EIGRP

Objectives
Describe the background and history of Enhanced Interior Gateway Routing Protocol (EIGRP).
Examine the basic EIGRP configuration commands and identify their purposes.
Calculate the composite metric used by EIGRP.
Describe the concepts and operation of DUAL.
Describe the uses of additional configuration commands in EIGRP.

Introduction

EIGRP
Roots of EIGRP: IGRP
-Developed in 1985 to overcome RIPv1’s limited hop count
-Distance vector routing protocol
-Metrics used by IGRP
bandwidth (used by default)
Delay (used by default)
reliability
load
-Discontinued support starting with IOS 12.2(13)T & 12.2(R1s4)S

EIGRP
EIGRP Message Format
EIGRP Header
Data link frame header - contains source and destination MAC address
IP packet header - contains source & destination IP address
EIGRP packet header - contains AS number
Type/Length/Field - data portion of EIGRP message

EIGRP
EIGRP packet header contains
Opcode field
Autonomous System number
EIGRP Parameters contains
Weights
Hold time

EIGRP
TLV: IP internal contains
Metric field
Subnet mask field
Destination field
TLV: IP external contains
Fields used when external
routes are imported into
EIGRP routing process

EIGRP
Protocol Dependent Modules (PDM)
EIGRP uses PDM to route several different protocols i.e. IP, IPX & AppleTalk
PDMs are responsible for the specific routing task for each network layer protocol

EIGRP
Reliable Transport Protocol (RTP)
Purpose of RTP
Used by EIGRP to transmit and receive EIGRP packets
Characteristics of RTP
Involves both reliable & unreliable delivery of EIGRP packet
Reliable delivery requires acknowledgment from destination
Unreliable delivery does not require an acknowledgement from destination
Packets can be sent
Unicast
Multicast
Using address 224.0.0.10

EIGRP
EIGRP’s 5 Packet Types
Hello packets
Used to discover & form adjacencies with neighbors

EIGRP
Update packets
Used to propagate routing information
Acknowledgement packets
Used to acknowledge receipt of update, query & reply packets

EIGRP
Query & Reply packets
Used by DUAL for searching for networks
Query packets
-Can use
Unicast
Multicast
Reply packet
-Use only
unicast

EIGRP
Purpose of Hello Protocol
To discover & establish adjacencies with neighbor routers
Characteristics of hello protocol
Time interval for sending hello packet
Most networks it is every 5 seconds
Multipoint non broadcast multi-access networks
Unicast every 60 seconds
-Holdtime
This is the maximum time router should wait before declaring a neighbor down
Default holdtime
3 times hello interval

EIGRP
EIGRP Bounded Updates
EIGRP only sends update when there is a change in route status
Partial update
A partial update includes only the route information that has changed – the whole routing table is NOT sent
Bounded update
When a route changes, only those devices that are impacted will be notified of the change
EIGRP’s use of partial bounded updates minimizes use of bandwidth

EIGRP
Diffusing Update Algorithm (DUAL)
Purpose
EIGRP’s primary method for preventing routing loops
Advantage of using DUAL
Provides for fast convergence time by keeping a list of loop-free backup routes

EIGRP
Administrative Distance (AD)
Defined as the trustworthiness of the source route
EIGRP default administrative distances
Summary routes = 5
Internal routes = 90
Imported routes = 170

EIGRP
Authentication
EIGRP can
Encrypt routing information
Authenticate routing information

EIGRP
Network Topology
Topology used is the same as previous chapters with the addition of an ISP router

EIGRP
EIGRP will automatically summarize routes at classful boundaries

Basic EIGRP Configuration
Autonomous System (AS) & Process IDs
This is a collection of networks under the control of a single authority (reference RFC 1930)
AS Numbers are assigned by IANA
Entities needing AS numbers
ISP
Internet Backbone prodiers
Institutions connecting to other institutions using AS numbers

Basic EIGRP Configuration
EIGRP autonomous system number actually functions as a process ID
Process ID represents an instance of the routing protocol running on a router
Example
Router(config)#router
eigrp autonomous-system

Basic EIGRP Configuration
The router eigrp command
The global command that enables eigrp is
router eigrp autonomous-system
-All routers in the EIGRP routing domain must use the same process ID number (autonomous-system number)

