chapter 9 eigrp - w3.ualg.ptw3.ualg.pt/~jjose/cisco/ccna2/ccna2-ch9-eigrp.pdf · chapter 9 eigrp...

Chapter 9

EIGRP

João José

[email protected]

http://w3.ualg.pt/~jjose/cisco/

Based on:

Graziani, R. (2008) CIS 82 Routing Theory and Concepts

Cisco CCNA 2 Exploration - Routing


Introduction to EIGRP

EIGRP: An Enhanced Distance Vector Routing Protocol

Autonomous Systems

EIGRP Message Format

Protocol-Dependent Modules

RTP and EIGRP Packet Types

Hello Protocol

EIGRP Bounded Updates

DUAL: An Introduction

Administrative Distance

Authentication


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.


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.


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.

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.

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

Autonomous Systems

and Process IDs

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

Opcode specifies the EIGRP packet type as one of the following:

1- Update

3- Query

4- Reply

5- Hello

Note: All fields are shown to

provide an accurate picture

of the EIGRP message

format. However, only the

fields relevant to the CCNA

candidate are discussed.

EIGRP Packet Header Message Format

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 the

fields relevant to the CCNA

candidate are discussed.

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

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.

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

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.

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.

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).

Hello packets are used by EIGRP to:

Discover neighbors

Form adjacencies with those neighbors

EIGRP hello packets:

multicasts

Unreliable RTP delivery

EIGRP Packet TypesHello Packet

Acknowledgment (ACK) Packet

Sent back when reliable delivery is used.

Reliable delivery: Update, Query, Reply

Unreliable delivery: Hello (no acknowledgment packet)

Sent as an unreliable unicast.

XEIGRP Packet TypesAcknowledgement

Packet

Update

Query

Reply

Update

Query

Reply

Update Packets

Contains only the routing information needed (a change occurs)

Sent only to those routers that require it.

Uses reliable RTP delivery.

Multicast when sent to multiple routers

Unicast when sent to a single router

X

EIGRP uses

triggered

updates

EIGRP Packet TypesUpdate Packet

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 or not a route to the downed network.

Queries can use multicast or unicast

Replies are always sent as unicast

Queries and replies packets are discussed in more detail in CCNP.

X

Why Query? Another

router could be attached

to the same LAN.

EIGRP Packet Types Query and Reply

Packets

Acknowledgement packets omited,

to keep example simple

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.

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.

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.

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.

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

DUAL: An Introduction Example

A directly connected network on

R2 goes down.

1. R2 sends an EIGRP update

message to its neighbors indicating

the network is down.

X

X2. R1 and R3 return an EIGRP

acknowledgment indicating

that they have received the

update from R2.

DUAL: An Introduction Example

3. R2 doesn’t have an EIGRP backup route known as a feasible successor, 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 R2.

X

X

5. R1 and R3 send an EIGRP replymessage in response to the querysent by R2. In this case, the replywould state that the router does not have a route to this network.

6. R2 returns an acknowledgmentindicating that it received the reply.

Administrative Distance

When compared to other interior gateway protocols (IGP), EIGRP is

the most preferred by the Cisco IOS (it has the lowest Aministrative

Distance).

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

routes.

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.

EIGRP Metric Calculation

EIGRP Composite Metric and the K Values

EIGRP Metrics

Using the bandwidth Command

Calculating the EIGRP Metric

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.

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.)

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

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>

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>

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 (10-6 seconds).

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>

Delay

100 microseconds for Fast

Ethernet interfaces.

Default value is 20,000

microseconds for serial

interfaces


<output omitted>



<output omitted>

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>

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>

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

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







Verify changes

Verify the change using the show interface command.



Hardware is PowerQUICC Serial




<some output omitted>



Hardware is PowerQUICC Serial






Step 1. Determine the link with the slowest bandwidth

on the way to the destination.

Step 2. Divide 10,000,000 by the bandwidth, and multiply by 256.

(10,000,000/bandwidth) * 256 = compositeBandwidth

Step 3. Determine the delay value for each outgoing interface

on the way to the destination.

Step 4. Sum those delay values and divide by 10, then multiply by 256.

(∑delay/10)* 256 = compositeDelay

Step 5. Add the portions of the composite metric.

So, add compositeBandwidth and compositeDelay values

to obtain the EIGRP metric.

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.

Slowest

bandwidth

Step 2. Divide 10,000,000 by the bandwidth, and multiply by 256.

Slower bandwidth = 1024 Kbps

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

The bandwidth portion of the composite metric is 2,499,840

Slowest

bandwidth

(10,000,000/bandwidth) * 256

= 2,499,840

Bandwidth

Step 3. Determine the delay value for each outgoing interface.

