Objectives
ƒ Examine the basic EIGRP configuration
commands and identify their purposes.
ƒ Calculate the composite metric used by
EIGRP.
EIGRP
ƒ Describe the concepts and operation of
DUAL.
ƒ Describe the uses of additional configuration
commands in EIGRP.
Routing Protocols and
Concepts – Chapter 9
ITE PC v4.0
Chapter 1
2
© 2007 Cisco Systems, Inc. All rights reserved.
Cisco Public
1
Routing Protocols
Enhanced IGRP (EIGRP) Characteristics
ƒ Advanced distance vector routing protocol
ƒ Classless - supports VLSM and CIDR
ƒ Cisco proprietary
ƒ Scalable, Fast network convergence
ƒ Uses composite metric based on:
ƒBandwidth
(used by default)
ƒDelay
(used by default)
ƒReliability
(optional)
ƒLoad
(optional)
ƒ Supports authentication
3
EIGRP Message Format
4
EIGRP
ƒ Reliable Transport Protocol (RTP)
Used instead of TCP.
RTP sends multicast or unicast packets,
depending on the message type
ƒ EIGRP messages are carried in unicast or multicast
IP packets.
Uses multicast address 224.0.0.10.
ƒ EIGRP packet header - contains AS number
ƒ EIGRP has 5 packet types
ƒ Type/Length/Value Field - data portion of EIGRP
message
Hello packets – to discover and establish
adjacencies with neighbour EIGRP routers
ƒ Protocol-dependent modules (PDM) provide a
capability for routing several different protocols
including IP, IPX, and AppleTalk
Update and Acknowledgement (ACK) packets.
Query and Reply packets
5
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1
Hello Protocol
EIGRP Updates
ƒ Hello packets are sent periodically to
ƒ EIGRP sends updates only when there is a
change in the route status
- Discover directly connected neighbors and
form adjacencies.
ƒ EIGRP updates are partial and bounded
- Confirm the link is still up
Partial – only the route information that has
changed is sent
ƒ Hello interval is 5 seconds (multicasts) or 60
seconds (unicast) by default
Bounded – only those devices that are
impacted by the change are notified
ƒ Hold time is three times the hello interval
ƒ EIGRP’s use of partial bounded updates, and
non-use of broadcasts, minimizes the use of
bandwidth
This is how long EIGRP will wait to receive an
Hello before considering the neighbor down
ƒ Hello and Hold time can be configured by the
administrator (fine tuning)
7
EIGRP Tables
8
EIGRP AD
ƒ Routing table
ƒ Administrative Distance (AD)
The best route to each network based on
Administrative Distance and Metric
–Defined as the trustworthiness of the source
route
ƒ Neighbor table
ƒ EIGRP default administrative distances
Details of EIGRP neighbor adjacencies
–Summary routes = 5
ƒ Topology table
–Internal routes
Details of all routes
= 90
–Imported routes = 170
All Successor routes
All Feasible Successor (backup) routes
FD, RD
9
Autonomous System
10
EIGRP Basic Configuration
R(config)# router eigrp autonomous-system
ƒ This is a collection of networks under the control of
a single authority (RFC 1930)
ƒ EIGRP autonomous system number actually
functions as a process ID
ƒ AS Numbers are assigned by IANA
ƒ A process ID represents an instance of the
routing protocol running on a router
ƒ Entities needing AS numbers:
ƒ Process ID is a 16-bit number: 1 to 65535
ƒ ISPs
ƒ Internet backbone providers
ƒ All routers in an EIGRP domain must use the
same process ID (or AS number)
ƒ Large institutions
ƒ We usually just use the number 1
ƒ Note that using 0 is an error
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2
The network statement
R(config-router)# network network-address
ƒ This statement has two functions:
- Determines which interfaces will send and
receive EIGRP hellos and updates
- Determines which networks or subnets will
be advertised to other EIGRP neighbors
R1(config)#
R2(config)#
router eigrp 1
network 172.16.0.0
network 192.168.10.0
router eigrp 1
network 172.16.0.0
network 192.168.10.0
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14
The network statement with Wildcard Mask
Verifying EIGRP
