Routing Protocols and Concepts – Chapter 9 doc

ƒ Roots of EIGRP: IGRP -Developed in 1985 to overcome RIPv1’s limited hop count -Distance vector routing protocol M t i d b IGRP -Metrics used by IGRP ƒ bandwidth used by default ƒ Dela

Routing Protocols and Concepts – Chapter 9

Introduction

ƒ Roots of EIGRP: IGRP

-Developed in 1985 to overcome

RIPv1’s limited hop count

-Distance vector routing protocol

M t i d b IGRP

-Metrics used by IGRP

ƒ bandwidth (used by default)

ƒ Delay (used by default)

ƒ Delay (used by default)

ƒ Reliability (not used by default)

ƒ Load Load (not used by default) (not used by default)

-Discontinued support starting with

IOS 12.2(13)T & 12.2(R1s4)S

ƒ EIGRP is a distance vector, classless routing protocol that was

released in 1992 with IOS 9 21

released in 1992 with IOS 9.21

ƒ As its name suggests, EIGRP is an enhancement of Cisco

IGRP (Interior Gateway Routing Protocol)

ƒ Both are Cisco proprietary protocols and only operate on Cisco Both are Cisco proprietary protocols and only operate on Cisco

routers.

ƒ The main purpose in Cisco's development of EIGRP was to

create a classless version of IGRP EIGRP includes several

features that are not commonly found in other distance vector

features that are not commonly found in other distance vector

routing protocols like RIP (RIPv1 and RIPv2) and IGRP These

– Neighbor and Topology Tables

Alth h EIGRP t lik li k t t ti t l it i

ƒ Although EIGRP may act like a link-state routing protocol, it is

still a distance vector routing protocol.

– Note: The term hybrid routing protocol is sometimes used to define

EIGRP However, this term is misleading because EIGRP is not a

hybrid between distance vector and link-state routing protocols - it is

hybrid between distance vector and link state routing protocols it is

– EIGRP does not send periodic

updates and route entries do not age

out

out

– Only changes in the routing

information, such as a new link or a

link becoming unavailable cause a

routing update to occur

–EIGRP routing updates are still g p

vectors of distances transmitted to

directly connected neighbors.

ƒ Path Determination

G

– EIGRP's DUAL maintains a topology

table separate from the routing table,

which includes both the best path to a

destination network and any backup

destination network and any backup

paths that DUAL has determined to be

loop-free

If a route becomes unavailable DUAL

– If a route becomes unavailable, DUAL

will search its topology table for a valid

backup path

If i t th t t i

• If one exists, that route is immediately entered into the routing table

If d t i t DUAL f

• If one does not exist, DUAL performs

a network discovery process to see if there happens to be a backup path

ƒ Convergence

–EIGRP does not use holddown

timers.

Instead loop free paths are

– Instead, loop-free paths are

achieved through a system of route

calculations (diffusing computations)

that are performed in a coordinated

that are performed in a coordinated

fashion among the routers

–The detail of how this is done is

beyond the scope of this course, but

the result is faster convergence than

traditional distance vector routing

protocols.

EIGRP Message Format

ƒ EIGRP Header

ƒ Data link frame header - contains

source and destination MAC

address

ƒ IP packet header - contains source

& destination IP address

ƒ EIGRP packet header - contains

AS number

ƒ Type/Length/Field - data portion of

EIGRP message

ƒ In the IP packet header, p ,

ƒ the protocol field is set to 88 to indicate EIGRP

ƒ the destination address is set to

the multicast 224.0.0.10

ƒ If the EIGRP packet is

encapsulated in an Ethernet frame,

ƒ

ƒ

ƒ 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 contains

ƒ EIGRP packet header contains

• EIGRP uses for its composite metric

• By default, only bandwidth and delay are weighted Both are set to 1

• The other K values are set to zero

– Hold time

neighbor receiving this message

neighbor receiving this message should wait before considering the advertising router to be down.

