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CCNA 3 v3. 1 Module 3

CCNA 3 v3. 1 Module 3. CCNA 3 Module 3. Enhanced Interior Gateway Routing Protocol (EIGRP). EIGRP. Cisco-proprietary routing protocol Based on Interior Gateway Routing Protocol (IGRP) How does EIGRP improve on IGRP Supports classless interdomain routing ( CIDR )

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CCNA 3 v3. 1 Module 3

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  1. CCNA 3 v3.1 Module 3

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

  3. 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 protocolcombining • distance vector and link-state algorithms • An ideal choice for large, multi-protocol networks built primarily on Cisco routers

  4. 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 = 1000000/bandwidth Kbps • EIGRP Bandwidth = (1000000/bandwidth Kbps)*256 • IGRP Delay = delay/10 • EIGRP Delay = (delay / 10) * 256

  5. 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

  6. D = EIGRP routing EX = External route I = IGRP routing

  7. EIGRP Terminology and Concepts • Holds route and topology information in RAM • EIGRP Tables • Neighbor Table • Topology Table • Routing Table

  8. 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

  9. 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. FD/RD Admin distance Feasible Distance (e.g., 90) - the lowest metric (cost) to each destination Route Source (via 200.10.10.10) – router that originally advertised that route Reported Distance (e.g., 2195456) – 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

  12. 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

  13. 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.

  14. EIGRP Technologies • 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 • Reliable Transport Protocol (RTP) • Transport-layer protocol guarantee ordered delivery of EIGRP packets to all neighbors – used for reliability of transmission • 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) • Protocol-dependent modules • Support for routed protocols, such as IP, IPX, and AppleTalk

  15. 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 224.0.0.10 • 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

  16. EIGRP Configuration • router(config)#router eigrpautonomous-system-number • AS-number identifies all routers within the internetwork • router(config-router)#network network-number • Specify all connected networks only • router(config-if)#bandwidthkilobits • 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

  17. 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

  18. 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 eigrpautonomous-system-number ip-address mask administrative-distance • Administrative distance for EIGRP summary routes • Default is 5 • Can be configured to between 1 and 255

  19. 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.

  20. 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

  21. 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

  22. 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.

  23. 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

  24. 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

  25. 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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