Basic EIGRP Configuration
The Network Command
Functions of the network command
Enables interfaces to transmit & receive EIGRP updates
Includes network or subnet in EIGRP updates
Example
Router(config-router)#network network-address

Basic EIGRP Configuration
The network Command with a Wildcard Mask
-This option is used when you want to configure EIGRP to advertise specific subnets
-Example
Router(config-router)#network network-address [wildcard-mask]

Basic EIGRP Configuration
Verifying EIGRP
EIGRP routers must establish adjacencies with their neighbors before any updates can be sent or received
Command used to view neighbor table and verify that EIGRP has established adjacencies with neighbors is
show ip eigrp neighbors

EIGRP
The show ip protocols command is also used to verify that EIGRP is enabled

Basic EIGRP Configuration
Examining the Routing Table
The show ip route command is also used to verify EIGRP
EIGRP routes are denoted in a routing table by the letter “D”
By default , EIGRP automatically summarizes routes at major network boundary

Basic EIGRP Configuration
Introducing the Null0 Summary Route
Null0 is not a physical interface
In the routing table summary routes are sourced from Null0
Reason: routes are used for advertisement purposes
EIGRP will automatically include a null0 summary route as child route when 2 conditions are met
At least one subnet is learned via EIGRP
Automatic summarization is enabled

Basic EIGRP Configuration
R3’s routing table shows that the 172.16.0.0/16 network is automatically summarized by R1 & R3

EIGRP Metric Calculation
EIGRP Composite Metric & the K Values
EIGRP uses the following values in its composite metric
-Bandwidth, delay, reliability, and load
The composite metric used by EIGRP
formula used has values K1 ?K5
K1 & K3 = 1
all other K values = 0

EIGRP Metric Calculation
Use the sh ip protocols command to verify the K values

EIGRP Metric Calculation
EIGRP Metrics
Use the show interfaces command to view metrics
EIGRP Metrics
Bandwidth – EIGRP uses a static bandwidth to calculate metric
Most serial interfaces use a default bandwidth value of 1.544Mbos (T1)

EIGRP Metric Calculation
EIGRP Metrics
Delay is the defined as the measure of time it takes for a packet to traverse a route
-it is a static value based on link type to which interface is connected

EIGRP Metric Calculation
Reliability (not a default EIGRP metric)
-A measure of the likelihood that a link will fail
-Measure dynamically & expressed as a fraction of 255
the higher the fraction the better the reliability
Load (not a default EIGRP metric)
A number that reflects how much traffic is using a link
Number is determined dynamically and is expressed as a fraction of 255
The lower the fraction the less the load on the link

EIGRP Metric Calculation
Using the Bandwidth Command
Modifying the interface bandwidth
-Use the bandwidth command
-Example
Router(config-if)#bandwidth kilobits
Verifying bandwidth
Use the show interface command
Note – bandwidth command
does not change the
link’s physical
bandwidth

EIGRP Metric Calculation
The EIGRP metric can be determined by examining the
bandwidth delay

EIGRP Metric Calculation
EIGRP uses the lowest bandwidth (BW)in its metric calculation
Calculated BW = reference BW / lowest BW(kbps)
Delay – EIGRP uses the cumulative sum of all outgoing interfaces
Calculated Delay = the sum of outgoing interface delays
EIGRP Metric = calculated BW + calculated delay

EIGRP Metric Calculation

DUAL Concepts
The Diffusing Update Algorithm (DUAL) is used to prevent looping

DUAL Concepts
Successor
The best least cost route to a destination found in the routing table
Feasible distance
The lowest calculated metric along a path to a destination network

DUAL Concepts
Feasible Successors, Feasibility Condition & Reported Distance
Feasible Successor
-This is a loop free backup route to same
destination as successor route

DUAL Concepts
Reported distance (RD)
-The metric that a router reports to a neighbor about its own cost to that network
Feasible Successors, Feasibility Condition & Reported Distance

DUAL Concepts
Feasibility Condition (FC)
-Met when a neighbor’s RD is less than the local router’s FD to the same destination network

DUAL Concepts
Topology Table: Successor & Feasible Successor
EIGRP Topology table
Viewed using the show ip eigrp topology command
Contents of table include:
all successor routes
all feasible successor routes

DUAL Concepts
EIGRP Topology Table dissected

DUAL Concepts
Topology Table: No Feasible Successor
A feasible successor may not be present because the feasibility condition may not be met
-In other words, the reported distance of the neighbor is greater than or equal to the current feasible distance

