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Chapter 9: EIGRP
CCNA Ex loration version 4.0
1
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Objectives
Describe the background and history of EnhancedInterior Gateway Routing Protocol (EIGRP).
Examine the basic EIGRP configuration commandsand identify their purposes.
Calculate the composite metric used by EIGRP.
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Describe the concepts and operation of DUAL. Describe the uses of additional configuration
commands in EIGRP.
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Introduction to EIGRP
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EIGRP
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e ma n purpose n sco s eve opmen o was o crea e a c ass essversion of IGRP.
EIGRP includes several features that are not commonly found in other distancevector routing protocols like RIP (RIPv1 and RIPv2) and IGRP.
These features include:1. Reliable Transport Protocol (RTP)
2. Bounded Updates3. Diffusing Update Algorithm (DUAL)4. Establishing Adjacencies5. Neighbor and Topology Tables
Although EIGRP may act like a link-state routing protocol, it is still a distance
vector routing protocol.
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EIGRP
Roots of EIGRP: IGRP Developed in 1985 to overcome
RIPv1s limited hop count Distance vector routing protocol
Metrics used by IGRP
bandwidth (used by default)
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delay (used by default) reliability
load
Discontinued support starting with
IOS 12.2(13)T & 12.2(R1s4)S
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IGRP to EIGRP
Enhanced Distance Vector RoutingProtocol: EIGRP
Uses the Diffusing Update Algorithm
(DUAL) Does not age out routing entries noruses periodic updates.
Maintains a topology table separate
Traditional Distance VectorRouting Protocols
Use the Bellman-Ford orFord-Fulkerson algorithm.
Age out routing entries anduses periodic updates.
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,
includes the best path and any loop-free backup paths.
When a route becomes unavailable,DUAL will use a backup path if oneexists in the topology table.
Faster convergence due to theabsence of holddown timers and asystem of coordinated routecalculations.
routes; the best path to adestination network.
When a route becomesunavailable, the router must
wait for a new routingupdate.
Slower convergence due toholddown timers.
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EIGRP Capabilities and Attributes
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EIGRP Message Format
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The data portion of an EIGRP message is encapsulated in a packet.This data field is called Type/Length/Value or TLV.
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The Autonomous System (AS)Number specifies the EIGRProuting process.
Unlike RIP, Cisco routerscan run multi le instances of
EIGRP Message Format
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EIGRP. The AS number is used to
track multiple instances of
EIGRP.
EIGRP Parameters contains Weights
Hold time
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TLV: IP internal contains Metric field
EIGRP Message Format
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u ne mas e
Destination field
TLV: IP external contains Fields used when external
routes are imported intoEIGRP routing process
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Protocol Dependent Modules (PDM)
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RTP and EIGRP Packet Types
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Purpose of RTP: to transmit and receive EIGRPpackets
Characteristics of RTPInvolves both reliable & unreliable delivery of
EIGRP packet
RTP and EIGRP Packet Types
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Reliable delivery requires acknowledgment fromdestination
Unreliable delivery does not require an
acknowledgement from destinationPackets can be sent
Unicast
Multicast : Using address 224.0.0.10
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RTP and EIGRP Packet Types
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RTP and EIGRP Packet Types
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Hello Protocol
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RTP and EIGRP Packet Types
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RTP and EIGRP Packet Types
Update packetsUsed to propagate routing information
Update packets are sent as amulticast when required by multiple
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,by only a single router.
Acknowledgement packets
Used to acknowledge receipt ofupdate, query & reply packetsEIGRP acknowledgement packets are
always sent as an unreliable unicast.
