BSCI Module 2-Lesson 1-Edited

© 2006 Cisco Systems, Inc. All rights reserved. Cisco ConfidentialBSCI 2 - 1 1

Configuring EIGRP

BSCI Module 2-1 – Introduction to EIGRP


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


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.


EIGRP Features

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


EIGRP Key Technologies

Neighbor discover/recovery

Reliable Transport Protocol (RTP)

DUAL finite-state machine

Protocol-dependent modules (PDMs)


The Diffusing Update Algorithm (DUAL)

How does EIGRP determine which routes are loop-free?

B with a cost of 10

Each of A’s neighbors is reporting reachability to E:

C with a cost of 10D with a cost of 30

These three costs are called the reported distance (RD); the distance each neighbor is reporting to a given destination



At A, the total cost to reach E is:

The best of these three paths is the path through B, with a cost of 20

20 through B

25 through C

45 through D

This is the feasible distance (FD)



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



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.


EIGRP Topology Table


RTRA#show ip eigrp neighborsIP-EIGRP neighbors for process 1H Address Interface Hold Uptime SRTT RTO Q Seq (sec) (ms) Cnt Num2 10.1.1.1 Et0 12 6d16h 20 200 0 2331 10.1.4.3 Et1 13 2w2d 87 522 0 4520 10.1.4.2 Et1 10 2w2d 85 510 0 3

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


EIGRP IP Routing Table


Example: EIGRP TablesRouter C’s tables:


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


Initial Route Discovery


EIGRP Metric Same metric components as IGRP:

Bandwidth

Delay

Reliability

Loading

MTU

EIGRP metric is IGRP metric multiplied by 256


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)]


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


EIGRP Metrics Are Backward-Compatible with IGRP


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.


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? __________, _________, _________, __________, ___________


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


Q and A


Documents

BSCI Module 2-Lesson 1-Edited