Routing Protocols and Concepts: Chapter 3 docx

Topics @ Introduction to EIGRP @ EIGRP Metric Calculation EIGRP: An Enhanced Distance Vector Routing Protocol EIGRP Message Format Protocol-Dependent Modules RTP and EIGRP Packet Types

Chapter 9

EIGR

stfect}ee

cisco

Routing Protocols and Concepts

CCNA Exploration Companion Guide

Rlck Grazlani « Allan Johnson Cisco Networking Academy”

Mind Wide Open™

For further information

This presentation is an

overview of what Is

covered in the

curriculum/book

For further explanation

and details, please read

Topics

@ Introduction to EIGRP @ EIGRP Metric Calculation

EIGRP: An Enhanced Distance Vector Routing Protocol

EIGRP Message Format Protocol-Dependent Modules RTP and EIGRP Packet Types Hello Protocol

EIGRP Bounded Updates DUAL: An Introduction Administrative Distance Authentication

@ Basic EIGRP Configuration

EIGRP Network Topology Autonomous Systems and Process IDs

The router eigro Command The network Command Verifying EIGRP

Examining the Routing Table

EIGRP Composite Metric and the K Values

EIGRP Metrics Using the bandwidth Command Calculating the EIGRP Metric

@ DUAL

DUAL Concepts

Successor and Feasible Distance

Feasible Successors, Feasibility Condition, and Reported Distance Topology Table: Successor and

Feasible Successor

Topology Table: No Feasible Successor

Finite State Machine

@ More EIGRP Configurations

The Null0 Summary Route Disabling Automatic Summarization Manual Summarization

EIGRP Default Route Fine- Tuning EIGRP

Introduction to EIGRP

@ EIGRP: An Enhanced Distance Vector Routing Protocol

@ EIGRP Message Format

e Classless routing protocol

@® Released in 1992 with Cisco IOS Software Release 9.21

@® Enhancement of Cisco Interior Gateway Routing Protocol (IGRP)

@® Both are Cisco proprietary

° Operate only on Cisco routers.

° Misleading, not a hybrid between distance vector and link-state

° Solely a distance vector routing protocol.

Keeps track of only the best routes; the best

path to a destination network

When a route becomes unavailable, the

router must wait for a new routing update

Maintains a topology table separate from the routing table, which includes the best path and any loop-free backup paths

When a route becomes unavailable, DUAL

uses a backup path if one exists in the topol-

@ Instead of hop count, both IGRP and EIGRP use metrics composed

of bandwidth, delay, reliability, and load

° Only bandwidth and delay are used by default.

EIGRP Message Format

Data Link Frame IP Packet EIGRP Packet

Header Header erie Type/Length/Values Types

IP Source Address = Address of Sending Interface

IP Destination Address = Multicast: 224.0.0.10 Protocol Field = 88 for EIGRP

EIGRP Packet Header

Opcode for EIGRP Packet Type

EIGRP Header field

Data field = Type/Length/Value, or TLV

Encapsulated in an IP packet

Protocol field = 88 (EIGRP)

Destination IP address = multicast 224.0.0.10

lf the EIGRP packet is encapsulated in an Ethernet frame: Destination MAC, multicast address: 01-00-5E-00-00-0A

EIGRP Message Format

* Opcode: EIGRP Packet Type: Update (1), Query (3), Reply (4), Hello (5)

* Autonomous System Number: ID for this EIGRP routing process

@® Opcode specifies the EIGRP packet type as one of the following:

° Update

° Query

° Reply

° Hello

EIGRP Packet Header Message Format

* Opcode: EIGRP Packet Type: Update (1), Query (3), Reply (4), Hello (5)

* Autonomous System Number: ID for this EIGRP routing process

Autonomous system number

° Specifies the EIGRP routing process

e Unlike RIP, Cisco routers can run multiple instances of EIGRP

@ EIGRP packet types are discussed later in this chapter

10

EIGRP TLV Message Format

Data Link Type/Length/Values Types:

* K1 and K3: Weights for bandwidth and delay; set to 1

* Hoki Time: Maximum time router shoukd wait for the next hello

@ EIGRP uses weights for its composite metric

¢ Set to 1

e Other K values are set to 0 (affect load and reliability)

® The hold time

e Amount of time the EIGRP neighbor receiving this message should wait before considering the advertising router to be down

e More later

* Delay: Sum of delays in units of 10 microseconds from source to destination;

