EIGRP : EIGRP Routing Protocols and Concepts – Chapter 9
Objectives : 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
Key Terms : Key Terms Autonomous System
Loopback Address
Adjacency
Successor
Feasible Successor
Feasible Distance
Reported Distance
Passive/active state
History of EIGRP : History of 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
EIGRP Message Format : 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 – (more)
Type/Length/Values Fields - data portion of EIGRP message
EIGRP Message Format : EIGRP Message Format EIGRP packet header contains
Opcode field (packet type)
Autonomous System number
EIGRP Parameters contains
Weights
Hold time
Type Length Values (TLV) : Type Length Values (TLV) 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
Protocol Dependent Modules : Protocol Dependent Modules Protocol Dependent Modules or 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
Routes are calculated independently for each protocol
Reliable Transport Protocol (RTP) : 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’s 5 Packet Types : EIGRP’s 5 Packet Types Hello packets
Used to discover & form adjacencies with neighbors
EIGRP’s 5 Packet Types : EIGRP’s 5 Packet Types Update packets
Used to propagate routing information
Acknowledgement packets
Used to acknowledge receipt of update, query & reply packets
EIGRP’s 5 Packet Types : EIGRP’s 5 Packet Types Query & Reply packets
Used by DUAL for searching for networks
Query packets
-Can use
Unicast
Multicast
Reply packet
-Use only
unicast
EIGRP Keepalives : EIGRP Keepalives Purpose of Hello protocol (packet)
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 Bounded Updates : 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 Routing Algorithm : EIGRP Routing Algorithm 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 : 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 (redistributed)
EIGRP : EIGRP Authentication
EIGRP can
Encrypt routing information
Authenticate routing information
EIGRP : EIGRP Network Topology
Topology used is the same as previous chapters with the addition of an ISP router
Autonomous System Numbers : Autonomous System Numbers 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 providers
Institutions connecting to other institutions using AS numbers
Basic EIGRP Configuration : Basic EIGRP Configuration 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 : Basic EIGRP Configuration 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
Using an Inverse Mask with EIGRP : Using an Inverse Mask with EIGRP 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]
Viewing EIGRP Adjacencies (Neighbors) : Viewing EIGRP Adjacencies (Neighbors) 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 Verification : EIGRP Verification The show ip protocols command is also used to verify that EIGRP is enabled
Examining the Routing Table : 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
Null0 Summary Route : 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
Example of EIGRP Summarization : Example of EIGRP Summarization R3’s routing table shows that the 172.16.0.0/16 network is automatically summarized by R1 & R3
EIGRP Metric Calculation : EIGRP Metric Calculation EIGRP Composite Metric & the K Values
EIGRP uses the following values in its composite metric
-Bandwidth, delay, reliability, and load (and MTU)
The composite metric used by EIGRP
formula used has values K1 K5
K1 & K3 = 1
all other K values = 0
EIGRP Metric Calculation : EIGRP Metric Calculation Use the sh ip protocols command to verify the K values
EIGRP Metric Calculation : EIGRP Metric Calculation 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 1.544Mbps (T1)
EIGRP Metric Calculation : 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 : 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
Changing Metric Calculation : Changing 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 : EIGRP Metric Calculation The EIGRP metric can be determined by examining the
bandwidth delay
DUAL Concepts : DUAL Concepts The Diffusing Update Algorithm (DUAL) is used to prevent looping
DUAL Concepts : 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 : DUAL Concepts Feasible Successor
-This is a loop free backup route to same
destination as successor route Reported distance (RD)
-The metric that a router reports to a neighbor about its own cost to that network
DUAL Concepts : DUAL Concepts Feasibility Condition (FC)
-Met when a neighbor’s RD is less than the local router’s FD to the same destination network
Reported versus Feasible Distance : Reported versus Feasible Distance Reported Distance (by next hop router)
B reports 10 to Net X
C reports 10 to Net X
D reports 25 to Net X Feasible DistanceAdds link cost to next hop
Add 10 to C’s Reported Distance for a feasibility of 20 (C has the best overall metric) What is the best route from Router E to Net X?
EIGRP Topology Table : EIGRP Topology Table
Finite Sate Machine (FSM) : Finite Sate Machine (FSM) DUAL FSM
Selects a best loop-free path to a destination
Selects alternate routes by using information in EIGRP tables
Finite State Machines (FSM) Example : Finite State Machines (FSM) Example To examine output from EIGRP’s finite state machine us the debug eigrp fsm command
Disabling Automatic Summarization : 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
Manual Summarization : 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
Example: ip summary-address eigrp 1 192.168.16.0 255.255.240.0
EIGRP Default Routes : 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
Fine-Tuning EIGRP : Fine-Tuning EIGRP EIGRP bandwidth utilization
-By default, EIGRP uses 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
Configuring EIGRP Timers : Configuring EIGRP Timers Configuring Hello Intervals and Hold Times
-Hello intervals and hold times are configurable on a per-interface basis
-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
-Command to configure hold time value is
Router(config-if)#ip hold-time eigrp as-number seconds
Chapter 9 Labs : Chapter 9 Labs Lab 9.6.1 Basic EIGRP Configuration
Lab 9.6.2 Challenge EIGRP Configuration
Lab 9.6.3 EIGRP Troubleshooting
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