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CCNA3 – module 3 EIGRP

CCNA3 – module 3 EIGRP. EIGRP. Cisco proprietary, released in 1994 Based on IGRP EIGRP is an advanced distance-vector routing protocol that relies on features commonly associated with link-state protocols. (sometimes called a hybrid routing protocol ) Supports VLSM and CIDR

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CCNA3 – module 3 EIGRP

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  1. CCNA3 – module 3 EIGRP

  2. EIGRP • Cisco proprietary, released in 1994 • Based on IGRP • EIGRP is an advanced distance-vector routing protocol that relies on features commonly associated with link-state protocols. (sometimes called a hybrid routing protocol) • Supports VLSM and CIDR • Allows for multiple routed protocols

  3. EIGRP • Uses Hello protocols to create and maintain neighbor relationships and to determine when a link is down. (Like link-state) • Every 5 seconds, with a hold timer of 15 seconds • Links less than T1 speed, Hellos are every 60 seconds, hold timer of 180 seconds • Partial routing updates in response to topology changes • When a change in topology occurs, EIGRP does not flood updates like link-state protocols, but immediately sends those changes to its neighbors. • Has speed and efficiency of routing updates like a link-state protocol, along with a topology database.

  4. EIGRP Benefits • Rapid Convergence – DUAL routing algorithm • Efficient use of bandwidth • partial, bounded updates – only sent to routers that need the information & not entire routing table • small “Hello” packets to keep in touch with other routers – minimal use of bandwidth • Supports VLSM and CIDR • Multiple network-layer support (multiprotocol) • IP, IPX, and AppleTalk

  5. EIGRP and IGRP • Automatically redistributes when using same AS number. • Topology example….

  6. Metric calculation: IGRP/EIGRP metric = [K1 * bandwidth + ((K2 * bandwidth) / (256 * load)) + (K3 * delay)] * [K5/(reliability + K4)] (with the following default constant values): Constant Value K1 1 K2 0 K3 1 K4 0 K5 0 Notes • k2 metric effects LOAD • k4 and k5 effects RELIABILITY

  7. Metric Calculation Simplify the previous equation by applying the default constants…

  8. Metric Calculation The metrics used by EIGRP in making routing decisions are (lower the metric the better): • bandwidth • delay • load • reliability By default, EIGRP uses only: • Bandwidth (carrying capacity) • Delay (end-to-end travel time)

  9. Metric Calculation If these are the default: • bandwidth (default) • delay (default) When are these used? • load • reliability Use show interface command to view the metrics used on a specific interface that is routing EIGRP.

  10. Metric Calculation – show interfaces Router> show interfaces s1/0 Serial1/0 is up, line protocol is up Hardware is QUICC Serial Description: Out to VERIO Internet address is 207.21.113.186/30 MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec, rely 255/255, load 246/255 Encapsulation PPP, loopback not set Keepalive set (10 sec) <output omitted>

  11. Metric Calculation – Bandwidth Bandwidth • Expressed in kilobits (show interface) • This is a static number and used for metric calculations only. • Does not necessarily reflect the actual bandwidth of the link. • You can adjust the bandwidth metric on an interface using what command? • What command restores the interface bandwidth to the original default? The default values: • What is the default bandwidth of serial interfaces on CISCO routers?

  12. Metric Calculation – Delay Delay • Like bandwidth, delay it is a static number. • Expressed in microseconds, millionths of a second • (Uses the Greek letter mu with an S, S, NOT “ms” which is millisecond or thousandths of a second) The default values: • What is the default delay of a Cisco serial interface? • IGRP/EIGRP metric uses the sum of all of the delays of all of the outbound interfaces to the destination network.

