Chapter 9 EIGRP CIS 82 Routing Protocols and Concepts Rick Graziani Cabrillo College [email protected] Last Updated: 4/28/2008

Chapter 9EIGRP

CIS 82 Routing Protocols and Concepts

Rick Graziani

Cabrillo College

[email protected]

Last Updated: 4/28/2008

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Note My web site is www.cabrillo.edu/~rgraziani. For access to these PowerPoint presentations and other

materials, please email me at [email protected].

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For further information This presentation is an

overview of what is covered in the curriculum/book.

For further explanation and details, please read the chapter/curriculum.

Book: Routing Protocols

and Concepts By Rick Graziani and

Allan Johnson ISBN: 1-58713-206-0 ISBN-13: 978-58713-

206-3

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Topics Introduction to EIGRP

EIGRP: An Enhanced Distance Vector Routing Protocol

EIGRP Message Format Protocol-Dependent Modules RTP and EIGRP Packet Types Hello Protocol EIGRP Bounded Updates DUAL: An Introduction Administrative Distance Authentication

Basic EIGRP Configuration EIGRP Network Topology Autonomous Systems and

Process IDs The router eigrp Command The network Command Verifying EIGRP Examining the Routing Table

EIGRP Metric Calculation EIGRP Composite Metric and the K

Values EIGRP Metrics Using the bandwidth Command Calculating the EIGRP Metric

DUAL DUAL Concepts Successor and Feasible Distance Feasible Successors, Feasibility

Condition, and Reported Distance Topology Table: Successor and

Feasible Successor Topology Table: No Feasible

Successor Finite State Machine

More EIGRP Configurations The Null0 Summary Route Disabling Automatic Summarization Manual Summarization EIGRP Default Route Fine-Tuning EIGRP

Introduction to EIGRP

EIGRP: An Enhanced Distance Vector Routing Protocol EIGRP Message Format Protocol-Dependent Modules RTP and EIGRP Packet Types Hello Protocol EIGRP Bounded Updates DUAL: An Introduction Administrative Distance Authentication

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Enhanced Interior Gateway Routing Protocol (EIGRP) Distance vector Classless routing protocol

Released in 1992 with Cisco IOS Software Release 9.21. Enhancement of Cisco Interior Gateway Routing Protocol (IGRP). Both are Cisco proprietary

Operate only on Cisco routers.

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The term hybrid routing protocol is sometimes used to define EIGRP. Misleading, not a hybrid between distance vector and link-state Solely a distance vector routing protocol.

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Instead of hop count, both IGRP and EIGRP use metrics composed of bandwidth, delay, reliability, and load. Only bandwidth and delay are used by default.

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EIGRP Message Format

EIGRP Header field Data field = Type/Length/Value, or TLV. Encapsulated in an IP packet.

Protocol field = 88 (EIGRP) Destination IP address = multicast 224.0.0.10.

If the EIGRP packet is encapsulated in an Ethernet frame: Destination MAC, multicast address: 01-00-5E-00-00-0A

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EIGRP Message Format

Opcode specifies the EIGRP packet type as one of the following: Update Query Reply Hello

Note: All fields are shown to provide an accurate picture of the EIGRP message format. However, only thefields relevant to the CCNA candidate are discussed.

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EIGRP Packet Header Message Format

Autonomous system number Specifies the EIGRP routing process. Unlike RIP, Cisco routers can run multiple instances of EIGRP.

(more later) EIGRP packet types are discussed later in this chapter.

Note: All fields are shown to provide an accurate picture of the EIGRP message format. However, only thefields relevant to the CCNA candidate are discussed.

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EIGRP TLV Message Format

EIGRP uses weights for its composite metric. Default, only bandwidth (K1) and delay (K3) are weighted (used)

Set to 1. Other K values are set to 0 (affect load and reliability). More later.

The hold time Amount of time the EIGRP neighbor receiving this message should wait

before considering the advertising router to be down. More later

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IP Internal Routes TLV

Metric fields: Delay and Bandwidth Reliability and Load (more later)

Subnet mask field (Prefix Length): Example, the prefix length for 255.255.255.0 is 24 (/24)

Destination field: The destination network.

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IP External Routes TLV

In this chapter, we import or redistribute a default static route into EIGRP. Additional fields All the fields used by the IP Internal TLV

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Note on MTU

Some EIGRP literature might incorrectly state that the maximum transmission unit (MTU) is one of the metrics used by EIGRP.

MTU is not a metric used by EIGRP. The MTU is included in the routing updates, but it is not used to

determine the routing metric.

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Protocol-Dependent Modules

EIGRP uses protocol-dependent modules (PDM). to route different protocols, including: IP, Internetwork Packet Exchange (IPX) AppleTalk,

PDMs are responsible for the specific routing tasks for each network layer protocol.

Example The IP-EIGRP module is responsible for: Sending and receiving EIGRP packets that are encapsulated in IP. Using DUAL to build and maintain the IP routing table.

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RTP and EIGRP Packet Types

Reliable Transport Protocol (RTP) Delivery and reception of EIGRP packets.

Cannot use the services of UDP or TCP IPX and AppleTalk do not use protocols from the TCP/IP protocol suite.

RTP includes both reliable delivery and unreliable delivery of EIGRP packets: Reliable RTP requires an acknowledgment (like TCP). Unreliable RTP does not require an acknowledgment (like UDP).

RTP can send packets either as a unicast or a multicast (224.0.0.10).

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EIGRP Packet Types – Hello Packet

Hello packets are used by EIGRP to: Discover neighbors Form adjacencies with those neighbors

EIGRP hello packets: multicasts unreliable delivery

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Update Packets Contains only the routing information needed (a change occurs) Sent only to those routers that require it. Uses reliable delivery.

Multicast when sent to multiple routers Unicast when sent to a single router

Acknowledgment (ACK) Packets Sent when reliable delivery is used (update, query, and reply

packets). Sent as an unreliable unicast.

EIGRP Packet Types – Update and Acknowledgement Packets

XEIGRP uses triggered updates

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EIGRP Packet Types – Query and Reply Packets

Used by DUAL when searching for networks and other tasks. Queries and replies use reliable delivery.

To keep this example simple, acknowledgments were omitted in the graphic.

All neighbors must send a reply regardless of whether they have a route to the downed network.

Queries can use multicast or unicast, whereas replies are always sent as unicast.

DUAL is discussed in a later section. Queries and replies packets are discussed in more detail in CCNP.

XWhy Query? Another router could be attached to the same LAN.

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Hello Protocol

Before any EIGRP packets can be exchanged between routers, EIGRP must first discover its neighbors.

EIGRP routers discover neighbors and establish adjacencies with neighbor routers using the hello packet.

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Hello Protocol

Most networks, EIGRP hello packets are sent every 5 seconds. On multipoint nonbroadcast multiaccess (NBMA) networks such as

X.25, Frame Relay, and ATM interfaces with access links of T1 (1.544 Mbps) or slower, hellos are unicast every 60 seconds.

An EIGRP router assumes that as long as it is receiving hello packets from a neighbor, the neighbor and its routes remain viable.