ƒ TLV: IP internal contains (EIGRP routes

within an autonomous system)

– Metric field (Delay and Bandwidth)

– Metric field (Delay and Bandwidth)

• Delay is calculated as the sum of delays from source to destination in units of 10

microseconds

• Bandwidth is the lowest configured bandwidth g

of any interface along the route

– Subnet mask field

• The subnet mask is specified as the prefix length or the number of network bits in the

b t k subnet mask.

• 255.255.255.0 is 24

– Destination field

• the address of the destination network t e add ess o t e dest at o et o

• Although only 24 bits are shown in this figure

• If a network address is longer than 24 bits, then the Destination field is extended for another 32 bits

ƒ TLV: IP external contains

– Fields used when external

routes are imported into

Protocol Dependent Modules (PDM)

ƒ EIGRP uses PDM to route several

different protocols i.e IP, IPX & AppleTalk

ƒ PDMs are responsible for the specific

routing task for each network layer

routing task for each network layer

protocol

– As you can see in the figure, EIGRP

uses different EIGRP packets and

maintains separate neighbor, topology,

and routing tables for each Network

• The IPX EIGRP module is responsible for exchanging routing information about IPX networks with other IPX EIGRP routers

How do people route IPX or Appletalk today

if they still get either

other IPX EIGRP routers

• Apple-Talk EIGRP is for Apple-talk IPX or Appletalk?

– EIGRP was designed as a Network layer g y

independent routing protocol; therefore, it cannot

use the services of UDP or TCP because IPX and

Appletalk do not use protocols from the TCP/IP

protocol suite

ƒ Characteristics of RTP

– Involves both reliable & unreliable delivery of

EIGRP packet

ƒReliable delivery requires acknowledgment

ƒReliable delivery requires acknowledgment from destination

ƒUnreliable delivery does not require an acknowledgement from destination

– Packets can be sent

ƒ Unicast

ƒ Multicast

Used to discover & form adjacencies with neighbors

– EIGRP hello packets are multicasts and use unreliable

delivery

– In other cases, such as a link-cost change, updates are multicast

– An acknowledgment packet is a hello

packet that has no data

•R2 has lost connectivity to the LAN attached to its FastEthernet interface

•R2 immediately sends an unicast Update

to R1 and R3 noting the downed route g

ƒ Query & Reply packets

ƒ Used by DUAL for searching for

•R2 has lost connectivity to the LAN

•R2 has lost connectivity to the LAN and it sends out queries to all

EIGRP neighbors

•All neighbors must send a reply regardless of whether or not they have a route to the downed network

(not require acknowledgment )

(a hello packet that has no data )

multicast Multicast &

unicast

unicast multicast unicast

ƒ Purpose of Hello Protocol

To discover neighbors & establish adjacencies with neighbor routers

– To discover neighbors & establish adjacencies with neighbor routers

ƒ Characteristics of hello protocol

Time interval for sending hello packet –Time interval for sending hello packet

ƒ 5 seconds - high bandwidth (greater than T1)

ƒ60 seconds - multipoint circuits T1 bandwidth or slower p

- Holdtime

ƒ This is the maximum time router should wait before declaring a neighbor down

ƒ Default holdtime

– 3 times hello interval

» 15 seconds

» 180 seconds

EIGRP Bounded Updates

ƒ EIGRP only sends update when there is a change in route status

ƒ Partial update

– A partial update includes only the route information that has changed

– the whole routing table is NOT sent

ƒ Bounded update

ƒ Bounded update

– When a route changes, only those devices that are impacted will be

notified of the change

ƒ EIGRP’s use of partial bounded updates minimizes use of

bandwidth

D iffusing U pdate Al gorithm (DUAL)

D iffusing U pdate Al gorithm (DUAL)

– Purpose

• EIGRP’s primary method for preventing routing loops

• And also hold-down timers and split horizon, too

– Advantage of using DUAL

P id f f t ti b k i li t f l

• Provides for fast convergence time by keeping a list of free backup routes

loop-–DUAL maintains a list of backup routes it has already determined

to be loop-free If the primary route in the routing table fails, the

best backup route is immediately added to the routing table

ƒ Administrative Distance (AD)