OxFFFFFFFF indicates unreachable route

* Bandwidth: Lowest configured bandwidth of any interface along the route

+ Prefix Length: Specifies the number of network bits in the subnet mask

+ Destination: The destination address of the route

@ Metric fields:

® Subnet mask field (Prefix Length):

@ Destination field:

IP Packet Header | EIGRP Packet Header

* Delay: Sum of delays in units of 10 microseconds from source to destination;

OxFFFFFFFF indicates unreachable route

+ Bandwidth: Lowest configured bandwidth of any interface along the route

* Prefix Length: Specifies the number of network bits in the subnet mask

* Destination: The destination address of the route

@ Some EIGRP literature might incorrectly state that the maximum

transmission unit (MTU) is one of the metrics used by EIGRP

@ MTU Is not a metric used by EIGRP

® The MTU is included in the routing updates, but it is not used to

determine the routing metric

14

Destination1 Destination2

@ Example The IP-EIGRP module is responsible for:

° Sending and receiving EIGRP packets that are encapsulated in IP

15

RTP and EIGRP Packet Types

Reliable Transport Protocol (RTP)

Delivery and reception of EIGRP packets

Cannot use the services of UDP or TCP

Protocol Dependent Modules

Network-Layer Encapsulation

IPX and AppleTalk do not use protocols from the TCP/IP protocol suite

packets:

RTP includes both reliable delivery and unreliable delivery of EIGRP

Reliable RTP requires an acknowledqment (like TCP)

Unreliable RTP does not require an acknowledgment (like UDP)

Form adjacencies with those neighbors

@ EIGRP hello packets:

multicasts

unreliable delivery

17

EIGRP uses triggered

EIGRP Packet updates —a

Contains only the routing information needed (a change occurs)

Sent only to those routers that require it

Uses reliable delivery

e Multicast when sent to multiple routers

¢ Unicast when sent to a single router

@ Acknowledgment (ACK) Packets

sent when reliable delivery is used (update, query, and reply

packets)

* Used by DUAL when searching for networks or other tasks Reply packet

* Automatically sent in response to query packet acknowledgement (ACK) packet

- Automatically sent back when reliable RTP is used

@ Used by DUAL when searching for networks and other tasks

® Queries and replies use reliable delivery

TO Keep this example simple, acknowledgments were omitted in the

graphic

All neighbors must send a reply regardless of whether they have a route

to the downed network

@® (Queries can use multicast or unicast, whereas replies are always sent as

unicast

@ DUAL is discussed in a later section

Hello Protocol -

® Decfore any EIGRP packets can be exchanged between routers,

EIGRP must first discover its neighbors

@ EIGRP routers discover neighbors and establish adjacencies with

neighbor routers using the hello packet

20

Hello Protocol

@ Most networks, EIGRP hello packets are sent every 5 seconds

@ On multipoint nonbroadcast multiaccess (NBMA) networks such as

X.25, Frame Relay, and ATM interfaces with access links of T1 (1.544

Mbps) or slower, hellos are unicast every 60 seconds

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

a neighbor, the neighbor and its routes remain viable

21

Default Hello Default Hold

@® Hold time - maximum time the router should wait to receive the

next hello before declaring that neighbor as unreachable

@® Default hold time - 3 times the hello interval,

15 seconds on most networks

180 seconds on low-speed NBMA networks

® lf the hold time expires:

EIGRP declares the route as down DUAL searches for a new path in the topology table or by sending out queries

@ EIGRP uses the terms partial and bounded when referring to its

update packets

@ EIGRP sends its updates only when the metric for a route changes

The term partial means that the update only includes information

about the route changes

The term bounded refers to the propagation of partial updates

sent only to those routers that are affected by the change

@ This minimizes the bandwidth required to send EIGRP packets

23

J J Garcia-Luna-Aceves

Diffusing Update Algorithm (DUAL) is the convergence algorithm used by

EIGRP

First proposed by E W Dijkstra and C S Scholten

The most prominent work with DUAL has been done by J J Garcia-Luna-

Aceves

Routing loops, even temporary ones, can be extremely detrimental to

network performance

Distance vector routing protocols such as RIP prevent routing loops with

hold-down timers and split horizon

Although EIGRP uses both of these techniques, it uses them somewhat

differently; the primary way that EIGRP prevents routing loops is with the

DUAL algorithm “4

DUAL: An Introduction

1 A directly connected network on R2 goes down

R2 sends an EIGRP update message to its neighbors indicating the network is down

2 Ri and R3 return an EIGRP acknowledgment indicating that they

have received the update from R2

20

5 R1 and R3 send an EIGRP reply message in response to the query sent by R2

In this case, the reply would state that the router does not have a route to this network