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Hello Protocol

Hold time - maximum time the router should wait to receive the next hello before declaring that neighbor as unreachable.

Default hold time - 3 times the hello interval, 15 seconds on most networks 180 seconds on low-speed NBMA networks

If the hold time expires: EIGRP declares the route as down DUAL searches for a new path in the topology table or by

sending out queries. More later.

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EIGRP Bounded Updates

EIGRP uses the terms partial and bounded when referring to its update packets.

EIGRP sends its updates only when the metric for a route changes. The term partial means that the update only includes

information about the route changes. The term bounded refers to the propagation of partial updates

sent only to those routers that are affected by the change. This minimizes the bandwidth required to send EIGRP packets.

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DUAL: An Introduction

Diffusing Update Algorithm (DUAL) is the convergence algorithm used by EIGRP.

First proposed by E. W. Dijkstra and C. S. Scholten. The most prominent work with DUAL has been done by J. J. Garcia-Luna-

Aceves. Routing loops, even temporary ones, can be extremely detrimental to

network performance. Distance vector routing protocols such as RIP prevent routing loops with

hold-down timers and split horizon. Although EIGRP uses both of these techniques, it uses them somewhat

differently; the primary way that EIGRP prevents routing loops is with the DUAL algorithm.

J. J. Garcia-Luna-Aceves

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1. A directly connected network on R2 goes down. R2 sends an EIGRP update message to its neighbors indicating

the network is down .

2. R1 and R3 return an EIGRP acknowledgment indicating that they have received the update from R2.

X X

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3. R2 does not have an EIGRP backup route known as a feasible successor. (more later.) So, R2 sends an EIGRP query to its neighbors asking them whether they have a

route to this downed network.4. R1 and R3 return an EIGRP acknowledgment indicating that they have received the

query from R25. R1 and R3 send an EIGRP reply message in response to the query sent by R2.

In this case, the reply would state that the router does not have a route to this network.

6. R2 returns an acknowledgment indicating that it received the reply.

Note: Much more later!

XX

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Administrative Distance When compared to other

interior gateway protocols (IGP), EIGRP is the most preferred by the Cisco IOS software because it has the lowest AD.

Later in this chapter, you learn how to configure EIGRP summary routes.

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Authentication

Like other routing protocols, EIGRP can be configured for authentication. It is good practice to authenticate transmitted routing information. This practice ensures that routers will accept routing information only from

other routers that have been configured with the same password or authentication information.

When authentication is configured on a router, the router authenticates the source of each routing update packet that it receives.

However, authentication does not encrypt the router’s routing table.

Basic EIGRP Configuration

EIGRP Network Topology Autonomous Systems and Process IDs The router eigrp Command The network Command Verifying EIGRP Examining the Routing Table

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Includes the addition of the ISP router. R1 and R2 routers have subnets that are part of the 172.16.0.0/16.

Topology

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R1’s running-confighostname R1

!

interface FastEthernet0/0

ip address 172.16.1.1 255.255.255.0

!

interface Serial0/0/0

ip address 172.16.3.1 255.255.255.252

clock rate 64000

!


ip address 192.168.10.5 255.255.255.252

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!

interface Loopback1

ip address 10.1.1.1 255.255.255.252

description Simulated ISP

!


ip address 172.16.2.1 255.255.255.0

!


ip address 172.16.3.2 255.255.255.252

!


ip address 192.168.10.9 255.255.255.252

clockrate 64000

ISP router does not physically exist in our configurations. The connection between R2 and ISP is represented with a loopback

interface on Router R2.

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!


ip address 192.168.1.1 255.255.255.0

!


ip address 192.168.10.6 255.255.255.252

clockrate 64000

!


ip address 192.168.10.10 255.255.255.252

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Autonomous Systems and Process IDs 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. Described in RFC

1930. AS numbers are assigned

by IANA and its RIR. Same authority that

assigns IP address space.

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Autonomous Systems and Process IDs Who needs an autonomous

system number? ISPs Internet backbone

providers Large institutions

connecting to other entities that also have an autonomous system number.

Uses exterior gateway routing protocol BGP.

The vast majority of companies and institutions with IP networks do not need an autonomous system number because they come under the control of a larger entity such as an ISP.

BGP

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Process ID

Both EIGRP and OSPF use a process ID to represent an instance of their respective routing protocol running on the router.

Although EIGRP refers to the parameter as an “autonomous-system” number, it actually functions as a process ID.

AS parameter is between 1 and 65,535. All routers in this EIGRP routing domain must use the same process ID

number (autonomous system number).

Router(config)# router eigrp autonomous-system

Router(config)# router eigrp 1 Must be same on all routers in EIGRP routing domain

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The router eigrp Command

EIGRP is enabled on all three routers using the process ID of 1.

R1(config)# router eigrp 1

R1(config-router)#


R2(config-router)#


R3(config-router)#

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The network Command

The network command in EIGRP has the same function as in other IGP routing protocols: Any interface on this router that matches the network address in

the network command will be enabled to send and receive EIGRP updates.

This network (or subnet) will be included in EIGRP routing updates.

Router(config-router)# network network-address

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The network Command

The network-address is the classful network address for this interface. 172.16.0.0 includes both 172.16.1.0/24 and 172.16.3.0/30 subnets.

When EIGRP is configured on R2, DUAL sends a notification message to the console stating that a neighbor relationship with another EIGRP router has been established.

This new adjacency happens automatically because both R1 and R2 are using the same EIGRP 1 routing process and both routers are now sending updates on the 172.16.0.0 network.

R1(config-router)# network 172.16.0.0


%DUAL-5-NBRCHANGE: IP-EIGRP 1: Neighbor 172.16.3.1 (Serial0/0) is up: new adjacency

Adjacency

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The network Command with a Wildcard Mask

Network command – When uses classful network address: All interfaces on the router that belong to that classful network address

will be enabled for EIGRP. To include only specific interface(s), subnets, to be enabled for EIGRP:

Use the wildcard-mask option.

Router(config-router)# network network-address [wildcard-mask]

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Think of a wildcard mask as the inverse of a subnet mask. The inverse of subnet mask 255.255.255.252 is 0.0.0.3. To calculate the inverse of the subnet mask, subtract the subnet mask from

255.255.255.255. Some Cisco IOS software versions also let you just enter the subnet

mask. However, Cisco IOS software then converts the command to the

wildcard mask format, as can be verified with the show running-config

255.255.255.255

- 255.255.255.252 Subtract the subnet mask

---------------

0. 0. 0. 3 Wildcard mask

R2(config-router)# network 192.168.10.8 0.0.0.3

Or


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Or


R2# show running-config

<some output omitted>

!

router eigrp 1

network 172.16.0.0

network 192.168.10.8 0.0.0.3

auto-summary

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The passive-interface command should not be used with EIGRP. When the passive-interface command is configured, EIGRP stops sending

hello packets on that interface. Will not form an adjacency Unable to send or receive routing updates.