ƒ EIGRP routers must establish adjacencies with
their neighbors before any updates can be sent or
received
R(config-router)# network net-address [wildcard-mask]
ƒ This option is used when you want to configure
EIGRP to advertise specific subnets
ƒ To view neighbor table and verify that EIGRP has
established adjacencies with neighbors is
show ip eigrp neighbors
R3(config)#
R2#show ip eigrp neighbors
IP-EIGRP neighbors for process 1
H
Address
Interface
router eigrp 1
network 192.168.1.0
network 192.168.10.4 0.0.0.3
network 192.168.10.8 0.0.0.3
0
1
192.168.10.10
172.16.3.1
Ser0/0/1
Ser0/0/0
Hold Uptime
(sec)
13
00:00:53
12
00:00:25
SRTT
(ms)
40
40
RTO
500
500
Q
Cnt
0
0
R2#
15
Examining the Routing Table
ƒ show ip route command is used to verify EIGRP
ƒ EIGRP routes are denoted by the letter “D”
R2# show ip route
Gateway of last resort is not set
10.0.0.0/30 is subnetted, 1 subnets
10.1.1.0 is directly connected, Loopback1
172.16.0.0/16 is variably subnetted, 4 subnets, 3 masks
D
172.16.0.0/16 is a summary, 00:07:15, Null0
D
172.16.1.0/24 [90/40514560] via 172.16.3.1, 00:07:15, Serial0/0
C
172.16.2.0/24 is directly connected, FastEthernet0/0
C
172.16.3.0/30 is directly connected, Serial0/0/0
D 192.168.1.0/24 [90/3014400] via 192.168.10.10, 00:07:31, Serial0/1
192.168.10.0/24 is variably subnetted, 3 subnets, 2 masks
D
192.168.10.0/24 is a summary, 00:05:29, Null0
D
192.168.10.4/30 [90/3523840] via 192.168.10.10, 00:05:29, Serial0/1
C
192.168.10.8/30 is directly connected, Serial0/0/1
17
R2#
C
Seq
Num
10
14
16
The Null0 Summary Route
ƒ 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
ƒ EIGRP automatically includes a null0 summary
route as a child route whenever both of the
following conditions exist
–One or more subnets exists that was
learned via EIGRP
–Automatic summarization is enabled
ƒ With EIGRP, auto-summary is enabled by
default
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3
Disabling Automatic Summarization
Default auto-summary on all routers
ƒ The default auto-summary command permits
EIGRP to automatically summarize at major
network boundaries
router eigrp 1
network 192.168.1.0
network 192.168.10.4 0.0.0.3
network 192.168.10.8 0.0.0.3
ƒ The no auto-summary command is used to
disable automatic summarization
ƒ This causes all EIGRP neighbors to send updates
that will not be automatically summarized
R3# show ip route
Gateway of last resort is not set
ƒ This will cause changes to appear in both
D
C
-routing tables
-topology tables
19
no auto-summary on all routers
ƒ EIGRP calculates a composite metric based on
Bandwidth (minimum interface b/w on path)
Delay
R3# show ip route
D
C
C
R3#
(sum of link delays on path)
Reliability
Gateway of last resort is not set
C
20
EIGRP Metric Calculation
router eigrp 1
network 192.168.1.0
network 192.168.10.4 0.0.0.3
network 192.168.10.8 0.0.0.3
no auto-summary
D
D
D
D
D
C
C
R3#
172.16.0.0/16 [90/2172416] via 192.168.10.5, 01:09:36, Serial0/0
192.168.1.0/24 is directly connected, FastEthernet0/0
192.168.10.0/24 is variably subnetted, 3 subnets, 2 masks
192.168.10.0/24 is a summary, 01:09:35, Null0
192.168.10.4/30 is directly connected, Serial0/0/0
192.168.10.8/30 is directly connected, Serial0/0/1
172.16.0.0/16 is
172.16.0.0/16
172.16.1.0/24
172.16.2.0/24
172.16.3.0/30
variably subnetted, 4 subnets, 3 masks
[90/2172416] via 192.168.10.5, 00:00:01, Serial0/0
[90/2172416] via 192.168.10.5, 00:00:01, Serial0/0
[90/3014400] via 192.168.10.9, 00:00:01, Serial0/1
[90/41024000] via 192.168.10.9, 00:00:01, Serial0/1
[90/41024000] via 192.168.10.5, 00:00:01, Serial0/0
192.168.1.0/24 is directly connected, FastEthernet0/0
192.168.10.0/24 is variably subnetted, 3 subnets, 2 masks
192.168.10.0/24 [90/2681856] via 192.168.10.5, 00:00:01, Serial0/0
192.168.10.4/30 is directly connected, Serial0/0/0
192.168.10.8/30 is directly connected, Serial0/0/1
Load
ƒ using the formula:
metric = [K1*bandwidth +(K2*bandwidth/(256-load) )
+ K3*delay] * [K5/(reliability + K4)].
