Module 2- Lesson 1&2 – Introduction to EIGRP pptx

 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 f

BSCI Module 2- Lesson 1&2 – Introduction to EIGRP

 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

The Evolution of Dynamic Routing Protocols

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BSCI

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Dynamic Routing Protocols Classification

IGP and EGP

 An autonomous system (AS) - otherwise known as a routing

domain - is a collection of routers under a common administration

 Two types of routing protocols are: interior and exterior routing

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BSCI

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Distance Vector and Link State

 Interior Gateway Protocols (IGPs) can be classified as two types:

–Distance vector routing protocols

–Link-state routing protocols

Distance Vector Routing Protocol Operation

 Distance vector means that routes are advertised as vectors of

distance and direction

–Distance is defined in terms of a metric such as hop count

–Direction is simply the next-hop router or exit interface

–Algorithm is Bellman-Ford

Distance Vector and Link State

 Distance Vector Routing Protocol Features:

–The network is simple and flat and does not require a special hierarchical design

–The administrators do not have enough knowledge to configure and troubleshoot link-state protocols

–Specific types of networks, such as hub-and-spoke networks, are being implemented

–Worst-case convergence times in a network are not a concern

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Distance Vector and Link State

Link-state Protocol Operation

 A link-state router uses the link-state information to create a topology

map and to select the best path to all destination networks in the

topology

 Link-state protocols Features:

–The network design is hierarchical, usually occurring in large

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

Hybrid Cisco Routing Protocol

EIGRP Features

EIGRP Key Technologies

Protocol-dependent Modules

–Sending and receiving EIGRP packets that are encapsulated

–Redistributing routes learned by other IP routing protocols

 Each protocol has its

own EIGRP module

and operates

independently from

any of the others that

may be running

 EIGRP is protocol-independent; that is, it doesn’t rely on TCP/IP to

exchange routing information the way RIP, IGRP, and OSPF do

 To stay independent of IP, EIGRP uses the transport-layer protocol to

guarantee delivery of routing information: RTP

 RTP supports reliable and unreliable delivery

 RTP supports unicasting and multicasting

 Initial delivery of EIGRP messages are done using multicast packets, that is

data is sent to all neighbors on a segment, and every neighbor is expected to

acknowledge it with a unicast Hello packet.

 After adjacency has been formed and added to neighbor table, routers

exchange routing information which is stored in the topology table (later)

 RTP is used for EIGRP queries, updates and replies

 RTP is not used for EIGRP Hello’s and Ack’s

Reliable Transport Protocol

Initial Route Discovery

 Identify the four key steps of EIGRP operation

Activity Answer

 DUAL selects alternate routes quickly by using the information in the EIGRP

tables

 If a link goes down, DUAL looks for a feasible successor in its neighbor and

topology tables.

 A successor is a neighboring router that is currently being used for packet

forwarding, provides the least-cost route to the destination, and is not part of a

routing loop.

 Feasible successors provide the next lowest-cost path without introducing

routing loops

– Feasible successor routes can be used in case the existing route fails;

packets to the destination network are immediately forwarded to the feasible successor, which at that point, is promoted to the status of successor.

 Selects a best loop-free path to a destination, the next hop being known as the

The Diffusing Update Algorithm (DUAL)

which routes are loop-free?

 These three costs are

called the reported distance (RD); the distance each neighbor is reporting to a given

destination

The Diffusing Update Algorithm (DUAL)

 At A, the total cost to reach

E is:

 The best of these three

paths is the path through

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

The Diffusing Update Algorithm (DUAL)

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

Example from the curriculum…

Example from the curriculum…

7

EIGRP Tables

RTRA# show ip 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

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 Topology Table

EIGRP Topology Table

EIGRP IP Routing Table

EIGRP Routing Table

Example: EIGRP Tables

Router 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

Establishing Adjacencies with Neighbors

 EIGRP routers establish adjacencies with neighbor routers by using small

hello packets

 Hellos are sent every 5s(BW>1,544M) and 60s(BW=<1,544M)by default

 K values must be the same between neighbors.

 An EIGRP router assumes that, as long as it is receiving hello packets from

known neighbors, those neighbors (and their routes) remain viable.

 Hold time tells the router how long it should consider the neighbor alive if it has

not received any EIGRP packets (Hello, EIGRP updates, etc.)

 Hold time is normally three times the configured Hello interval.

 Both the Hello and Hold time intervals are configurable on a per interface

basis, and do not have to match neighbor.

 EIGRP routers exchange routing information the same way as other distance

vector routing protocols, but do not send periodic updates.

 EIGRP updates are only sent when a network is added or removed from the topology database, when the successor for a given network changes, or when

the locally used metric is updated (later)

Hello Intervals and Default Hold Times

 Hello Time The interval of Hello Packets

 Hold Time The interval to wait without receiving anything from a

neighbor before considering the link unavailable

EIGRP Metric

–Bandwidth: Smallest bandwidth between source and

destination

–Delay: Cumulative interface delay along the path

–Reliability: Worst reliability between source and destination,

based on keepalives

–Loading: Worst load on a link between source and

destination, based on the packet rate and the configured bandwidth of the interface

–MTU: Smallest MTU in the path MTU is included in the

EIGRP routing update, but is not actually used in the metric calculation

 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,

Metric Calculation (Review)

EIGRP

– k1 for bandwidth – k2 for load

– k3 for delay – k4 and k5 for Reliability

Router(config-router)# metric

View Bandwidth, Delay, Load, Reliability

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:

EIGRP Metrics Are Backward-Compatible with IGRP

IGRP and EIGRP: A migration path

32 bit metric for bandwidth and delay Maximum Hop Count = 255 Maximum Hop Count = 224

No differentiation between internal and

Condition to be neighbor

 Match K value

 Primary address on the same subnet

 Match authentication (if has)

 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

1 What is a reported distance?

2 What is a feasible distance?

3 EIGRP uses three tables: name the three tables: ,

, _ Which of the tables contains the best route or successor route to each destination?

4 EIGRP uses what metrics? , _,

_, , _