Quản trị mạng - Chapter 9: Eigrp
Describe the background and history of EIGRP
• Describe the features and operation of EIGRP
• Examine the basic EIGRP configuration commands
and identity 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
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1Chapter 9: EIGRP
CCNA Exploration version 4.0
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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.
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Introduction to EIGRP
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EIGRP
• The main purpose in Cisco's development of EIGRP was to create a classless
version of IGRP.
• EIGRP includes several features that are not commonly found in other distance
vector routing protocols like RIP (RIPv1 and RIPv2) and IGRP.
• These features include:
1. Reliable Transport Protocol (RTP)
2. Bounded Updates
3. Diffusing Update Algorithm (DUAL)
4. Establishing Adjacencies
5. 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
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
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IGRP to EIGRP
Enhanced Distance Vector Routing
Protocol: EIGRP
• Uses the Diffusing Update Algorithm
(DUAL)
• Does not age out routing entries nor
uses periodic updates.
• 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 will use a backup path if one
exists in the topology table.
• Faster convergence due to the
absence of holddown timers and a
system of coordinated route
calculations.
Traditional Distance Vector
Routing Protocols
• Use the Bellman-Ford or
Ford-Fulkerson algorithm.
• Age out routing entries and
uses periodic updates.
• Keep 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.
• Slower convergence due to
holddown timers.
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EIGRP Capabilities and Attributes
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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.
EIGRP Message Format
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• The Autonomous System (AS)
Number specifies the EIGRP
routing process.
– Unlike RIP, Cisco routers
can run multiple instances of
EIGRP.
– The AS number is used to
track multiple instances of
EIGRP.
• EIGRP Parameters contains
– Weights
– Hold time
EIGRP Message Format
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• 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 Message Format
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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 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
RTP and EIGRP Packet Types
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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 packets
–Used to propagate routing information
–Update packets are sent as a
multicast when required by multiple
routers, or as a unicast when required
by only a single router.
• Acknowledgement packets
–Used to acknowledge receipt of
update, query & reply packets
–EIGRP 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 for
networks
Query packets: can use:
Unicast
Multicast
Reply packet: use only
unicast
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• EIGRP’s use of partial bounded
updates minimizes use of bandwidth
EIGRP Bounded Updates
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Diffusing Update Algorithm (DUAL)
–Purpose:
•EIGRP’s primary method for
preventing routing loops
–Advantage:
•Provides for fast convergence
time by keeping a list of loop-
free backup routes
DUAL: An Introduction
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Administrative Distance
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• Note: Authentication does not encrypt the
router's routing table
Authentication
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Basic EIGRP Configuration
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Network Topology
• Topology used is the same as previous chapters with
the addition of an ISP router
EIGRP Network Topology
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• An autonomous system (AS) is a collection
of networks under the administrative
control of a single entity that presents a
common routing policy to the
Internet.(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
Autonomous System and Process IDs
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Autonomous System and Process IDs
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• EIGRP
autonomous
system number
actually functions
as a process ID
• Process ID
represents an
instance of the
routing protocol
running on a router
Autonomous System and Process IDs
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The router eigrp Command
• All routers in the EIGRP routing domain
must use the same process ID number
(autonomous-system number)
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• Functions of the network command
– Enables interfaces to transmit & receive EIGRP
updates
– Includes network or subnet in EIGRP updates
The network Command
Directly connected classful address
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The network Command
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 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
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 after 16 of these unicast retransmissions, the
neighbor will be declared dead.
• The time to wait for an ACK before switching from multicast to unicast is
specified by the multicast flow timer.
• Smooth Round Trip Timer (SRTT): the average elapsed time, measured in
milliseconds, between the transmission of a packet to the neighbor and the
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 IOS
software releases, any EIGRP packets received after the first hello will reset
the timer.
• The formulas for calculating the exact values of the SRTT, the RTO, and the
multicast flow timer are proprietary.
Extra: Neighbor Table
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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) Cnt Num
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
• Neighbor address: The network-layer address of the neighbor
router(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 no
EIGRP packets in the queue.
• Sequence Number: The number of last packet that is received from
that neighbor. EIGRP uses this field to acknowledge a neighbor’s
transmission and to identify packets that are out of sequence.