  13. Metric Calculation – Delay Changing the delay informational parameter: The delay can be changed using: Router(config-if)# delay tens-of-S (microseconds) Example of changing the delay on a serial interface to 30,000 microseconds: Router(config-if)# delay 3000 To restore the 20,000 microsecond default value: Router(config-if)# no delay

  14. IGRP vs EIGRP Metric Calculation The difference: • IGRP metric is 24 bits long • EIGRP metric is 32 bits long • EIGRP metric is 256 times greater for the same route • EIGRP allows for finer comparison of potential routes

  15. IGRP vs EIGRP Metric Calculation IGRP • bandwidth = (10,000,000 ÷ bandwidth) • delay = delay ÷ 10 EIGRP • bandwidth = (10,000,000 ÷ bandwidth) * 256 • delay = (delay ÷ 10) * 256 Note: The reference-bandwidth For both IGRP and EIGRP: 107, (10,000,000/bandwidth), whereas with OSPF it was 108 (100,000,000/bandwidth)

  16. Metrics – HOP COUNT • EIGRP also imposes a maximum hop count of 224 • IGRP maximum hop count of 255 • RIP maximum hop count of 15

  17. EIGRP Configuration RTA(config)# router eigrp AS RTA(config-router)# network network RTA(config-router)# eigrplog-neighbor-changes RTA(config-if)#bandwidth kilobits Enables logging of neighbor adjacency changes to monitor stability & help detect problems CISCO recommends this command. AS must be the same on all routers in the AS If AS’s are identical on a router running both IGRP and EIGRP, routing tables are redistributed automatically. EIGRP assumes default if not set. If the link is slower, router might not converge, routing updates may be lost, or suboptimal path selection may result.

  18. EIGRP tables • Neighbor • Topology • Routing

  19. EIGRP Neighbor tables • Lists adjacent routers • One table for each routed protocol that EIGRP supports RTX#show ip eigrp neighbors IP-EIGRP neighbors for process 1 H Address Interface Hold Uptime SRTT RTO Q Seq (sec) (ms) Cnt Num 1 10.2.0.2 Se1 12 00:27:39 333 1998 0 10 0 10.1.0.1 Se0 14 01:17:14 40 240 0 27

  20. EIGRP Neighbor tables • Fields in neighbor table: • Neighbor address (Address) • Hold time (Hold Uptime) • Smooth round-trip timer (SRTT) • Queue count (Q Cnt) • Sequence number (Seq No)

  21. DUAL – calculating best paths • When the hold time expires, DUAL is informed of the topology change and must recalculate the new topology. • DUAL (Diffusing Update Algorithm) – allows routers involved in a topology change to synchronize at the same time, while not involving routers that are unaffected by the change (distance-vector algorithm)

  22. EIGRP Topology tables • Contains all of the EIGRP routing tables in the autonomous system • DUAL combines information supplied by neighbor and topology tables and calculates the lowest cost routes to each destination. • EIGRP routers track changes and switch to alternate routes when necessary • DUAL places this primary route, or successor route, information in the routing table

  23. EIGRP Topology tables Topology tables includes: • Feasible distance (FD) – lowest calculated metric to each destination. • Route source (via xxx.xxx.xxx.xxx) – ID of router that originally advertised route • Reported distance (RD) – distance that an adjacent neighbor reports to specific destination • Interface information – interface through which the destination is reachable • Route status – • passive (P) – route is stable and ready for use • Active (A) – route is in the process of being recomputed by DUAL

  24. EIGRP Topology tables RTX#show ip eigrp topology IP-EIGRP Topology Table for process 100 Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply, r - Reply status P 200.10.3.0/24, 1 successors, FD is 2169856 via Connected, Serial1 via Redistributed (2169856/0) P 200.10.4.0/24, 1 successors, FD is 2169856 via Connected, Serial0 RD

  25. EIGRP Topology tables Successor – route that is selected as the primary route to use to reach a destination. • DUAL identifies and places route in routing table • There can be up to four successor routes for any particular route. • Copy of successor is also placed in topology table EIGRP sorts the topology table so that the successor routes are at the top, followed by the feasible successors. Bottom of list may include routes that DUAL believes to be loops.

  26. EIGRP Topology tables Feasible Successor – backup route • Identified at same time as successor but kept only in the topology table • May have multiple feasible successors but not mandatory to have any • They are neighbors that are downstream (closer to the destination) • Must have lower advertised cost (RD) than existing successor’s FD • If feasible successor not identified, active status placed on route and query packets sent to all neighbors to recompute topology.