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.

Step 3. Sum the delay values and divide by 10, then multiply by 256.

serial 0/0/1 R2 - 20,000, Fast Ethernet 0/0 R3 – 100

(20,000 + 100)/10*256 = 514,560 (compositeDelay) ((∑delay/10) * 256)

The delay portion of the composite metric is 514,560

(20,000/10 + 100/10)256

= 514,560

Delay

Step 4. Add portions of the composite metric:

(compositeBandwidth+compositeDelay)

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


R2# 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

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

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


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


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

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.

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.

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).

?

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.

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

Feasibility Condition

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).

R2: If my path to R3

fails can I reach

192.168.1.0/24 via R1?

Does it meet the FC?


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).

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


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

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 R141,026.560 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.

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



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.

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

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

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.

Route to 192.168.1.0/24:

Successor is R3 via 192.168.10.6

FD of 2,172,416

R1# show ip route

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

D 192.168.10.0/24 is a summary, 00:45:09, Null0

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

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



C 172.16.1.0/24 is directly connected, FastEthernet0/0

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

Topology Table:

No 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

?

Topology Table:


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>

Topology Table:


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.


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

Topology Table:


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 3,014,400R1’s current FD

is 2,172,416

R2 does not meet FC!

3,014,400 > 2,172,416

R1’s FD

R2’s RD

Topology Table:


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 2,172,416

R2 does not meet FC!

3,014,400 > 2,172,416

Topology Table:


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

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.

FSM Example

HUNGRY

(START)

FOOD IS

INEDIBLEGET FOOD

FULL

EAT ENOUGH

FOOD

NOT ENOUGH

FOOD

NO FOOD

FOR 5

HOURS

EAT MORE

FOOD EATING

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), Serial0/0/0

Successor

Feasible Successor

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

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

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

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 2,172,416

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 2,172,416


<output omitted>


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

<output omitted>

X

No Feasible

Successor


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




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.


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

No Feasible

Successor

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

Please check for

EIGRP Configuration

after the class (last slides)

This presentation is available at:


Original presentations from:

http://www.cabrillo.edu/~rgraziani/

Cisco curriculum available at:

http://cisco.netacad.net (Internet Explorer recommended)

After login, under: “Course Materials”

http://cisco.netacad.net/

EIGRP Configuration

Basic EIGRP Configuration

EIGRP Network Topology

Autonomous Systems and Process IDs

The router eigrp Command

The network Command

Verifying EIGRP

Examining the Routing Table

Topology

Includes the addition of the ISP router.

R1 and R2 routers have subnets that are part of the 172.16.0.0/16.

R1’s running-config

hostname 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


ISP router does not physically exist in our configurations.

The connection between R2 and ISP is represented with a loopback

interface on Router R2.

hostname R2

!

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


hostname R3

!


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

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.

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

Autonomous Systems

and Process IDs

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

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)#

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

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

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]

The network Command with a Wildcard Mask

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


The network Command with a Wildcard Mask


Or


R2# show running-config


!

router eigrp 1

network 172.16.0.0

network 192.168.10.8 0.0.0.3

auto-summary

The network

Command with a

Wildcard Mask

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.


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

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.

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

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.

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>




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




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


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


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


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

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

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


More EIGRP Configurations

The Null0 Summary Route

Disabling Automatic Summarization

Manual Summarization

EIGRP Default Route

Fine-Tuning EIGRP


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


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

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

Disabling

Automatic

Summarization

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

Disabling

Automatic

Summarization

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


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


down: peer restarted


up: new adjacency

<output omitted>






R1 no more Null0 summary routes:



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


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


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


Disabling

Automatic

Summarization

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

Manual Summarization

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

Modified topology.

Manual

Summarization

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



Manual

Summarization

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,

192.168.3.0/24192.168.1.0/24,

192.168.2.0/24,

192.168.3.0/24

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: /22or 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

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

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

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.

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

Redistribute

default static

route in EIGRP

updates

Only static default route shown,

other output omitted.

EIGRP Default

Route

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.

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

Redistribute

default static

route in EIGRP

updates

Only static default route shown,

other output omitted.

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_note09186a

0080094374.shtml.

Default Route

Redistribute

default static

route in EIGRP

updates

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

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

EIGRP Bandwidth

Utilization

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

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

chapter 9 eigrp - w3.ualg.ptw3.ualg.pt/~jjose/cisco/ccna2/ccna2-ch9-eigrp.pdf · chapter 9 eigrp...

Documents