Extra: Neighbor Table
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• The show ip protocols command is used to verify that EIGRP is enabled
Verifying EIGRP
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Examining the Routing Table
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• By default ,
EIGRP
automatically
summarizes
routes at
major
network
boundary
Examining the Routing Table
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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 purposes
• EIGRP will automatically include a null0
summary route as child route when 2
conditions are met:
1. At least one subnet is learned via
EIGRP
2. Automatic summarization is
enabled
Introducting the Null0 Summary Route
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Examining the Routing Table
auto-summary
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EIGRP Metric Calculation
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EIGRP Metric Calculation
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• Use the show ip protocols command to verify the K
values
EIGRP Composite Metric and the K Values
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• Use the show
interfaces command
to view 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
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EIGRP Metric Calculation
Delay
• 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
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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 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
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Router(config-if)#bandwidth
kilobits
• Note – bandwidth
command does not
change the link’s
physical bandwidth
EIGRP Metric Calculation
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EIGRP Metric Calculation
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EIGRP Metric Calculation
• EIGRP uses the lowest bandwidth (BW) in its
metric calculation:
Calculated BW = (reference BW / lowest BW(kbps)*256
(reference BW = 107 )
• Delay – EIGRP uses the cumulative sum of all
outgoing interfaces:
Calculated Delay = (the sum of outgoing interface delays/10)*256
• EIGRP Metric = calculated BW + calculated
delay
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EIGRP Metric Calculation
• Calculate the metric from R2 to 192.168.1.0/24
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S0/0 192.168.64.2/30
S0/0 192.168.64.1/30
S0/1 192.168.64.6/30
S0/0 192.168.64.5/30
Fa0/0 192.168.72.1/24
Fa0/0 192.168.1.1/24
Fa0/0 192.168.1.2/24
EIGRP
AS 100
Calculated Bandwidth = (10,000,000/bandwidth kbps) * 256
Westasman
SanJose1 SanJose2
Bandwidth =
1,657,856
Bandwidth =
25,600
Delay =
512,000
Delay =
2,560
Determining the costs
FastEthernet
= (10,000,000/100,000) * 256
= 25,600
T1
= (10,000,000/1544) * 256
= 1,657,856
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S0/0 192.168.64.2/30
S0/0 192.168.64.1/30
S0/1 192.168.64.6/30
S0/0 192.168.64.5/30
Fa0/0 192.168.72.1/24
Fa0/0 192.168.1.1/24
Fa0/0 192.168.1.2/24
EIGRP
AS 100
Calculated Delay = (delay/10) * 256
Westasman
SanJose1 SanJose2
Bandwidth =
1,657,856
Bandwidth =
25,600
Delay =
512,000
Delay =
2,560
Determining the costs
FastEthernet
= (100/10) * 256
= 2,560
T1
= (20,000/10) * 256
= 512,000
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The Routing Table
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
• The design philosophy behind DUAL is
that even temporary routing loops are
detrimental to the performance of a
network.
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• The Diffusing Update Algorithm (DUAL) is
used to prevent looping:
–Successor
–Feasible Distance (FD)
–Feasible Successor (FS)
–Reported Distance (RD) or Advertised
Distance (AD)
–Feasible Condition or Feasibility
Condition (FC)
DUAL Concepts
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• Successor
– The best least
cost route to a
destination
found in the
routing table
• Feasible
distance(FD)
– The lowest
calculated
metric along a
path to a
destination
network
Successor and Feasible Distance
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• Feasible Successor is a loop
free backup route to same
destination as successor route
Feasible Successor
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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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• Reported distance (RD)
–The metric that a router reports to a
neighbor about its own cost to that
network
• Feasibility Condition (FC)
–Met when a neighbor’s RD is less
than the local router’s FD to the
same destination network
Feasibility Condition and Reported Distance
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Successors and Feasible Successors
172.30.1.0
172.30.1.0
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Successors and Feasible Successors
Advertised or
Destination 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 = 31
RD of RTY= 21
Feasible Successor, FC: RD30 < FD31
FD to 172.30.1.0 is
31 via Router Y
172.30.1.0
RTZ is NOT Feasible
Successor, FC:
RD220 not< FD31
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Successors and Feasible Successors
Current Successor = 31
RD of RTY= 21
Feasible Successor, FC: RD30 < FD31
FD to 172.30.1.0 is
31 via Router Y
172.30.1.0
• 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.
- RTX’s RD (30) is less than the FD (31).
RTZ is NOT Feasible
Successor, FC:
RD220 not< FD31
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Example of a Loop
Cost=70Cost=19
RTZ has a Reported Distance to
RTA of 220. Since its Reported
Distance is greater than RTA’s
own Feasibile Distance of 31,
RTA can’t trust that the route
RTZ takes is somehow back
through itself.
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DUAL Concepts
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DUAL Concepts
TheTopology table include:
1. all successor routes
2. all feasible successor
routes
3. other routes updated
by neighbors
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DUAL Concepts
• EIGRP Topology Table dissected
Active state ?