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Network configurations

router eigrp 1

network 172.16.0.0

network 192.168.10.4

router eigrp 1

network 172.16.0.0

network 192.168.10.8 0.0.0.3

router eigrp 1

network 192.168.1.0

network 192.168.10.0

R2

R1

R3

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Verifying EIGRP

EIGRP routers must first establish adjacencies with their neighbors before any updates can be sent or received.

show ip eigrp neighbors - view the neighbor table and verify that adjacencies with its neighbors.

If a neighbor is not listed: Check the local interfaces to make sure it is activated with the show ip

interface brief command. Try pinging the IP address of the neighbor.

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Verifying EIGRP

If the ping is successful and EIGRP still does not see the router as a neighbor, examine the following configurations: Are both routers configured with the same EIGRP process ID? Is the directly connected network included in the EIGRP network statements?

Is the passive-interface command inappropriately configured, thus preventing EIGRP hello packets on the interface?

Verifying EIGRP

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R1# show ip protocols

Routing Protocol is “eigrp 1”

Outgoing update filter list for all interfaces is not set

Incoming update filter list for all interfaces is not set

Default networks flagged in outgoing updates

Default networks accepted from incoming updates

EIGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0

EIGRP maximum hopcount 100

EIGRP maximum metric variance 1

Redistributing: eigrp 1

Automatic network summarization is in effect

Automatic address summarization:

192.168.10.0/24 for FastEthernet0/0, Serial0/0/0

Summarizing with metric 2169856

172.16.0.0/16 for Serial0/0/1

Summarizing with metric 28160

Maximum path: 4

Routing for Networks:

172.16.0.0

192.168.10.0

Routing Information Sources:

Gateway Distance Last Update

(this router) 90 00:03:29

192.168.10.6 90 00:02:09

Gateway Distance Last Update

172.16.3.2 90 00:02:12

Distance: internal 90 external 170

Some items to make note of. These will be explained later.

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Examining the Routing Table: R1

Notice that EIGRP routes are denoted in the routing table with a D, which stands for DUAL.

R1# show ip route

Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile,

D - EIGRP, EX - EIGRP external, O - OSPF,

<Output omitted>

192.168.10.0/24 is variably subnetted, 3 subnets, 2 masks

D 192.168.10.0/24 is a summary, 00:03:50, Null0

C 192.168.10.4/30 is directly connected, Serial0/0/1

D 192.168.10.8/30 [90/2681856] via 192.168.10.6,00:02:43, S0/0/1



C 172.16.1.0/24 is directly connected, FastEthernet0/0

D 172.16.2.0/24 [90/2172416] via 172.16.3.2, 00:10:47, S0/0/0


D 192.168.1.0/24 [90/2172416] via 192.168.10.6, 00:02:31, S0/0/1

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EIGRP is a classless routing protocol (includes the subnet mask in the routing update), it supports variable-length subnet masks (VLSM) and classless interdomain routing (CIDR).

R2# show ip route

<Output omitted>



D 192.168.10.4/30 [90/2681856] via 192.168.10.10,00:03:05,S0/0/1




D 172.16.1.0/24 [90/2172416] via 172.16.3.1, 00:11:11, S0/0/0



10.0.0.0/30 is subnetted, 1 subnets

C 10.1.1.0 is directly connected, Loopback1

D 192.168.1.0/24 [90/2172416] via 192.168.10.10, 00:02:54, S0/0/1

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By default, EIGRP automatically summarizes routes at the major network boundary.

You can disable the automatic summarization with the no auto-summary command, just as you can for RIPv2.

Null0 summary routes will be explained next.

R3# show ip route

<Output omitted>





D 172.16.0.0/16 [90/2172416] via 192.168.10.5, 00:03:23, S0/0/0

[90/2172416] via 192.168.10.9, 00:03:23, S0/0/1


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Introducing the Null0 Summary Route

The 192.168.10.0/24 and 172.16.0.0/16 routes do not actually represent a path to reach the parent networks.

If a packet does not match one of the level 2 child routes, it is sent to the Null0 interface.

In other words, if the packet matches the level 1 parent, but none of the subnets, the packet is discarded.

R2# show ip route

<Output omitted>



D 192.168.10.4/30 [90/2681856] via 192.168.10.10,00:03:05,S0/0/1




D 172.16.1.0/24 [90/2172416] via 172.16.3.1, 00:11:11, S0/0/0





D 192.168.1.0/24 [90/2172416] via 192.168.10.10, 00:02:54, S0/0/1

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Introducing the Null0 Summary Route

EIGRP automatically includes a Null0 summary route as a child route whenever both of the following conditions exist: There is at least one subnet that was learned via EIGRP. Automatic summarization is enabled.

The Null0 summary route is removed when automatic summary is disabled (later).

R2# show ip route

<Output omitted>



D 192.168.10.4/30 [90/2681856] via 192.168.10.10,00:03:05,S0/0/1




D 172.16.1.0/24 [90/2172416] via 172.16.3.1, 00:11:11, S0/0/0





D 192.168.1.0/24 [90/2172416] via 192.168.10.10, 00:02:54, S0/0/1

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R3 Routing Table

Both R1 and R2 are automatically summarizing the 172.16.0.0/16 network and sending it as a single routing update.

R1 and R2 are not propagating the individual subnets because of automatic summarization.

We will turn off automatic summarization later.

R3# show ip route

<Output omitted>





D 172.16.0.0/16 [90/2172416] via 192.168.10.5, 00:03:23, S0/0/0

[90/2172416] via 192.168.10.9, 00:03:23, S0/0/1


EIGRP Metric Calculation

EIGRP Composite Metric and the K Values EIGRP Metrics Using the bandwidth Command Calculating the EIGRP Metric

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EIGRP Composite Metric and the K Values

EIGRP uses the following values in its composite metric to calculate the preferred path to a network: Bandwidth Delay Reliability Load

Note: Although MTU is included in the routing table updates, it is not a routing metric used by EIGRP or IGRP.

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The Composite Metric

By default, K1 and K3 are set to 1, and K2, K4, and K5 are set to 0. The result is that only the bandwidth and delay values are used in the

computation of the default composite metric. Note:

Modifying the metric weights is beyond the scope of this course, but their relevance is important in establishing neighbors and is discussed in a later section.

The tos (type of service) value is left over from IGRP and was never implemented. (The tos value is always set to 0.)

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Verifying the K Values

The K values on R1 are set to the default. Changing these values to other than the default is not

recommended unless the network administrator has a very good reason to do so.

Cisco recommends that these values are not modified.

R1# show ip protocols

Routing Protocol is “eigrp 1”

Outgoing update filter list for all interfaces is not set

Incoming update filter list for all interfaces is not set

Default networks flagged in outgoing updates

Default networks accepted from incoming updates

EIGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0

<output omitted>

K1 K2 K3 K4 K5

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Examining the Metric Values

show interface command, lets you can examine the actual values used for bandwidth, delay, reliability, and load in the computation of the routing metric.

