Configuring EIGRP

1. Configuring EIGRP BSCI Module 2-1 – Introduction to EIGRP

2. Objectives • This module will cover topics which allow students to meet the following objectives: • Describe the key capabilities that distinguish EIGRP from other routing protocols • Identify the four key technologies employed by EIGRP • Describe how EIGRP operates • Describe the five components of the metric used by EIGRP • Calculate the EIGRP metric for a range of pathways between routers • Explain how IGRP routes are integrated into EIGRP routes and vice-versa

3. Purpose of this Lesson Coverage of topics new to the “EIGRP” module of BSCI. • What’s new in this module? • EIGRP metric calculations for pathway ranges between routers.

4. EIGRP Features There are several key differences with EIGRP from other routing protocols which are explored in this module.

5. EIGRP Key Technologies • Neighbor discover/recovery • Reliable Transport Protocol (RTP) • DUAL finite-state machine • Protocol-dependent modules (PDMs)

6. The Diffusing Update Algorithm (DUAL) • How does EIGRP determine which routes are loop-free? • Each of A’s neighbors is reporting reachability to E: • B with a cost of 10 • C with a cost of 10 • D with a cost of 30 • These three costs are called the reported distance (RD); the distance each neighbor is reporting to a given destination

7. The Diffusing Update Algorithm (DUAL) • At A, the total cost to reach E is: • 20 through B • 25 through C • 45 through D • The best of these three paths is the path through B, with a cost of 20 • This is the feasible distance (FD)

8. The Diffusing Update Algorithm (DUAL) • A uses the FD and the RD to determine which paths are loop-free • The best path (FD) is used as a benchmark; all paths with RDs lower than the FD cannot contain loops • The algorithm may mark some loop-free paths as loops • However, it is guaranteed never to mark a looped path as loop-free

9. The Diffusing Update Algorithm (DUAL) • At A: • The path through B is the best path (FD), at 20 • C can reach E with a cost of 10; 10 (RD) is less than 20 (FD), so this path is loop-free. • D can reach E with a cost of 30; 30 (RD) is not less than 20 (FD), so EIGRP assumes this path is a loop.

10. EIGRP Topology Table

11. Seconds Remaining Before Declaring Neighbor Down How Long Since the Last Time Neighbor Was Discovered How Long It Takes for This Neighbor To Respond To Reliable Packets How Long to Wait Before Retransmitting If No Acknowledgement EIGRP Neighbor Status RTRA#showip eigrp neighbors IP-EIGRP neighbors for process 1 H Address Interface Hold Uptime SRTT RTO Q Seq (sec) (ms) Cnt Num 2 10.1.1.1 Et0 12 6d16h 20 200 0 233 1 10.1.4.3 Et1 13 2w2d 87 522 0 452 0 10.1.4.2 Et1 10 2w2d 85 510 0 3

12. EIGRP IP Routing Table

13. Example: EIGRP Tables Router C’s tables:

14. EIGRP Packets • Hello: Establish neighbor relationships. • Update: Send routing updates • Query: Ask neighbors about routing information • Reply: Respond to query about routing information • ACK: Acknowledge a reliable packet

15. Initial Route Discovery

16. EIGRP Metric • Same metric components as IGRP: • Bandwidth • Delay • Reliability • Loading • MTU • EIGRP metric is IGRP metric multiplied by 256

17. EIGRP Metric Calculation • By default, EIGRP metric: • Metric = bandwidth (slowest link) + delay (sum of delays) • Delay = sum of the delays in the path, in tens of microseconds, multiplied by 256. • Bandwidth = [10 / (minimum bandwidth link along the path, in kilobits per second)] * 256 • Formula with default K values (K1 = 1, K2 = 0, K3 = 1, K4 = 0, K5 = 0): • Metric = [K1 * BW + ((K2 * BW) / (256 – load)) + K3 * delay] • If K5 not equal to 0: • Metric = Metric * [K5 / (reliability + K4)]

18. EIGRP Metrics Calculation Example A  B  C  D Least bandwidth 64 kbps Total delay 6,000 A  X  Y  Z  D Least bandwidth 256 kbps Total delay 8,000 • Delay is the sum of all the delays of the links along the paths:Delay = [delay in tens of microseconds] x 256 • BW is the lowest bandwidth of the links along the paths:BW = [10,000,000 / (bandwidth in kbps)] x 256

19. EIGRP Metrics Are Backward-Compatible with IGRP

20. Summary • EIGRP capabilities include fast convergence and support for VLSM, partial updates, and multiple network layer protocols. • EIGRP key technologies are: neighbor discovery/recovery, RTP, DUAL finite-state machine, and protocol-dependent modules. • EIGRP uses three tables: neighbor table, topology table, and routing table. The routing table contains the best route to each destination, called the successor route. A feasible successor route is a backup route to a destination; it is kept in the topology table. • EIGRP uses the same metric components as IGRP: delay, bandwidth, reliability, load, and MTU. • By default, EIGRP metric = bandwidth (slowest link) + delay (sum of delays).  • EIGRP metrics are backward-compatible with IGRP; the EIGRP-equivalent metric is the IGRP metric multiplied by 256.

21. Self Check • What is a reported distance? • What is a feasible distance? • EIGRP uses three tables: name the three tables: __________, ____________, _____________. Which of the tables contains the best route or successor route to each destination? • EIGRP uses what metrics? __________, _________, _________, __________, ___________

22. Resources • http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a008009405c.shtml • http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080093f07.shtml

23. Q and A