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DUAL Concepts
No Feasible Successor
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Query and Reply Packets
RTZ replies that it still has a route to 172.30.1.0, while RTX and RTY reply
that they do not.
Current Successor is now RTZ, with a FD of 230 and a RD of RTZ= 220.
Routes via RTY
and RTX Fail!
172.30.1.0X
?
RTZ was previously
NOT a Feasible
Successor, FC: RD220
not< FD31 or FD40, but
now there is no
Sucessor
X
Queries
Replies
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• 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
Finite State Machine (FSM)
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• DUAL FSM
– Selects a best
loop-free path to
a destination
– Selects alternate
routes by using
information in
EIGRP tables
Finite State Machine
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Finite State Machines (FSM): with Feasible Successor
• To examine output from EIGRP’s finite state machine
us the debug eigrp fsm command
Finite State Machine
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Finite State Machine
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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• 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
Automatic Summarization
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The no auto-summary Command
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Disabling Automatic Summarization
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More EIGRP Configurations
• Disabling Automatic Summarization: topology table change
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• Manual summarization can include
supernets
• Command used to configure manual
summarization
Router(config-if)# ip summary-address
eigrp as-number network-address subnet-
mask
Manual Summarization
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Manual Summarization
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Manual Summarization
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EIGRP Default Route
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Gateway Router
router igrp 24
network 207.21.20.0
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
ip summary-address eigrp 100 0.0.0.0 0.0.0.0
Extra:EIGRP Default Route
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EIGRP Default Route
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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
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More EIGRP Configurations
• 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 a
value 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
authentication supported in EIGRP, which
on first consideration might seem less
flexible than RIPv2 and OSPF, which
support both MD5 and clear-text passwords.
• However, clear-text password authentication
should be used only when a neighboring
device does not support the more secure
MD5. Because EIGRP will be spoken only
between two Cisco devices, this situation
will never arise.
Configuring EIRGP authentication
• Step 1: Enter configuration mode for the interface on which you
want 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
specified in a key chain by using the ip authentication key-chain
eigrp ASNumber key-chain command.
• Step 4: Enter the configuration mode for the key chain using the
key chain key-chain(key-chain can be different in each side).
• Step 5: Identify a key ID to use, and enter configuration mode for
that key using the key key-id command.
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Configuring EIRGP authentication
• Step 6: Identify the key string (password) for this key using the
key-string {key-string} command.
(key-string must be the same on both side of EIGRP routers)
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Configuring EIRGP authentication
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Example of Authentication
EIGRP redistribution
• Planning Redistribution
• 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:
– Router(config-router)# redistribute protocol
[process-id] [match {internal | external 1 |
external 2}] [metric metric-value] [route-map map-
tag]
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•RtrA(config)# router eigrp 100
RtrA(config-router)# redistribute ospf ?
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.
Bandwidth in kilobytes = 10000kbps.
Delay in tens of microseconds = 100ms.
Reliability = 255 (maximum).
Load = 1 (minimum).
MTU = 1,500 bytes.
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Configuring redistribution into EIGRP
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Let's look at an example, there are three ways to get to Network X, from
Router E: (Note: metrics incorrectly not including outgoing interface to
Net X.)
• E-B-A with a metric of 30
• E-C-A with a metric of 20 <<<-- Minimum Metric
• E-D-A with a metric of 45
Extra:EIGRP variance command
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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 equal
to 40, and are feasible successors.
• In the above configuration, EIGRP now uses two paths to get to
Network X, E-C-A and E-B-A, because both paths have a metric
under 40.
router eigrp 1
network x.x.x.x
variance 2
Extra:EIGRP variance command
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Two unequal-cost paths:
• E-B-A with a metric of 30 <<<-- Also below 2*20
• E-C-A with a metric of 20 <<<-- Minimum Metric
• E-D-A with a metric of 45
EIGRP doesn't use path E-D-A because it has a metric of 45, and it's not a feasible
successor. Can have up to 6 unequal cost paths.
Extra:EIGRP variance command
router eigrp 1
network x.x.x.x
variance 2
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Extra:EIGRP Traffic Share
• To control how traffic is distributed among routes when there are
multiple routes for the same destination network that have different
costs, 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}
balanced
• Distributes traffic proportionately to the ratios of the metrics.
min
• Uses routes that have minimum costs
• For more information:
9186a008009437d.shtml
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Summary
• Describe the background and history of EIGRP
• Describe the features and operation of EIGRP
• Examine the basic EIGRP configuration commands
and identity 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
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Các file đính kèm theo tài liệu này:
- ca_ex_s2m9_eigrp_1575_9184.pdf