Default values: bandwidth delay

R1# show interface serial 0/0/0

Serial0/0/0 is up, line protocol is up

Hardware is GT96K Serial

Description: Link to R2

Internet address is 172.16.3.1/30

MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec,

reliability 255/255, txload 1/255, rxload 1/255

<output omitted>

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Bandwidth

The bandwidth metric (1544 Kbps) is a static value used by some routing protocols such as EIGRP and OSPF to calculate their routing metric. kilobits per second (Kbps). Most serial interfaces use the default bandwidth value of 1544 Kbps or

1,544,000 bps (1.544 Mbps).

The value of the bandwidth might or might not reflect the actual physical bandwidth of the interface. Modifying the bandwidth value does not change the actual bandwidth

of the link. Should reflect actual bandwidth of the link. (next).


<output omitted>



<output omitted>

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Delay

Delay is a measure of the time it takes for a packet to traverse a route. Based on the type of link, he interface Expressed in microseconds (millionths of a second). The router does not actually track how long packets are taking to reach the

destination. Like the bandwidth value, delay is a default value that can be changed by

the network administrator.


<output omitted>



<output omitted>

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Delay

100 microseconds for Fast Ethernet interfaces.

Default value is 20,000 microseconds for serial interfaces


<output omitted>



<output omitted>

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Reliability

Reliability is a measure of the probability that the link will fail or how often the link has experienced errors.

Measured dynamically with a value between 0 and 255, with 1 being a minimally reliable link and 255 being 100 percent reliable.

Reliability is calculated on a 5-minute weighted average to avoid the sudden impact of high (or low) error rates.

Reliability is expressed as a fraction of 255; the higher the value, the more reliable the link.

So, 255/255 would be 100 percent reliable, whereas a link of 234/255 would be 91.8 percent reliable.

Remember that by default EIGRP does not use reliability in its metric calculation.


<output omitted>



<output omitted>

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Load

Load reflects the amount of traffic using the link. Value between 0 and 255. Similar to reliability, load is expressed as a fraction of 255. However, in this case, a lower load value is more desirable because it

indicates less load on the link. So, 1/255 would be a minimally loaded link. 40/255 is a link at 16 percent

capacity, and 255/255 is a link that is 100 percent saturated. Load is displayed as both an outbound, or transmit, load value (txload) and

an inbound, or receive, load value (rxload). This value is calculated on a 5-minute weighted average to avoid the

sudden impact of high (or low) channel usage. Remember that by default EIGRP does not use load in its metric

calculation.


<output omitted>



<output omitted>

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Using the bandwidth Command

Most serial links, the bandwidth metric defaults to 1544 Kbps. Correct value for bandwidth is very important to the accuracy of

routing information Use the interface command bandwidth to modify the bandwidth

metric. Use the interface command no bandwidth to restore the default

value.

Router(config-if)# bandwidth kilobits

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Using the bandwidth Command

Modify the bandwidth on the appropriate serial interfaces. Be sure to modify both ends of the link.

R1(config)# inter s 0/0/0

R1(config-if)# bandwidth 64







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Verify changes

Verify the change using the show interface command.



Hardware is PowerQUICC Serial







Hardware is PowerQUICC Serial





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Calculating the EIGRP Metric

Using the default values for K1 and K3, you can simplify this calculation to:

slowest bandwidth (or minimum bandwidth)

plus cumulative sum of all the delays

------------------------------------------------

EIGRP route metric

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Calculating the EIGRP Metric

Step 1. Determine the link with the slowest bandwidth.

That bandwidth is used for the (10,000,000/bandwidth) * 256 portion of the formula.

Step 2. Determine the delay value for each outgoing interface on the way to the destination.

Step 3. Sum the delay values and divide by 10 (sum of delay/10), and then multiply by 256 (* 256).

Step 4. Add the bandwidth and sum of delay values to obtain the EIGRP metric.

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Step 1. Determine the link with the slowest bandwidth. The serial 0/0/1 interface on R2 has a bandwidth of 1024 Kbps, or

1,024,000 bps. (Slowest) The Fast Ethernet 0/0 interface on R3 has a bandwidth of 100,000 Kbps, or

100 Mbps. (10,000,000/bandwidth) * 256 = 2,499,840

Slowest bandwidth

(10,000,000/bandwidth) * 256 = 2,499,840

Bandwidth

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Step 2. Determine the delay value for each outgoing interface on the way to the destination.

The serial 0/0/1 interface on R2 has a delay of 20,000 microseconds. The Fast Ethernet 0/0 interface on R3 has a delay of 100

microseconds.

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Step 3. Sum the delay values and divide by 10 (sum of delay/10), and then multiply by 256 (* 256).

20,000/10 + 100/10 = 2,010 Then multiplied by 256, 2,010 * 256 = 514,560 The delay portion of the composite metric is 514,560.

(20,000/10 + 100/10)256 = 514,560

Delay

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Step 4. Add the bandwidth and sum of delay values to obtain the EIGRP metric. Simply add the two values together, 2,499,840 + 514,560, to obtain the EIGRP

metric of 3,014,400.

Slowest bandwidth

2,499,840 + 514,560 = 3,014,400

Route Metric

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Calculating the EIGRP MetricR2# show ip route

<code output omitted>

D 192.168.1.0/24 [90/3014400] via 192.168.10.10, 00:00:15, S0/0/1

End of Part 1

Part 2 will be updated next week

DUAL

DUAL Concepts Successor and Feasible Distance Feasible Successors, Feasibility Condition, and Reported Distance Topology Table: Successor and Feasible Successor Topology Table: No Feasible Successor Finite State Machine

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DUAL Concepts Diffusing Update Algorithm is the algorithm used by

EIGRP. Determines:

best loop-free path loop-free backup paths (which can be used immediately)

DUAL also provides the following: Fast convergence Minimum bandwidth usage with bounded updates

DUAL uses several terms that are discussed in more detail throughout this section: Successor Feasible distance Feasible successor Reported distance or advertised distance Feasible condition or feasibility condition

78

Successor and Feasible Distance

A successor is a neighboring router that is used for packet forwarding and is the least-cost route to the destination network.

The IP address of a successor is shown in a routing table entry right after the word via.

R2# show ip route


D 192.168.1.0/24 [90/3014400] via 192.168.10.10, 00:00:15, S0/0/1

IP address of the successor

79

Successor and Feasible Distance

Feasible distance (FD) is the lowest calculated metric to reach the destination network.

FD is the metric listed in the routing table entry as the second number inside the brackets.

As with other routing protocols, this is also known as the metric for the route.

R2# show ip route


D 192.168.1.0/24 [90/3014400] via 192.168.10.10, 00:00:15, S0/0/1

Feasible Distance

80

Feasible Successors, Feasibility Condition, and Reported Distance

DUAL fast convergence because it can use backup paths to other routers known as feasible successors. Does not require to recompute DUAL.

81

Feasible Successors, Feasibility Condition, and Reported Distance

Is R1 a Feasible Successor? Does R2 know if R1 has a loop-free backup path to 192.168.1.0/24? Remember, EIGRP is a Distance Vector Routing protocol.

82

Feasible Successor

A feasible successor (FS) is a neighbor who has a loop-free backup path to the same network as the successor by satisfying the feasibility condition.

Would R2 consider R1 to be a feasible successor to network 192.168.1.0/24?