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RTP and EIGRP Packet Types
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RTP and EIGRP Packet Types
Query & Reply packets
Used by DUAL for searching fornetworks
uer ackets: can use:
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Unicast
Multicast
Reply packet: use only
unicast
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EIGRP Bounded Updates
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EIGRPs use of partial boundedupdates minimizes use of bandwidth
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Diffusing Update Algorithm (DUAL)
Purpose:EIGRPs primary method for
DUAL: An Introduction
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preventing routing loopsAdvantage:
Provides for fast convergencetime by keeping a list of loop-
free backup routes
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Administrative Distance
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Authentication
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Note: Authentication does not encrypt the
router's routing table
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Basic EIGRP Configuration
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EIGRP Network Topology
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Network Topology
Topology used is the same as previous chapters with
the addition of an ISP router
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An autonomous system (AS) is a collectionof networks under the administrativecontrol of a single entity that presents acommon routing policy to theInternet.(reference RFC 1930)
Autonomous System and Process IDs
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Entities needing AS numbers ISP Internet Backbone providers Institutions connecting to other
institutionsusing AS numbers
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Autonomous System and Process IDs
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EIGRPautonomous
system numberactually functionsas a process ID
Autonomous System and Process IDs
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Process IDrepresents aninstance of the
routing protocolrunning on a router
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The router eigrpCommand
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All routers in the EIGRP routing domainmust use the same process ID number(autonomous-system number)
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The networkCommand
Directly connected classful address
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Functions of the network commandEnables interfaces to transmit & receive EIGRP
updates
Includes network or subnet in EIGRP updates
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The networkCommand
Router(config-router)#network network-address [wildcard-mask]
This option is used when you want to configure
EIGRP to advertise specific subnets
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EIGRP routers must establish adjacencies with their neighbors beforeany 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
Verifying EIGRP
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If any packet is reliably multicast and an ACK is not received from a neighbor,the packet will be retransmitted as a unicast to that unresponding neighbor.
If an ACK is not received after16of these unicast retransmissions, theneighbor will be declared dead.
The time to wait for an ACK before switching from multicast to unicast isspecified by themulticast flowtimer.
Smooth Round Trip Timer (SRTT): the average elapsed time, measured inmilliseconds between the transmission of a acket to the nei hbor and the
Extra: Neighbor Table
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receipt of an acknowledgment.
This timer is used to determine the retransmit interval (RTO) The RTO is the time, in milliseconds, that the router will wait for an
acknowledgment of a unicast packet sent after a multicast has failed.
Hold Time The interval to wait without receiving anything from a neighbor
before considering the link unavailable. Originally, the expected packet was a hello packet, but in current Cisco IOSsoftware releases, any EIGRP packets received after the first hello will resetthe timer.
The formulas for calculating the exact values of the SRTT, the RTO, and themulticast flow timer are proprietary.
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RouterC#show ip eigrp neighbors
IP-EIGRP neighbors for process 44
H Address Interface Hold Uptime SRTT RTO Q Seq
(sec) (ms) CntNum
0 192.168.0.1 Se0 11 00:03:09 1138 5000 0 6
1 192.168.1.2 Et0 12 00:34:46 4 200 0 4
Extra: Neighbor Table
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Neighbor address:The network-layer address of the neighborrouter(s). Queue count:The number of packets waiting in queue to be sent. If
this value is constantly higher than zero, then there may be a
congestion problem at the router. A zero means that there are noEIGRP packets in the queue.
Sequence Number:The number of last packet that is received fromthat neighbor. EIGRP uses this field to acknowledge a neighborstransmission and to identify packets that are out of sequence.
