time Efficient use of bandwidth partial, incremental updates to routers that need the information (bounded updates) Hello packets keep routers in touch with each other Support for variable-length subnet mask (VLSM) and classless interdomain routing (CIDR) Multiple network-layer support supports IP, IPX, and AppleTalk through protocol-dependent modules (PDMs). Independence from routed protocols.

19 EIGRP Technologies 1.Neighbor discovery and recovery Form adjacencies by sending Hello packet every five seconds This allows EIGRP to Dynamically learn of new routes that join their network Identify routers that become either unreachable or inoperable Rediscover routers that had previously been unreachable 2.Reliable Transport Protocol (RTP) Transport-layer protocol guarantee ordered delivery of EIGRP packets to all neighbors – used for reliability of transmission 3.DUAL finite-state machine algorithm Contains all the logic used to calculate and compare routes in an EIGRP network DUAL tracks all the routes advertised by neighbors DUAL also guarantees that each path is loop free DUAL inserts lowest cost paths into the routing table (successor routes) DUAL places a copy of successor routes in the topology table(feasability successor) 4.Protocol-dependent modules Support for routed protocols, such as IP, IPX, and AppleTalk

20 EIGRP Data Strucutre EIGRP Packet Types Hello - discover, verify, rediscover neighbor routers Sent unreliably – no acknowledgement needed EIGRP routers send hellos to the multicast IP address Default hello interval depends on the bandwidth of the interface Acknowledgment - indicate receipt of any EIGRP packet during a reliable exchange Update - unicast update packets sent to new neighbor so that it can add to its topology table Query – to find specific information about a router Reply – response to a query

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22 EIGRP Configuration router(config)#router eigrp autonomous-system- number AS-number identifies all routers within the internetwork router(config-router)#network network-number Specify all connected networks only router(config-if)#bandwidth kilobits Set the bandwidth for the serial link router(config-if)#eigrp log-neighbor-changes enables the logging of neighbor adjacency changes to monitor the stability of the routing system and to help detect problems

23 Why is it necessary to set the bandwidth n/w may be unable to converge if bandwidth setting does not match actual bandwidth A suboptimal route may be chosen as the best path to a destination if the bandwidth setting is higher than the actual bandwidth

24 Configuring EIGRP summarization EIGRP automatically summarizes routes at the classful boundary summarization keeps routing tables as compact as possible router(config-router)#no auto-summary Turns off route summarization when manually configuring To manually configure a summary address router(config-if)#ip summary-address eigrp autonomous- system-number ip-address mask administrative- distance Administrative distance for EIGRP summary routes Default is 5 Can be configured to between 1 and 255

25 It is necessary to configure the bandwidth setting on an EIGRP interface rather than leaving it at the default setting because A suboptimal route may be chosen as the best path to a destination if the bandwidth setting is higher than the actual bandwidth of the link The network may be unable to converge if the bandwidth setting does not match the actual bandwidth of the link.

26 Verifying EIGRP Show ip eigrp neighbors Displays eigrp neighbor table Show ip eigrp interfaces Displys eigrp information for each interface Show ip eigrp topology [keyword] Displays feasible successors Keywords - Active, pending, zero successor Show ip eigrp all-links Displays all routes not just feasable successors Show ip eigrp traffic Displays the number of eigrp packets sent/recieved

27 Troubleshooting RIP RIP Problems Most common problem RIP V1prevent variable-length subnet mask (VLSM) being advertised. Layer 1 or Layer 2 connectivity issues exist. Mismatched RIP v1 and RIP v2 routing configurations exist. Network statements are missing or incorrectly assigned. The outgoing interface is down. The advertised network interface is down. Troubleshooting show ip protocols displays current state of the active routing protocol process debug ip rip Display information on RIP routing transactions Turn this off using no debug ip rip, no debug all, or undebug all

28 Troubleshooting IGRP IGRP Problem checks Layer 1 or Layer 2 connectivity issues exist. Autonomous system numbers on IGRP routers are mismatched. Network statements are missing or incorrectly assigned. The outgoing interface is down. The advertised network interface is down. To debug IGRP debug ip igrp transactions [host ip address] to view IGRP transaction information debug ip igrp events [host ip address] to view routing update information To turn off debugging, use the no debug ip igrp command.

29 Troubleshooting EIGRP Possible reasons why EIGRP is not working correctly Layer 1 or Layer 2 connectivity issues exist most common reasons for a missing neighbor is failure on the actual link Autonomous system numbers on EIGRP routers are mismatched. The link may be congested or down. The outgoing interface is down. The advertised network interface is down. Auto-summarization is enabled on routers with discontiguous subnets. Use no auto-summary to disable automatic network summarization

30 Show ip route eigrp Displays current eigrp entries in routing table Show ip protocols Displays EIGRP AS number, filtering and redistribution numbers, neighbors Show ip eigrp traffic Displays packets sent and recieved Static on hello, update, query, replies, acks Eigrp log-neighbor-changes Displays a history of when and why neighbors have been reset

31 Troubleshooting OSPF Show ip ospf neighbor Displays OSPF neighbor one each interface Displays routes known to the router and how they were learned Show ip ospf interface Displays timer intervals, neighbor adjacencies Determines if OSPF is enabled on each interface Debug ip ospf events Displays Adjacencies, Flooding information, Designated router selection, Shortest path first (SPF) calculation Debug ip ospf packets Displays information about OSPF packets received No debug ip ospf packets Turns off debugging

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