To be a feasible successor, R1 must satisfy the feasibility condition (FC).

?

83

Feasibility Condition: The FC is met when a neighbor’s reported distance (RD) to a network is less than the local router’s FD to the same destination network.

The reported distance (advertised distance) - EIGRP neighbor’s FD to the same destination network.

The metric that a router reports to a neighbor about its own cost to that network.

Feasibility Condition

1. R1: My FD to 192.168.1.0/24 is 2,172,416 (my routing table).

2. R1: I will send R2 my RD to 192.168.1.0/24 of 2,172,416.

R1# show ip route

<output omitted>

D 192.168.1.0/24 [90/2172416] via 192.168.10.6, 01:12:26, Serial0/0/1

84

If R3 is the successor, can the neighbor R1 be a Feasibile Successor to this same 192.161.0/24 network? In other words, if the link between R2 and R3 fails, can R1 immediately

be used as a backup path without a recomputation of DUAL? R1 can only be an FS (Feasible Successor) if it meets the FC (Feasibility

Condition).

Feasibility ConditionR2: If my path to R3 fails can I reach 192.168.1.0/24 via R1? Does it meet the FC?

85

R1 FD to 192.168.1.0/24 is 2,172,416. R1 reports 2,172,416 to R2 as its RD (Reported Distance)

R2’s perspective: 2,172,416 is R1’s RD (Reported Distance). R1’s perspective: 2,172,416 is its FD (Feasible Distance).

Feasibility Condition

1. R1: My FD to 192.168.1.0/24 is 2,172,416 (my routing table).

2. R1: I will send R2 my RD to 192.168.1.0/24 of 2,172,416.

R1# show ip route

<output omitted>

D 192.168.1.0/24 [90/2172416] via 192.168.10.6, 01:12:26, Serial0/0/1

86

Because the RD of R1, 2,172,416, is less than R2’s own FD of 3,014,400, R1 meets the feasibility condition.

R1 is now an FS (Feasible Successor) for R2 to the 192.168.1.0/24 network.

R1# show ip route

<output omitted>

D 192.168.1.0/24 [90/2172416] via 192.168.10.6, 01:12:26, Serial0/0/1

R2# show ip route

<output omitted>

D 192.168.1.0/24 [90/3014400] via 192.168.10.10, 00:00:15, Serial0/0/1

R1’s RD is less than R2’s FD, so R1 is the FS for 192.168.1.0/24

87

Why isn’t R1 the successor if its RD is less than R2’s FD to 192.168.1.0/24? The 64 Kbps link would be used as the “slowest bandwidth part of the metric

calculation. The total cost for R2, its FD to reach 192.168.1.0/24 is greater through R1

41,026.560 than it is through R3 3,014,400.

R1# show ip route

<output omitted>

D 192.168.1.0/24 [90/2172416] via 192.168.10.6, 01:12:26, Serial0/0/1

R2# show ip route

<output omitted>

D 192.168.1.0/24 [90/3014400] via 192.168.10.10, 00:00:15, Serial0/0/1

If R1 was the successor, the 64 Kbps link is the slowest bandwidth, plus another delay of R1’s s0/0/1. This would be a higher metric (41,026.560) than 3,014,400 via successor R3.

88

Topology Table: Successor and Feasible Successor

The successor, FD, and any FSs with their RDs are kept by a router in its EIGRP topology table or topology database.

R2# show ip eigrp topology

IP-EIGRP Topology Table for AS(1)/ID(10.1.1.1)

Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,

r - reply Status, s - sia Status

<output omitted>

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


via Connected, Serial0/1

<output omitted>

Feasible Successor

Successor

89

Topology Table: Successor and Feasible Successor

P: This route is in the passive state. DUAL is not performing its diffusing computations to determine a path for a

network The route is in a stable mode All routes should be in this state for stable routing domain. active state - DUAL is recalculating or searching for a new path,

192.168.1.0/24: This is the destination network that is also found in the routing table.

1 successors: This shows the number of successors for this network. If there are multiple equal-cost paths to this network, there will be multiple

successors. FD is 3014400: This is the FD, the EIGRP metric to reach the destination network.

90

via 192.168.10.10: This is the next-hop address of the successor, R3. This address is shown in the routing table.

3,014,400: This is the FD to 192.168.1.0/24. It is the metric shown in the routing table.

28,160: This is the RD of the successor R3’s cost to reach this network.

Serial0/0/1: This is the outbound interface used to reach this network. Also shown in the routing table.

Successor Information

91

via 172.16.3.1: This is the next-hop address of the FS, R1. 41,026,560: This would be R2’s new FD to 192.168.1.0/24 if R1 became the

new successor. 2,172,416: This is the RD of the FS or R1’s metric to reach this network.

This value, RD, must be less than the current FD of 3,014,400 to meet the FC.

■ Serial0/0/0: This is the outbound interface used to reach the FC, if this router becomes the successor.

Feasible Successor Information

92

Show eigrp topology [network]R2# show ip eigrp topology 192.168.1.0

IP-EIGRP topology entry for 192.168.1.0/24

State is Passive, Query origin flag is 1, 1 Successor(s), FD is 3014400

Routing Descriptor Blocks:

192.168.10.10 (Serial0/0/1), from 192.168.10.10, Send flag is 0x0

Composite metric is (3014400/28160), Route is Internal

Vector metric:

Minimum bandwidth is 1024 Kbit

Total delay is 20100 microseconds

Reliability is 255/255

Load is 1/255

Minimum MTU is 1500

Hop count is 1

172.16.3.1 (Serial0/0/0), from 172.16.3.1, Send flag is 0x0

Composite metric is (41026560/2172416), Route is Internal

Vector metric:

Minimum bandwidth is 64 Kbit

Total delay is 40100 microseconds

Reliability is 255/255

Load is 1/255

Minimum MTU is 1500

Hop count is 2

Successor

Feasible Successor

Default metrics calculations

Optional metrics

Other information passed in routing update (not part of composite metric)

Reported Distance of R1 to R2 for 192.168.1.0

Feasible Distance for to 192.168.1.0 if R3 was the successor. This is the metric that would be if R2’s routing table if R3 was the successor.

93

Topology Table: No Feasible Successor

Route to 192.168.1.0/24: Successor is R3 via 192.168.10.6 FD of 2,172,416

R1# show ip route




D 192.168.10.8/30 [90/3523840] via 192.168.10.6, 00:44:56, S0/0/1




D 172.16.2.0/24 [90/40514560] via 172.16.3.2, 00:45:09, S0/0/0


D 192.168.1.0/24 [90/2172416] via 192.168.10.6, 00:44:55, S0/0/1

94


Is R2 a Feasible Successor? If current path to 192.168.1.0/24 fails will R1 (DUAL) automatically use R2 as

a backup route? Is the path to 192.168.1.0/24 via R2 a guaranteed loop-free path? (more later) Does R2 meet the Feasibility Condition?

R1# show ip route

D 192.168.1.0/24 [90/2172416] via 192.168.10.6, 00:44:55, S0/0/1

?