6 R2 returns an acknowledgment indicating that it received the reply

Note: Much more later! z6

Administrative Distance

@ When compared to other

interior gateway protocols

(IGP), EIGRP is the most

preferred by the Cisco IOS

software because it has the

lowest AD

@ Later in this chapter, you

learn how to configure EIGRP

Authentication

Like other routing protocols, EIGRP can be configured for authentication

lt is good practice to authenticate transmitted routing information

This practice ensures that routers will accept routing information only from

other routers that have been configured with the same password or

authentication information

When authentication is configured on a router, the router authenticates the

source of each routing update packet that it receives

Basic EIGRP Configuration

@ EIGRP Network Topology

@ Autonomous Systems and Process IDs

® The router eigro Command

@® The network Command

® Verifying EIGRP

@® Examining the Routing Table

@ Includes the addition of the ISP router

@ Ri and R2 routers have subnets that are part of the 172.16.0.0/16

@ ISP router does not physically exist in our configurations

@ The connection between R2 and ISP is represented with a loopback

ISP1: AS 64515

Autonomous system Company A: EIGRP Company B: OSPF

and Process IDs

common routing policy to |

the Internet \

Described in RFC

1930

@ AS numbers are assigned

by IANA and its RIR Company C: EIGRP

autonomous system a>"

number because they

come under the control of

a larger entity such as an

Both EIGRP and OSPF use a process [D to represent an instance of their

respective routing protocol running on the router

Although EIGRP refers to the parameter as an “auftonomous-system”

number, it actually functions as a process ID

AS parameter is between 1 and 65,535

All routers in this EIGRP routing domain must use the same _process |D

number (autonomous system number)

36

The router eigrp

Router (config-router) # network network-address

® The network command in EIGRP has the same function as in other

IGP routing protocols:

Any interface on this router that matches the network address In

the network command will be enabled to send and receive

EIGRP updates

This network (or subnet) will be included in EIGRP routing

® The network-address ts the classful network address for this interface

® 172.16.0.0 includes both 172.16.1.0/24 and 172.16.3.0/30 subnets

@ When EIGRP is configured on R2, DUAL sends a notification message to

the console stating that a neighbor relationship with another EIGRP router

has been established

@® This new adjacency happens automatically because both R1 and R2 are

using the same EIGRP 1 routing process and both routers are now sending

updates on the 172.16.0.0 network 39

@ Network command — When uses classful network address:

All interfaces on the router that belong to that classful network address will be enabled for EIGRP

@ To include only specific interface(s), subnets, to be enabled for EIGRP:

Use the wildcard-mask option

40

The network Command with a Wildcard Mask

R2(config-router)# network 192.168.10.8 0.0.0.3

Or

R2(config-router)# network 192.168.10.8 255.255.255.252

Think of a wildcard mask as the inverse of a subnet mask

The inverse of subnet mask 255.255.255.252 is 0.0.0.3

To calculate the inverse of the subnet mask, subtract the subnet mask from

The network Command with a Wildcard Mask

The network 172.18.2.0/24

Command with a Đi

Wildcard Mask \ + ÍFaoo

10 192.168.10.8/30

R2(config-router) # network 192.168.10.8 0.0.0.3

@ The passive-interface command should not be used with EIGRP

@ When the passive-interface command is configured, EIGRP stops sending

hello packets on that interface

Will not form an adjacency Unable to send or receive routing updates

.168.1.0 168.10.0 44

Verifying EIGRP

R2#show ip eigrp neighbors

IP-EIGRP neighbors for process 1

Address of Neighbors Interface Connected Amount of Time

to Neighbor Since Adjacency Was

Established

Amount of Time Left

Before Neighbor Is

Considered “Down”

@ EIGRP routers must first establish adjacencies with their neighbors before

any updates can be sent or received

® show ip eigrp neighbors - view the neighbor table and verify that

adjacencies with its neighbors

® lf aneighbor is not listed:

° Check the local interfaces to make sure it is activated with the show ip interface brief command