– Defined as the trustworthiness of the source route

ƒ EIGRP default administrative distances

– Summary routes = 5

– Internal routes = 90

– Imported routes = 170

A th ti ti

Authentication

ƒ EIGRP can

Encrypt routing information

– Encrypt routing information

– Authenticate routing information

ƒ It is good practice to authenticate It is good practice to authenticate

transmitted routing information

– This practice ensures that routers will only accept routing information from only accept routing information from other routers that have been

configured with the same password or authentication information.

authentication information

ƒ Note: Authentication does not encrypt

the router's routing table.

http://www.ciscopress.com/articles/article.asp?p=1171169&seqNum=3

Network Topology

ƒ Topology used is the same as

previous chapters with the addition

of an ISP router

– ISP router does not physically

exist

ƒ EIGRP will automatically

ƒ EIGRP will automatically

summarizes at classful boundaries,

similar to RIP.

Basic EIGRP Configuration

Basic EIGRP Configuration

ƒ Autonomous System (AS) & Process IDs

– This is a collection of networks under the control of a

– This is a collection of networks under the control of a

single authority (reference RFC 1930)

– AS Numbers are assigned by IANA

ÆÆ ARIN not IANA

– Entities needing AS numbers

ƒISP

ƒInternet Backbone prodiers

ƒInstitutions connecting to other institutions using

AS numbers

ƒ These ISPs and large institutions use the exterior gateway routing protocol or BGP, to propagate routing information

16-bit and 32-bit AS Numbers

Commencing 1 January 2007,

"16-bit only AS Numbers" refers to AS numbers in the range 0 - 65535 16 bit only AS Numbers refers to AS numbers in the range 0 65535

"32-bit only AS Numbers" refers to AS Numbers in the range 65,536 - 4,294,967,295

"32-bit AS Numbers" refers to AS Numbers in the range 0 - 4,294,967,295

Basic EIGRP Configuration

ƒ EIGRP autonomous system

number actually functions as a

number actually functions as a

process ID

– The vast majority of companies and institutions with IP networks and institutions with IP networks

do not need an AS number

– The ISP is responsible for the

ti f k t ithi it routing of packets within its autonomous system and between other autonomous systems

ƒ Process ID represents an instance

of the routing protocol running on

a router

ƒ Example

Router(config)#router eigrp autonomous-system

Basic EIGRP Configuration

The router eigrp command

ƒ The global command that enables eigrp is

router eigrp autonomous-system

-All routers in the EIGRP routing domain must use

number)

B i EIGRP C fi ti

Basic EIGRP Configuration

The Network Command

ƒ Functions of the network command

– Enables interfaces to transmit & receive EIGRP updates

– Includes network or subnet in EIGRP updates

ƒ Example p

– Router(config-router)#network network-address

The network-address is the classful network address for this interface

a single classful network statement is used on R1 to include both 172.16.1.0/24 and 172.16.3.0/30 subnets:

172.16.1.0/24 and 172.16.3.0/30 subnets:

Basic EIGRP Configuration

to advertise specific subnets

-Example

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

192.168.10.8 – 192.168.10.11

Basic EIGRP Configuration

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

ƒ Think of a wildcard mask as the inverse of a subnet mask

ƒ The inverse of subnet mask 255.255.255.252 is 0.0.0.3

ƒ To calculate the inverse of the subnet mask, subtract the subnet mask from 255.255.255.255:

255.255.255.255

- 255.255.255.252 -

0 0 0 3 Wildcard mask

B i EIGRP C fi ti

Basic EIGRP Configuration

Verifying EIGRP

ƒ EIGRP routers must establish adjacencies with their

neighbors before any updates can be sent or received g y p

ƒ Command used to view neighbor table and verify that

EIGRP has established adjacencies with neighbors is j g

show ip eigrp neighbors

SRTT (Smooth Round Trip Timer)

Queue Count - Should always be zero.