95


The topology table only shows the successor 192.168.10.6. No Feasible Successors.

R2 is not an FS because it does not meet the FC. Topology shows that R2 has a backup route

EIGRP does not have a map of the network topology. EIGRP is a distance vector routing protocol


<output omitted>


via 192.168.10.6 (2172416/28160), Serial0/0/1

<output omitted>

96


You can view all possible links whether they satisfy the feasible condition or not by adding the [all-links] option. Even those routes that are not FSs.

Is R2 a Feasible Successor? Does R2 meet the Feasibility Condition? Is R2’s RD less than R1’s FD?

R1# show ip eigrp topology all-links

<output omitted>

P 192.168.1.0/24, 1 successors, FD is 2172416, serno 5

via 192.168.10.6 (2172416/28160), Serial0/0/1

via 172.16.3.2 (41026560/3014400), Serial0/0/0

<output omitted>Feasible Successor? (No)

Successor

R1’s FD

R2’s RD

97


Even though R2 looks like a viable backup path to 192.168.1.0/24, R1 has no idea that its path is not a potential loop back through itself.

?


<output omitted>


via 192.168.10.6 (2172416/28160), Serial0/0/1

via 172.16.3.2 (41026560/3014400), Serial0/0/0

<output omitted>

R2’s FD is 3,014,400

R2’s RD to R1 is 3,014,400

R1’s current FD is 2,172,416

R2 does not meet FC! 3,014,400 > 2,172,416

R1’s FD

R2’s RD

98


Does this mean R2 cannot be used if the successor fails? R3 can be used, but there will be a longer delay before adding it

to the routing table. Before this can happen, DUAL will need to do some further

processing, which is explained in the next topic.

?


<output omitted>


via 192.168.10.6 (2172416/28160), Serial0/0/1

via 172.16.3.2 (41026560/3014400), Serial0/0/0

<output omitted>

R2’s FD is 3,014,400

R2’s RD to R1 is 3,014,400


R2 does not meet FC! 3,014,400 > 2,172,416

99

The centerpiece of EIGRP is DUAL (EIGRP route-calculation engine). DUAL Finite State Machine (FSM)

This FSM contains all the logic used to calculate and compare routes in an EIGRP network.

Finite State Machine

100

DUAL FSM

FSMs defines: The set of possible states that something can go through What events cause those states What events result from those states

Beyond the scope of this course.

101

HUNGRY(START)

FOOD ISINEDIBLE

GET FOOD

FULL

EAT ENOUGHFOOD

NOT ENOUGHFOOD

NO FOODFOR 5

HOURS

EAT MOREFOOD EATING

FSM Example

102

DUAL FSM

R2 is currently using R3 as the successor to 192.168.1.0/24. R2 currently lists R1 as an FS


<partial output>


via 192.168.10.10 (3014400/28160), Serial0/0/1

via 172.16.3.1 (41026560/2172416), Serial0/0/0SuccessorFeasible Successor

103

DUAL FSM

shutdown command simulates a failure of the link between R2 and R3.

R2# debug eigrp fsm

R2# conf t

R2(config)# int s0/0/1

R2(config-if)# shutdown

<some debug output omitted>

DUAL: Find FS for dest 192.168.1.0/24. FD is 3014400, RD is 3014400

DUAL: 192.168.10.10 metric 4294967295/4294967295

DUAL: 172.16.3.1 metric 41026560/2172416 found Dmin is 41026560

DUAL: Removing dest 192.168.1.0/24, nexthop 192.168.10.10

DUAL: RT installed 192.168.1.0/24 via 172.16.3.1

X

104

DUAL FSM

DUAL FSM searches for and finds an FS for the route in the EIGRP topology table. The FS, R1, now becomes the successor and is installed in the routing table as the new

best path to 192.168.1.0/24.

R2# debug eigrp fsm

R2# conf t





DUAL: 192.168.10.10 metric 4294967295/4294967295

DUAL: 172.16.3.1 metric 41026560/2172416 found Dmin is 41026560



X

105

DUAL FSM

R1 now becomes the successor This route is installed in the routing table as the new best path to 192.168.1.0/24. There are no new feasible successors.

R2# show ip route


D 192.168.1.0/24 [90/41026560] via 172.16.3.1, 00:08:58, Serial0/0

X


<partial output>


via 172.16.3.1 (41026560/2172416), Serial0/0

Previous topology table

Successor

106

No Feasible Successor

What if the path to the successor fails and there are no FSs? R1 to 192.168.1.0/24

R3 is the Successor No Feasible Successors

R2 is not a FS – does not meet FC. Means that DUAL does not have a guaranteed loop-free backup

path to the network, so it wasn’t added to the topology table as an FS.

? R2’s FD is 3,014,400

R2’s RD to R1 is 3,014,400


107


Simulate a failure of the link between R1 and R3 with a shutdown on R1’s S0/0/1 interface.

? R2’s FD is 3,014,400

R2’s RD to R1 is 3,014,400



<output omitted>


via 192.168.10.6 (2172416/28160), Serial0/0/1

<output omitted>

X

108


192.168.1.0/24 network put into the active state and shows that EIGRP queries are sent to other neighbors.

R2 replies with a path to this network, This becomes the new successor Installed into the routing table.

R1# debug eigrp fsm

R1# conf t





DUAL: 192.168.10.6 metric 4294967295/4294967295

DUAL: 172.16.3.2 metric 41026560/3014400 not found Dmin is 41026560

DUAL: Dest 192.168.1.0/24 entering active state.

DUAL: rcvreply: 192.168.1.0/24 via 172.16.3.2 metric 41026560/3014400

DUAL: Find FS for dest 192.168.1.0/24. FD is 4294967295, RD is 4294967295 found



109


1. When the successor is no longer available and there is no FS, DUAL puts the route into active state.

2-3. DUAL will send EIGRP queries asking other routers for a path to this network.

3-4. Other routers return EIGRP replies, letting the sender of the EIGRP query know whether they have a path to the requested network. If none of the EIGRP replies have a path to this network, the sender of the

query will not have a route to this network.

5. If the sender of the EIGRP queries receives EIGRP replies that include a path to the requested network, the preferred path is added as the new successor and added to the routing table.

X2. Query from R1 for 192.168.1.0/24

3. Query from R2 for 192.168.1.0/24

5. Reply from R2 – Yes I have a route to 192.168.1.0/24 4. Reply from R3 – Yes I have

a route to 192.168.1.0/24

1. R1 puts 192.168.1.0/24 into Active State.

5. R1 puts route to 192.168.1.0/24 via R2 into Routing Table.

R1# show ip route


D 192.168.1.0/24 [90/41026560] via 172.16.3.2, 00:00:17, Serial0/0/0

110


This process takes longer than if DUAL had an FS in its topology table and was able to quickly add the new route to the routing table.

Note: DUAL FSM and the process of queries and replies is beyond the scope of this course.