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The show ip protocolscommand is used to verify that EIGRP is enabled
Verifying EIGRP
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Examining the Routing Table
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By default ,
EIGRPautomaticallysummarizes
Examining the Routing Table
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routes atmajornetwork
boundary
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Introducting the Null0 Summary Route
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Null0 is not a physical interface In the routing table summary routes are
sourced from Null0 Reason: routes are used for
advertisement ur oses
Introducting the Null0 Summary Route
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EIGRP will automatically include a null0summary route as child route when 2conditions are met:
1. At least one subnet is learned viaEIGRP2. Automatic summarization is
enabled
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Examining the Routing Table
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au o-summary
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EIGRP Metric Calculation
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EIGRP M t i C l l ti
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EIGRP Metric Calculation
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EIGRP C it M t i d th K V l
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Use the show ip protocols command to verify the Kvalues
EIGRP Composite Metric and the K Values
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EIGRP Metric Calculation
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Use the showinterfaces commandto view metrics
Bandwidth EIGRPuses a static
EIGRP Metric Calculation
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calculate metric Most serial interfaces
use a defaultbandwidth value of1.544Mbos (T1)
EIGRP Metric Calculation
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EIGRP Metric Calculation
Delay
Delay is the
defined as themeasure of time ittakes for a packet
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to traverse a route it is a static valuebased on link type
to which interfaceis connected
EIGRP Metric Calculation
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EIGRP Metric Calculation
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EIGRP Metric Calculation
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Reliability (not a default EIGRP metric)A measure of the likelihood that a link will fail
Measure dynamically & expressed as a fractionof 255 the higher the fraction the better thereliability
EIGRP Metric Calculation
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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 255The lower the fraction the less the load on the
link
EIGRP Metric Calculation
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Router(config-if)#bandwidthkilobits
Note bandwidthcommand does not
EIGRP Metric Calculation
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physical bandwidth
EIGRP Metric Calculation
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EIGRP Metric Calculation
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EIGRP Metric Calculation
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EIGRP Metric Calculation
EIGRP uses the lowest bandwidth (BW) in itsmetric calculation:
Calculated BW = (reference BW / lowest BW(kbps)*256(reference BW = 107 )
Dela EIGRP uses the cumulative sum of all
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outgoing interfaces:Calculated Delay = (the sum of outgoing interface delays/10)*256
EIGRP Metric = calculated BW + calculateddelay
EIGRP Metric Calculation
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EIGRP Metric Calculation
Calculate the metric from R2 to 192.168.1.0/24
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Determining the costs
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S0/0 192.168.64.2/30 S0/1 192.168.64.6/30
Fa0/0 192.168.72.1/24
Calculated Bandwidth = (10,000,000/bandwidth kbps) * 256
Westasman
Bandwidth =
25,600
Delay =
2,560FastEthernet
= (10,000,000/100,000) * 256
= 25,600
T1
*
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S0/0 192.168.64.1/30 S0/0 192.168.64.5/30
Fa0/0 192.168.1.1/24
Fa0/0 192.168.1.2/24
EIGRP
AS 100
SanJose1SanJose2
Bandwidth =
1,657,856
=
512,000
= , ,
= 1,657,856
Determining the costs
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S0/0 192.168.64.2/30 S0/1 192.168.64.6/30
Fa0/0 192.168.72.1/24
Calculated Delay = (delay/10) * 256
Westasman
Bandwidth =
25,600
Delay =
2,560FastEthernet
= (100/10) * 256
= 2,560
T1
*
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S0/0 192.168.64.1/30 S0/0 192.168.64.5/30
Fa0/0 192.168.1.1/24
Fa0/0 192.168.1.2/24
EIGRP
AS 100
SanJose1SanJose2
Bandwidth =
1,657,856
=
512,000
= ,
= 512,000
The Routing Table
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Administrative Distance / MetricSanJose2#show ip route
D 192.168.72.0/24 [90/2172416]
via 192.168.64.6, 00:28:26, Serial0
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Diffusing Update Algorithm (DUAL)
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Diffusing Update Algorithm
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g p g
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The design philosophy behind DUAL isthat even temporary routing loops aredetrimental to the performance of anetwork.