RTO (Retransmit Interval) - Used

by RTP to manage reliable

by RTP to manage reliable EIGRP packets

Sequence Number - Used to track updates, queries, and reply packets

ƒ The show ip protocols command is

also used to verify that EIGRP is

enabled

ƒ Remember, the process ID must be , p

the same on all routers for EIGRP to

establish neighbor adjacencies and

share routing information.

ƒ EIGRP's internal and external

administrative distances are also

displayed:

– Distance: internal 90 external 170

Basic EIGRP Configuration We will

Basic EIGRP Configuration

Examining the Routing

We will configure the bandwidth later

Table

ƒ The show ip route

command is also used to

verify EIGRP

– EIGRP routes are denoted

in a routing table by the letter

“ D ”

– EIGRP is a classless

ti t l (i l d th routing protocol (includes the

subnet mask in the routing

EIGRP Null0 Summary Route

ƒ EIGRP has automatically included a summary route to Null0

(192 168 10 0/24 and 172 16 0 0/16)

– Null0 is not a physical interface

– In the routing table summary routes are sourced from Null0

ƒ Reason: routes are used for advertisement purposes

– EIGRP will automatically include a null0 summary route as child route when

2 conditions are met

ƒ At least one subnet is learned via EIGRP

ƒ Automatic summarization is enabled

ƒ If the packet matches the level 1 parent - the classful network address - but none of the subnets, the packet is discarded.

Basic EIGRP Configuration

ƒ R3’s routing table shows that

the 172.16.0.0/16 network is

automatically summarized by y y

R1 & R3

– R1 and R2 are not

propagating the individual

propagating the individual

subnets because of automatic

summarization.

ƒ [Tony] We will configure the

bandwidth later Once the

EIGRP Metric Calculation

EIGRP Composite Metric & the K Values

ƒ EIGRP uses the following values in its composite metric

-Bandwidth, delay, reliability, and load (reliability and load are not used)

ƒ The composite metric used by EIGRP

ƒ The composite metric used by EIGRP

– formula used has values K1 ÆK5

K1 & K3 = 1 K2, K4, K5 = 0

EIGRP Metric Calculation

ƒ Use the sh ip protocols command to verify the K

values

Again, changing

these values to other

than the default is

not recommended

unless the network

unless the network

administrator has a

very good reason to

do so

EIGRP Metric Calculation

EIGRP Metrics

U th h i t f

ƒ Use the show interfaces

command to view metrics

ƒ EIGRP Metrics

– Bandwidth – EIGRP uses

a static bandwidth to

calculate metric

Most serial interfaces use

– Most serial interfaces use

a default bandwidth value of

1.544Mbos (T1)

– The value of the

bandwidth may or may

not reflect the actual

SPEED of the interface

– If actual SPEED of the

link differs from the

default bandwidth value,

then you should modify

the bandwidth value,

EIGRP Metric Calculation

EIGRP Metrics

ƒ Delay is the defined as the

measure of time it takes for a

measure of time it takes for a

packet to traverse a route

– it is a static value based on it is a static value based on link type to which interface is connected

–The delay value, much like the bandwidth value, is a default value that can be changed by the

that can be changed by the network administrator manually

EIGRP M t i C l l ti

EIGRP Metric Calculation

ƒ Reliability (not a default EIGRP metric)

– A measure of the likelihood that a link will fail or how often the link has

experienced errors

– Measure dynamically & expressed as a fraction of 255

• the higher the fraction the better the reliability

• the higher the fraction the better the reliability

– Reliability is calculated on a 5-minute weighted average to avoid the sudden

impact of high (or low) error rates

ƒ Load (not a default EIGRP metric) ( )

– A number that reflects how much traffic is using a link

– Number is determined dynamically and is expressed as a fraction of 255

ƒThe lower the fraction the less the load on the link

ƒThis value is calculated on a 5-minute weighted average to avoid the sudden

impact of high (or low) channel usage.