X2. Query from R1 for 192.168.1.0/24

3. Query from R2 for 192.168.1.0/24

5. Reply from R2 – Yes I have a route to 192.168.1.0/24 4. Reply from R3 – Yes I have

a route to 192.168.1.0/24

1. R1 puts 192.168.1.0/24 into Active State.

5. R1 puts route to 192.168.1.0/24 via R2 into Routing Table.

R1# show ip route


D 192.168.1.0/24 [90/41026560] via 172.16.3.2, 00:00:17, Serial0/0/0

111


The topology table for R1 now shows R2 as the successor and shows that there are no new feasible successors.


<parital output>


via 172.16.3.2 (41026560/3014400), Serial0/0/0

X

Successor

More EIGRP Configurations

The Null0 Summary Route Disabling Automatic Summarization Manual Summarization EIGRP Default Route Fine-Tuning EIGRP

113

The Null0 Summary Route

EIGRP automatically includes a Null0 summary route as a child route whenever both of the following conditions exist: There is at least one subnet that was learned via EIGRP. Automatic summarization is enabled. (By default with EIGRP)

R1 will discard any packets that match the parent 172.16.0.0/16 classful network but do not match one of the child routes 172.16.1.0/24, 172.16.2.0/24, or 172.16.3.0/24.

For example, a packet to 172.16.4.10 would be discarded.

R1# show ip route




D 192.168.10.8/30 [90/3523840] via 192.168.10.6, 00:44:56, S0/0/1




D 172.16.2.0/24 [90/40514560] via 172.16.3.2, 00:45:09, S0/0/0


D 192.168.1.0/24 [90/2172416] via 192.168.10.6, 00:44:55, Serial0/0/1

114

The Null0 Summary Route

This Null0 summary route is a child route that will match any possible packets of the parent route that do not match another child route.

This is regardless of ip classless or no ip classless command.

Therefore denying the use of any supernet or default route.

R1# show ip route




D 192.168.10.8/30 [90/3523840] via 192.168.10.6, 00:44:56, S0/0/1




D 172.16.2.0/24 [90/40514560] via 172.16.3.2, 00:45:09, S0/0/0


D 192.168.1.0/24 [90/2172416] via 192.168.10.6, 00:44:55, Serial0/0/1

115

Disabling Automatic Summarization

Like RIP, EIGRP automatically summarizes at major network boundaries using the default auto-summary command.

R3# show ip route





D 172.16.0.0/16 [90/2172416] via 192.168.10.5, 01:08:30, Serial0/0/0


172.16.0.0/16

116


Both R1 and R2 automatically summarized those subnets to the 172.16.0.0/16 classful boundary when sending EIGRP update packets to R3.

The result is that R3 has one route to 172.16.0.0/16 through R1. R1 is the successor because of the difference in bandwidth.

R3# show ip route





D 172.16.0.0/16 [90/2172416] via 192.168.10.5, 01:08:30, Serial0/0/0


172.16.0.0/16

172.16.0.0/16

117


You can quickly see that this route is not optimal. R3 will route all packets destined for 172.16.2.0 through R1.

Across a very slow link to R2 (64 Kbps). Need R1 and R2 to send individual routes for each of the

172.16.0.0/16 subnets. In other words, R1 and R2 must stop automatically summarizing

172.16.0.0/16.

R3# show ip route

<output omitted>

D 172.16.0.0/16 [90/2172416] via 192.168.10.5, 01:08:30, Serial0/0/0

172.16.0.0/16

118


Automatic summarization can be disabled with the no auto-summary. The router configuration command eigrp log-neighborchanges is on by

default on some IOS implementations. If on, you will see output similar to that shown for R1.


R1(config-router)# no auto-summary

%DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 172.16.3.2 (Serial0/0/0) is resync: summary configured

%DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 172.16.3.2 (Serial0/0/0) is down: peer restarted

%DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 172.16.3.2 (Serial0/0/0) is up: new adjacency

<output omitted>





119

R1 no more Null0 summary routes:


D 172.16.0.0/16 is a summary, 00:46:10, Null0 This mean any packets for their parent networks that do not match a child

route, the routing table will check supernet and default routes. Unless no ip classess is used

R1# show ip route


C 192.168.10.4 is directly connected, Serial0/0/1

D 192.168.10.8 [90/3523840] via 192.168.10.6, 00:16:55, S0/0/1



D 172.16.2.0/24 [90/3526400] via 192.168.10.6, 00:16:53, S0/0/1


D 192.168.1.0/24 [90/2172416] via 192.168.10.6, 00:16:52, Serial0/0/1


120

R2 no more Null0 summary routes :



R2# show ip route


D 192.168.10.4 [90/3523840] via 192.168.10.10, 00:15:44, S0/0/1



D 172.16.1.0/24 [90/3526400] via 192.168.10.10, 00:15:44, S0/0/1





D 192.168.1.0/24 [90/3014400] via 192.168.10.10, 00:15:44, S0/0/1


121

Without automatic summarization, R3’s routing table now includes the three subnets: 172.16.1.0/24, 172.16.2.0/24, and 172.16.3.0/24.

Why does R3’s routing table now have two equal-cost paths to 172.16.3.0/24? Shouldn’t the best path only be through R1 with the 1544-Mbps link?

R3# show ip route





D 172.16.1.0/24 [90/2172416] via 192.168.10.5, 00:00:11, S0/0/0

D 172.16.2.0/24 [90/3014400] via 192.168.10.9, 00:00:12, S0/0/1

D 172.16.3.0/30 [90/41024000] via 192.168.10.5, 00:00:12, S0/0/0

[90/41024000] via 192.168.10.9, 00:00:12, S0/0/1



122


The slowest link is the 64-Kbps link that contains the 172.16.3.0/30 network.

The 1544-Mbps link and the 1024-Kbps link are irrelevant in the calculation as far as the bandwidth metric is concerned.

R3# show ip route

<output omitted>

D 172.16.3.0/30 [90/41024000] via 192.168.10.5, 00:00:12, S0/0/0

[90/41024000] via 192.168.10.9, 00:00:12, S0/0/1

172.16.3.0/24

172.16.3.0/24

123

Manual Summarization

EIGRP can be configured to summarize routes, whether or not automatic summarization (auto-summary) is enabled.

Modified topology.

124


Add two more networks to R3. With the appropriate network commands R3 will propagate these networks

to other routers.

R3(config)# interface loopback 2

R3(config-if)# ip address 192.168.2.1 255.255.255.0

R3(config-if)# interface loopback 3

R3(config-if)# ip address 192.168.3.1 255.255.255.0

R3(config-if)# router eigrp 1



125


R1 and R2 routing tables show these additional networks in their routing tables. Instead of sending three separate networks, R3 can summarize the

192.168.1.0/24, 192.168.2.0/24, and 192.168.3.0/24 networks as a single route.