  27. Successor & Feasible Successor

  28. Recomputation of Routes • If route becomes unavailable and DUAL cannot find feasible successor. • Neighbor routers are compelled to answer query for a loop-free path. • If neighbor has no route, it responds so. • Excess computation = network instability • To prevent convergence problems, DUAL always tries to find a feasible successor before resorting to recomputation

  29. Recomputation of Routes • Stuck in Active routers – • one or more routers don’t respond to query (180 seconds) then routes placed in stuck in active state • EIGRP then clears its table of neighbors that did not respond

  30. Route Tagging • Routing Table – • Internal routes • routes originating within the EIGRP AS • External routes • routes originating outside the EIGRP AS

  31. Routing Table & Tagging RouterB#show ip route Codes: 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 not set C 10.1.1.0 is directly connected, Serial0 D172.16.0.0 [90/2681856] via 10.1.1.0, Serial0 D EX 192.168.1.0 [170/2681856] via 10.1.1.1, 00:00:04, Serial0 • External EIGRP routes are redistributed from IGRP networks

  32. External EIGRP routes are redistributed from IGRP networks 192.168.1.0 was redistributed from IGRP RTA#show ip route <output omitted> C 10.1.1.0 is directly connected, Serial0 D172.16.0.0 [90/2681856] via 10.1.1.0, Serial0 D EX 192.168.1.0 [170/2681856] via 10.1.1.1, 00:00:04, Serial0 RTC#show ip route <output omitted> C 192.168.1.0 is directly connected, Serial0 I 10.1.0.0 [100/10476] via 192.168.1.1, 00:00:04, Serial0 I 172.16.0.0 [100/10476] via 192.168.1.1, 00:00:04, Serial0 RTC only sees IGRP routes

  33. Hellos & RTP • Hello Packets • Sent every 5 seconds (high-bandwidth links) and every 60 seconds by default (low-bandwidth links) • As long as routers receive hello packets – route in passive state • Reliable Transport Protocol (RTP) • Layer 4 protocol • Guarantees delivery of packets • Allows EIGRP to multicast and unicast to different peers simultaneously

  34. DUAL FSM • DUAL Finite-State Machine (DUAL FSM) • Full name of DUAL technology • Tracks routes advertised by neighbors and uses composite metric to compare them • Guarantees each path is loop-free • Inserts lowest-cost paths (successor routes) into routing table • Neighbor & Topology tables supply DUAL with route information to make decisions quickly

  35. DUAL FSM 2 < 3 FD is not mandatory

  36. EIGRP Packets • Hello Packets • 5 second updates (T1/Point-to-Point link) • Multicast on IP address 224.0.0.10 • Hold Time = 3 times the Hello interval • (15 seconds) • Neighbor routers hello and dead intervals do not need to match with EIGRP (unlike OSPF)

  37. EIGRP Packets • Acknowledgement • Used by RTP to signal reliable exchange of information • Hello packet without data; unicast to specific host • Update • Discovery of new neighbor • EIGRP router sends unicast to neighbor so that it can add to its topology table • EIGRP router send multicast to all neighbors if topology change occurs

  38. EIGRP Packets • Query & Reply • Query - Used to obtain specific information from one or all of its neighbors (multicast or unicast) • Reply – response to query (unicast) • Used, for example, if DUAL places a route in active state and multicasts neighbors, searching for successor

  39. EIGRP Route Summarization EIGRP automatically summarizes routes at the classful boundary This may not be preferable, especially if using VLSM To disable auto-summarization: Router(config-router)#no auto-summary Manual Summarization command: Router(config-if)#ip summary-address eigrp AS ip-address subnet-mask administrative distance (configured on a per-interface basis)

  40. EIGRP Route Summarization

  41. Verifying EIGRP • Show ip eigrp neighbors • Show ip eigrp interfaces • Show ip eigrp topology • Show ip eigrp topology all-links • Show ip eigrp traffic AS • Debug eigrp fsm • Debug eigrp packets

  42. RIP, IGRP, & OSPF Troubleshooting • Show & debug commands • Debug ip rip • Debug ip igrp events • Debug ip igrp transactions • Debug ip ospf events • Show ip route • Show running-config • Show ip protocols • show ip ospf neighbor

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