DUAL Concepts
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The Diffusing Update Algorithm (DUAL) isused to prevent looping:
Successor
Feasible Distance (FD)
p
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Feasible Successor (FS)Reported Distance (RD) or Advertised
Distance (AD)
Feasible Condition or FeasibilityCondition (FC)
Successor and Feasible Distance
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SuccessorThe best least
cost route to adestinationfound in the
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rout ng ta e
Feasibledistance(FD)
The lowest
calculatedmetric along apath to adestination
network
Feasible Successor
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Feasible Successor is a loopfree backup route to samedestination as successor route
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Successors and Feasible Successors
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Successors and Feasible Successors
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Successors and Feasible Successors
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Feasibility Condition and Reported Distance
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Reported distance (RD)
The metric that a router reports to aneighbor about its own cost to that
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Feasibility Condition (FC)Met when a neighbors RD is less
than the local routers FD to thesame destination network
Successors and Feasible Successors
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172.30.1.0
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172.30.1.0
Successors and Feasible Successors
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Feasible Successor, FC: RD30 < FD31
172.30.1.0
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Advertised orDestination Feasible Dist. Reported. Dist. Neighbor
172.30.1.0 40 30 X In Topology Table
172.30.1.0 31 21 Y In Routing Table
172.30.1.0 230 220 Z Not in Topology Table(show ip eigrp topology )
Current Successor = 31RD of RTY= 21
FD to 172.30.1.0 is31 via Router Y
RTZ is NOT FeasibleSuccessor, FC:RD220 not< FD31
Successors and Feasible Successors
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Feasible Successor, FC: RD30 < FD31
172.30.1.0
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Current Successor = 31RD of RTY= 21
FD to 172.30.1.0 is31 via Router Y
RTY is successor with a computed cost of 31. 31 is the Feasible Distance (FD). RTX is a feasible successor because its RD is less than or equal to the FD.
- RTXs RD (30) is less than the FD (31).
RTZ is NOT FeasibleSuccessor, FC:RD220 not< FD31
Example of a Loop
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Cost=70Cost=19
RTZ has a Reported Distance toRTA of 220. Since its Reported
Distance is greater than RTAsown Feasibile Distance of 31,
RTA cant trust that the routeRTZ takes is somehow backthrough itself.
DUAL Concepts
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DUAL Concepts
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TheTopology table include:
1. all successor routes
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. routes
3. other routes updatedby neighbors
DUAL Concepts
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EIGRP Topology Table dissected
Active state ?
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DUAL Concepts
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No Feasible Successor
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Query and Reply Packets
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172.30.1.0X
X
QueriesQueries
RepliesReplies
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RTZ replies that it still has a route to 172.30.1.0, while RTX and RTY replythat they do not.
Current Successor is now RTZ, with a FD of 230 and a RD of RTZ= 220.
and RTX Fail!
?RTZ was previouslyNOT a FeasibleSuccessor, FC: RD220not< FD31 or FD40, but
now there is noSucessor
Finite State Machine (FSM)
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An abstract machine that defines a setof possible states something can go
through, what event causes thosestates and what events result form
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those states FSMs are used to describe how a
device, computer program, or routingalgorithm will react to a set of inputevents
Finite State Machine
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DUAL FSMSelects a best
loop-free path toa destination
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routes by usinginformation inEIGRP tables
Finite State Machine
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Finite State Machines (FSM): with Feasible Successor
To examine output from EIGRPs finite state machineus the debug eigrp fsmcommand
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Finite State Machine
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Finite State Machines (FSM): without Feasible Successor
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More EIGRP Configuration
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The Null0 Summary Route
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Automatic Summarization
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The auto-summarycommand permits EIGRPto automatically summarize at major networkboundaries
The no auto-summarycommand is used todisable automatic summarization
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updates that will not be automaticallysummarized
This will cause changes to appear in both
routing tables
topology tables
The no auto-summaryCommand
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Disabling Automatic Summarization
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More EIGRP Configurations
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Disabling Automatic Summarization: topology table change
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Manual Summarization
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Manual summarization can includesupernets
Command used to configure manualsummarization
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Router(config-if)# ip summary-addresseigrp as-number network-address subnet-mask
Manual Summarization
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Manual Summarization
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EIGRP Default Route
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Extra:EIGRP Default Route
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Gateway Router
router igrp 24
network 207.21.20.0
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ip route 0.0.0.0 0.0.0.0 207.21.20.1
ip default-network 207.21.20.0
Extra:EIGRP Default Route
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router eigrp 100
network 10.0.0.0
!
interface serial 0
ip address 10.1.1.1
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ip summary-address eigrp 100 0.0.0.0 0.0.0.0
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Fine-Tuning EIGRP
EIGRP bandwidth utilization
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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 byEIGRP is
Router(config-if)#ip bandwidth-percent eigrp as-number
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More EIGRP Configurations
Hello intervals and hold times are configurable on a per-interface basis
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Hello intervals and hold times are configurable on a per-interface basis Router(config-if)#ip hello-interval eigrp as-number seconds
Changing the hello interval also requires changing the hold time to avalue greater than or equal to the hello interval
Router(config-if)#ip hold-time eigrp as-number seconds
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EIGRP show commands
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EIGRP debug commands
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Extra:Authentication
MD5 cryptographic checksums are the only
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MD5 cryptographic checksums are the onlyauthentication supported in EIGRP, whichon first consideration might seem less
flexible than RIPv2 and OSPF, whichsupport both MD5 and clear-text passwords.