R1# show ip route

D 192.168.1.0/24 [90/2172416] via 192.168.10.6, 02:07:38, S0/0/1

D 192.168.2.0/24 [90/2297856] via 192.168.10.6, 00:00:34, S0/0/1

D 192.168.3.0/24 [90/2297856] via 192.168.10.6, 00:00:18, S0/0/1

R2# show ip route

D 192.168.1.0/24 [90/3014400] via 192.168.10.10, 02:08:50, S0/0/1

D 192.168.2.0/24 [90/3139840] via 192.168.10.10, 00:01:46, S0/0/1

D 192.168.3.0/24 [90/3139840] via 192.168.10.10, 00:01:30, S0/0/1

Only pertinent routes shown

192.168.1.0/24, 192.168.2.0/24,

192.168.3.0/24 192.168.1.0/24, 192.168.2.0/24,

192.168.3.0/24

126

Determining the Summary EIGRP Route

1. Write out the networks that you want to summarize in binary.2. Find the matching bits.

Count the number of leftmost matching bits, which in this example is 22. This number becomes your subnet mask for the summarized route: /22

or 255.255.252.0.3. To find the network address for summarization, copy the matching 22 bits

and add all 0 bits to the end to make 32 bits.

The result is the summary network address and mask for 192.168.0.0/22

127

Configure EIGRP Manual Summarization

Because R3 has two EIGRP neighbors, the EIGRP manual summarization in configured on both Serial 0/0/0 and Serial 0/0/1.

Router(config-if)# ip summary-address eigrp as-number network-address subnet-mask

192.168.0.0/22

192.168.0.0/22

R3(config)# interface serial 0/0/0

R3(config-if)# ip summary-address eigrp 1 192.168.0.0 255.255.252.0

R3(config-if)# interface serial 0/0/1

R3(config-if)# ip summary-address eigrp 1 192.168.0.0 255.255.252.0

128

Verify EIGRP Manual Summarization

Summary routes lessen the number of total routes in routing tables, which makes the routing table lookup process more efficient.

Summary routes also require less bandwidth utilization for the routing updates because a single route can be sent rather than multiple individual routes.

192.168.0.0/22

192.168.0.0/22

R1# show ip route

<output omitted>

D 192.168.0.0/22 [90/2172416] via 192.168.10.6, 00:01:11, Serial0/0/1

R2# show ip route

<output omitted>

D 192.168.0.0/22 [90/3014400] via 192.168.10.10, 00:00:23, Serial0/0/1

129

EIGRP Default Route

Using a static route to 0.0.0.0/0 as a default route is not routing protocol dependent.

The “quad zero” static default route can be used with any currently supported routing protocols.

EIGRP requires the use of the redistribute static command to include this static default route with its EIGRP routing updates.

Default Route

R2(config)# ip route 0.0.0.0 0.0.0.0 loopback 1


R2(config-router)# redistribute static

Redistribute default static route in EIGRP updates

The ISP router in our topology does not physically exist. By using a loopback interface, we can simulate a connection to another router.

130

EIGRP Default Route Default Route

R1# show ip route

Gateway of last resort is 192.168.10.6 to network 0.0.0.0

D*EX 0.0.0.0/0 [170/3651840] via 192.168.10.6, 00:02:14, S0/0/1

R2# show ip route


S* 0.0.0.0/0 is directly connected, Loopback1

R3# show ip route


D*EX 0.0.0.0/0 [170/3139840] via 192.168.10.9, 00:01:25, S0/0/1


Only static default route shown, other output omitted.

131

EIGRP Default Route Default Route

R1# show ip route


D*EX 0.0.0.0/0 [170/3651840] via 192.168.10.6, 00:02:14, S0/0/1


Only static default route shown, other output omitted.

In the routing tables for R1 and R3, notice the routing source and AD for the new static default route.

D: This static route was learned from an EIGRP routing update. *: The route is a candidate for a default route. EX: The route is an external EIGRP route, in this case a static route outside

of the EIGRP routing domain. 170: This is the AD of an external EIGRP route.

132

EIGRP Default Route

There is another method to propagate a default route in EIGRP, using the ip default-network command.

More information on this command can be found at this site: http://www.cisco.com/en/US/tech/tk365/

technologies_tech_note09186a0080094374.shtml.

Default Route


133

Fine-Tuning EIGRP: EIGRP Bandwidth Utilization

By default, EIGRP uses only up to 50 percent of the bandwidth of an interface for EIGRP information.

This prevents the EIGRP process from overutilizing a link and not allowing enough bandwidth for the routing of normal traffic.

The ip bandwidth-percent eigrp command can be used to configure the percentage of bandwidth that may be used by EIGRP on an interface.

EIGRP updates use no more than 50% of the link’s bandwidth by default.

Router(config-if)# ip bandwidth-percent eigrp as-number percent

134

EIGRP Bandwidth Utilization

The ip bandwidth-percent eigrp command uses the amount of configured bandwidth (or the default bandwidth) when calculating the percent that EIGRP can use.

Here we are limiting EIGRP to no more than 50 percent of the link’s bandwidth. Therefore, EIGRP will never use more the 32 Kbps of the link’s bandwidth for

EIGRP packet traffic.



R1(config-if)# ip bandwidth-percent eigrp 1 50



R2(config-if)# ip bandwidth-percent eigrp 1 50

135

Configuring Hello Intervals and Hold Times

Hello intervals and hold times are configurable on a per-interface basis and do not have to match with other EIGRP routers to establish adjacencies. We will see later, OSPF’s Hello and other timers do need to match. The seconds value for both hello and holdtime intervals can range from

1 to 65,535 If you change the hello interval, make sure that you also change the hold

time to a value equal to or greater than the hello interval. Otherwise, neighbor adjacency will go down after the hold time expires and

before the next hello interval.

Router(config-if)# ip hello-interval eigrp as-number seconds

Router(config-if)# ip hold-time eigrp as-number seconds

136

Configuring Hello Intervals and Hold Times

The no form can be used on both of these commands to restore the default values.


R1(config-if)# ip hello-interval eigrp 1 60

R1(config-if)# ip hold-time eigrp 1 180


R2(config-if)# ip hello-interval eigrp 1 60

R2(config-if)# ip hold-time eigrp 1 180

137

Topics Introduction to EIGRP

EIGRP: An Enhanced Distance Vector Routing Protocol

EIGRP Message Format Protocol-Dependent Modules RTP and EIGRP Packet Types Hello Protocol EIGRP Bounded Updates DUAL: An Introduction Administrative Distance Authentication

Basic EIGRP Configuration EIGRP Network Topology Autonomous Systems and

Process IDs The router eigrp Command The network Command Verifying EIGRP Examining the Routing Table

EIGRP Metric Calculation EIGRP Composite Metric and the K

Values EIGRP Metrics Using the bandwidth Command Calculating the EIGRP Metric

DUAL DUAL Concepts Successor and Feasible Distance Feasible Successors, Feasibility

Condition, and Reported Distance Topology Table: Successor and

Feasible Successor Topology Table: No Feasible

Successor Finite State Machine

More EIGRP Configurations The Null0 Summary Route Disabling Automatic Summarization Manual Summarization EIGRP Default Route Fine-Tuning EIGRP

Chapter 9EIGRP

CIS 82 Routing Protocols and Concepts

Rick Graziani

Cabrillo College

[email protected]

Last Updated: 4/28/2008

Documents

Chapter 9 EIGRP CIS 82 Routing Protocols and Concepts Rick Graziani Cabrillo College [email protected] Last Updated: 4/28/2008