DUAL Concepts
Finite Sate Machine (FSM)
An abstract machine that defines a set of possible states something can go through, what event causes those states and what events result form those states
FSMs are used to describe how a device, computer program, or routing algorithm will react to a set of input events

DUAL Concepts
DUAL FSM
Selects a best loop-free path to a destination
Selects alternate routes by using information in EIGRP tables

DUAL Concepts
Finite State Machines (FSM)
To examine output from EIGRP’s finite state machine us the debug eigrp fsm command

More EIGRP Configurations
The Null0 Summary Route
By default, EIGRP uses the Null0 interface to discard any packets that match the parent route but do not match any of the child routes
EIGRP automatically includes a null0 summary route as a child route whenever both of the following conditions exist
One or subnets exists that was learned via EIGRP
Automatic summarization is enabled

More EIGRP Configurations
The Null0 Summary Route

More EIGRP Configurations
Disabling Automatic Summarization
The auto-summary command permits EIGRP to automatically summarize at major network boundaries
The no auto-summary command is used to disable automatic summarization
This causes all EIGRP neighbors to send updates that will not be automatically summarized
this will cause changes to appear in both
-routing tables
-topology tables

More EIGRP Configurations
Manual Summarization
Manual summarization can include supernets
Reason: EIGRP is a classless routing protocol & include subnet mask in update
Command used to configure manual summarization
Router(config-if)#ip summary-address eigrp as-number network-address subnet-mask

More EIGRP Configurations
Configuring a summary route in EIGRP

More EIGRP Configurations
EIGRP Default Routes
“quad zero” static default route
-Can be used with any currently supported routing protocol
-Is usually configured on a router that is connected a network outside the EIGRP domain
EIGRP & the “Quad zero” static default route
Requires the use of the redistribute static command to disseminate default route in EIGRP updates

More EIGRP Configurations
Fine-Tuning EIGRP
EIGRP bandwidth utilization
-By default, EIGRP uses only up to 50% of interface bandwidth for EIGRP information
-The command to change the percentage of bandwidth used by EIGRP is
Router(config-if)#ip bandwidth-percent eigrp as- number percent

More EIGRP Configurations
Configuring Hello Intervals and Hold Times
-Hello intervals and hold times are configurable on a per-interface basis
-The command to configure hello interval is
Router(config-if)#ip hello-interval eigrp as-number seconds
Changing the hello interval also requires changing the hold time to a value greater than or equal to the hello interval
-The command to configure hold time value is
Router(config-if)#ip hold-time eigrp as-number seconds

Summary
Background & History
EIGRP is a derivative of IGRP
EIGRP is a Cisco proprietary distance vector routing protocol released in 1994
EIGRP terms and characteristics
EIGPR uses RTP to transmit & receive EIGRP packets
EIGRP has 5 packet type:
Hello packets
Update packets
Acknowledgement packets
Query packets
Reply packets
Supports VLSM & CIDR

Summary
EIGRP terms and characteristics
EIGRP uses a hello protocol
Purpose of hello protocol is to discover & establish adjacencies
EIGRP routing updates
Aperiodic
Partial and bounded
Fast convergence

Summary
EIGRP commands
The following commands are used for EIGRP configuration
RtrA(config)#router eigrp [autonomous-system #]
RtrA(config-router)#network network-number
The following commands can be used to verify EIGRP
Show ip protocols
Show ip eigrp neighbors
Show ip route

Summary
EIGRP metrics include
Bandwidth (default)
Delay (default)
Reliability
Load

Summary
DUAL
Purpose of DUAL
To prevent routing loops
Successor
Primary route to a destination
Feasible successor
Backup route to a destination
Feasible distance
Lowest calculated metric to a destination
Reported distance
The distance towards a destination as advertised by an upstream neighbor

Summary
Choosing the best route
After router has received all updates from directly connected neighbors, it can calculate its DUAL
1st metric is calculated for each route
2nd route with lowest metric is designated successor & is placed in routing table
3rd feasible successor is found
Criteria for feasible successor: it must have lower reported distance to the destination than the installed route’s feasible distance
Feasible routes are maintained in topology table

Summary
Automatic summarization
On by default
Summarizes routes on classful boundary
Summarization can be disabled using the following command
RtrA(config-if)#no auto-summary