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However, clear-text password authenticationshould be used only when a neighboringdevice does not support the more secureMD5. Because EIGRP will be spoken onlybetween two Cisco devices, this situationwill never arise.
Configuring EIRGP authentication
St 1 E t fi ti d f th i t f hi h
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Step 1: Enter configuration mode for the interface on which youwant to enable authentication.
Step 2: Specify MD5 authentication for EIGRP packets using the
ip authentication mode eigrp 100 md5 command.
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Step 3: Enable the authentication of EIGRP packets with a key
Configuring EIRGP authentication
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Step 3: Enable the authentication of EIGRP packets with a keyspecified in a key chain by using the ip authentication key-chain
eigrp ASNumber key-chaincommand.
Step 4: Enter the configuration mode for the key chain using thekey chain key-chain(key-chaincan be differentin each side).
Step 5: Identify a key ID to use, and enter configuration mode fora ey us ng e ey ey- comman .
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Step 6: Identify the key string (password) for this key using the
Configuring EIRGP authentication
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Step 6: Identify the key string (password) for this key using thekey-string {key-string}command.
(key-stringmust be the sameon both side of EIGRP routers)
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Example of Authentication
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EIGRP redistribution
Planning Redistribution
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g
Locate the boundary router between two routing processes. Determine which routing process is the core or backbone
process
Determine which routing process is the edge or migration
process Select a method for injecting the required edge protocol routes
into the core.
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Configuring redistribution into EIGRP
Use this command to redistribute routes into EIGRP:
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Router(config-router)# redistribute protocol
[process-id] [match {internal | external 1 |
external 2}] [metric metric-value] [route-map map-
tag]
RtrA(config)# router eigrp 100-
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Process ID
RtrA(config-router)# redistribute ospf 1 ?
match Redistribution of OSPF routes metric Metric for redistributed routes route-map Route map reference
Default metric is infinity.
Configuring redistribution into EIGRP
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Bandwidth in kilobytes = 10000kbps.
Delay in tens of microseconds = 100ms.
Reliability = 255 (maximum).
Load = 1 (minimum).
MTU = 1,500 bytes.
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Extra:EIGRP variance command
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Let's look at an example, there are three ways to get to Network X, fromRouter E: (Note: metrics incorrectly not including outgoing interface toNet X.)
E-B-A with a metric of 30
E-C-A with a metric of 20
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router eigrp 1
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variance 2
This increases the minimum metric to 40 (2 * 20 = 40).
EIGRP includes all the routes that have a metric less than or equalto 40, and are feasible successors.
In the above configuration, EIGRP now uses two paths to get toNetwork X, E-C-A and E-B-A, because both paths have a metricunder 40.
network x.x.x.x
variance 2
Extra:EIGRP variance command
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router eigrp 1
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Two unequal-cost paths:
E-B-A with a metric of 30
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multiple routes for the same destination network that have differentcosts, use the traffic-share router configuration command.
To disable this function, use the no form of the command.
traffic-share {balanced | min}
no traffic share {balanced | min}
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balanced
Distributes traffic proportionately to the ratios of the metrics.min
Uses routes that have minimum costs
For more information:http://www.cisco.com/en/US/tech/tk365/tk207/technologies_tech_note09186a008009437d.shtml
Summary
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Describe the background and history of EIGRP
Describe the features and operation of EIGRP Examine the basic EIGRP configuration commands
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Calculate the composite metric used by EIGRP
Describe the concepts and operation of DUAL Describe the uses of additional configuration
commands in EIGRP
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