21
EIGRP Metric Calculation
22
The bandwidth statement
ƒ Bandwidth is a default static value (in kilobits)
which depends on the type of interface
ƒ The default K values are:
K1 and K3 = 1
ƒ On serial interfaces it defaults to 1544 kilobits
(this is a standard T1 line)
K2, K4 and K5 = 0
ƒ If the actual bandwidth is different, the
calculated metric will not be correct
ƒ This means that the default metric calculation
is:
ƒ The admin can configure the bandwidth value
on a serial interface with the statement:
metric = bandwidth + delay
ƒ The K values can be configured to include
Reliability and Load in the calculation if
required by the admin.
R(config-if)# bandwidth kilobits
ƒ Note that the bandwidth statement does not
change the link’s physical bandwidth
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4
int fa0/0
R2
ip address 172.16.2.1 255.255.255.0
config
int lo1
ip address 10.1.1.1 255.255.255.252
description To ISP
!
int s0/0/0
ip address 172.16.3.2 255.255.255.252
bandwidth 64
!
int s0/0/1
ip address 192.168.10.9 255.255.255.252
clock rate 1024000
bandwidth 1024
!
router eigrp 1
network 172.16.0.0
network 192.168.10.8 0.0.0.3
Diffusing Update Algorithm (DUAL)
ƒ DUAL is the algorithm used by EIGRP
ƒ Determines loop-free routes
ƒ Provides for fast convergence by keeping backup
routes, where possible
ƒ Minimum bandwidth usage with bounded updates
ƒ Design is based on a Finite State Machine
25
DUAL Concepts
26
DUAL Concepts
ƒ Successor
ƒ Reported distance (RD)
The best route to a destination. Added to the
routing table
The metric that a router reports to a neighbor
about its own cost to that network
ƒ Feasible distance (FD)
ƒ Feasibility Condition
The lowest calculated metric along a path to a
destination network
Met when a neighbor’s RD is less than the
local router’s FD to the same destination
network
ƒ Feasible Successor
This a loop free backup route to same
destination as the Successor route, i.e. a
backup route
27
28
Choosing the best route
ƒ After a router has received all updates from
directly connected neighbors, DUAL can
calculate its routes to each network
ƒ 1 - metric is calculated for each route
ƒ 2 - the route with lowest metric is designated
the successor & is offered to the routing table
ƒ 3 - feasible successor is found
–Criteria for feasible successor: it must have lower
reported distance to the destination than the installed
route’s feasible distance
ƒ R2 has routes to 192.168.1./24 via R3 and R1
ƒ R3 is the successor route. Why?
–Feasible routes are maintained in the topology table
29
ƒ Does the route via R1 qualify as a feasible successor?
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5
EIGRP Topology Table dissected
R2# show ip eigrp topology
IP-EIGRP Topology Table for AS 1
Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
r - Reply status
P 172.16.2.0/24, 1 successors, FD is 28160
via Connected, FastEthernet0/0
P 192.168.10.8/30, 1 successors, FD is 3011840
via Connected, Serial0/0/1
P 172.16.0.0/16, 1 successors, FD is 28160
via Summary (28160/0), Null0
P 192.168.10.0/24, 1 successors, FD is 3011840
via Summary (3011840/0), Null0
P 192.168.1.0/24, 1 successors, FD is 3014400
via 192.168.10.10 (3014400/28160), Serial0/0/1
via 172.16.3.1 (41026560/2172416), Serial0/0/0
P 172.16.3.0/30, 1 successors, FD is 40512000
via Connected, Serial0/0/0
P 172.16.1.0/24, 1 successors, FD is 40514560
via 172.16.3.1 (40514560/28160), Serial0/0/0
P 192.168.10.4/30, 1 successors, FD is 3523840
via 192.168.10.10 (3523840/2169856), Serial0/0/1
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Manual Summarization
No Feasible Successor?
ƒ Manual summarization can include supernets
ƒ A feasible successor may not be present
because the feasibility condition may not be met
Reason: EIGRP is a classless routing protocol
& includes subnet masks in updates
ƒ In other words, the reported distance of the
neighbor is greater than or equal to the current
feasible distance
ƒ Statement used to configure manual
summarization
R(config-if)# ip summary-address eigrp as net-addr subnet-mask
ƒ If the successor route goes down, the route will
change from Passive mode and be placed in
Active mode. A new route will have to be found
ƒ This will involve querying neighbors
ƒ This will take time
33
Configuring a summary route in EIGRP
ƒ Route
192.168.1.0 / 24
ƒ Route
192.168.2.0 /24
ƒ Route
192.168.3.0 /24
ƒ Summary
192.168.0.0 /22
34
EIGRP Default Routes
ƒ “quad zero” static default route
-Can be used with any currently supported
routing protocol
-Is usually configured on a router that is
connected to a network outside the EIGRP
domain
interface Serial0/0/0
ip address 192.168.10.6 255.255.255.252
ip summary-address eigrp 1 192.168.0.0 255.255.252.0 5
clock rate 64000
!
interface Serial0/0/1
bandwidth 1024
ip address 192.168.10.10 255.255.255.252
ip summary-address eigrp 1 192.168.0.0 255.255.252.0 5
ƒ EIGRP & the “Quad zero” static default route
–Requires the use of the redistribute static
command to disseminate default route in
EIGRP updates
35
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6
Redistribute static route from R2 to R1
Fine-Tuning EIGRP
R2# show run
ƒ EIGRP bandwidth utilization
router eigrp 1
network 172.16.0.0
network 192.168.10.8 0.0.0.3
no auto-summary
redistribute static
!
ip route 0.0.0.0 0.0.0.0 Loopback1
-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
R(config-if)# ip bandwidth-percent eigrp as percent
R1# show ip route
Gateway of last resort is 192.168.10.6 to network 0.0.0.0
192.168.10.0/30 is subnetted, 2 subnets
192.168.10.4 is directly connected, Serial0/0/1
192.168.10.8 [90/3523840] via 192.168.10.6, 00:12:05, Serial0/0/1
172.16.0.0/16 is variably subnetted, 3 subnets, 2 masks
C
172.16.1.0/24 is directly connected, FastEthernet0/0
D
172.16.2.0/24 [90/3526400] via 192.168.10.6, 00:12:05, Serial0/0/1
C
172.16.3.0/30 is directly connected, Serial0/0/0
D*EX 0.0.0.0/0 [170/3651840] via 192.168.10.6, 00:02:14, Serial0/0/1
D
192.168.0.0/22 [90/2172416] via 192.168.10.6, 00:12:05, Serial0/0/137
C
D
Configuring Hello Intervals and Hold Times
38
Lab 9.6.1: Basic EIGRP Configuration
ƒ Hello intervals and hold times are configurable on
a per-interface basis
This lab can be done on Packet Tracer 4.11 by
downloading the activity, with the following
limitations:
ƒ Changing the hello interval also requires changing
the hold time to a value greater than or equal to the
hello interval
ƒ The WAN cable between R1 and R3 is connected
the wrong way round when compared to the
Hands-on Lab. Delete and reconnect it.
R(config-if)# ip hello-interval eigrp as seconds
R(config-if)# ip hold-time eigrp as seconds
ƒ When no auto-summary is configured, the config
needs to be saved and the router reloaded before
the Null0 routes disappear from the routing table.
ƒ The statement to manually summarize routes is
accepted, but it does not appear to have any
effect.
39
ƒ Redistribute static statement is not implemented.
40
Lab 9.6.1: Basic EIGRP Configuration
41
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