Routing Protocols and Concepts – Chapter 9 doc

EIGRP
Routing Protocols and Concepts – Chapter 9
© 2007 Cisco Systems, Inc. All rights reserved. Cisco Public
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Introduction
Introduction
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EIGRP
 Roots of EIGRP: IGRP
-Developed in 1985 to overcome
RIPv1’s limited hop count
-Distance vector routing protocol
Mti db IGRP
-
M
e
t
r
i
cs use
d

b
y
IGRP
bandwidth (used by default)


Delay (used by default)

Delay

(used

by

default)
Reliability (not used by default)

Load
(not used by default)
Load

(not

used

by

default)
-Discontinued support starting with
IOS 12.2(13)T & 12.2(R1s4)S
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EIGRP

 EIGRP is a distance vector, classless routing protocol that was
released in 1992 with IOS 9 21
released

in

1992

with

IOS

9
.
21
.
 As its name suggests, EIGRP is an enhancement of Cisco
IGRP (Interior Gateway Routing Protocol).

Both are Cisco proprietary protocols and only operate on Cisco
Both

are

Cisco

proprietary

protocols

and

only

operate

on

Cisco

routers.
 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
features include:
–Reliable Transport Protocol (RTP)
–
Bounded U
p
dates
p
–Diffusing Update Algorithm (DUAL)
–Establishing Adjacencies
–Neighbor and Topology Tables
Alth h EIGRP t lik li k
tt ti t liti

Alth
oug
h

EIGRP
may ac
t

lik
e a
li
n

k
-s
t
a
t
e rou
ti
ng pro
t
oco
l
,
it

i
s
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
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hybrid

between

distance

vector

and

link
state

routing

protocols

it

is

solely a distance vector routing protocol. Therefore, Cisco is no
longer using this term to refer to EIGRP.
EIGRP

The Algorithm

The

Algorithm
–EIGRP uses the Diffusing Update
Algorithm (DUAL).

–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
li k b i il bl
li
n
k

b
ecom
i
ng unava
il
a
bl
e cause a
routing update to occur.
–
EIGRP routin
g
u
p
dates are still
gp
vectors of distances transmitted to
directly connected neighbors.

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EIGRP
 Path Determination
G
–
EI
G
RP'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 ex
i
s
t
s,
th
a
t
rou
t
e
i
s
immediately entered into the routing
table.

If d t i t DUAL f
•
If
one
d
oes no
t
ex
i
s
t
,
DUAL
per
f
orms
a network discovery process to see if
there happens to be a backup path
that did not meet the requirement of
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that

did

not

meet

the

requirement

of

the feasibility condition.
EIGRP
 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.
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EIGRP
EIGRP
EIGRP Message Format

EIGRP Header
EIGRP

Header
Data link frame header - contains
source and destination MAC

address
IP packet header - contains source
& destination IP address
EIGRP packet header - contains
AS number
AS

number
Type/Length/Field - data portion of
EIGRP message
In the IP
p
acket header
,

p,
the protocol field is set to 88 to
indicate EIGRP
the destination address is set to
th lti t2240010
th
e mu
lti
cas
t

224
.
0
.

0
.
10
.
If the EIGRP packet is
encapsulated in an Ethernet frame,

the destination MAC address is
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
the

destination

MAC

address

is

also a multicast address: 01-00-
5E-00-00-0A.
EIGRP
EIGRP
 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

EIGRP

packet

header
contains
–Opcode field
•Update
•
Query
Query
•Reply
•Hello
–Autonomous System number
S
• The A
S
number is used to track multiple
instances of EIGRP.
 EIGRP Parameters contains
–
Weights
Weights
•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
•The amount of time the EIGRP
neighbor receiving this message
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neighbor

receiving

this

message

should wait before considering the
advertising router to be down.
EIGRP
EIGRP
 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 confi
g
ured 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
bt k
su
b
ne
t
mas
k
.
•255.255.255.0 is 24
–Destination field
•
t
h
e

add

r
ess

o
f
t
h
e

dest
in
at
i
o
n n
et
w
o
rk.
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
 TLV: IP external contains
–Fields used when external
routes are imported into
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EIGRP routing process
– import or redistribute a route into EIGRP.
EIGRP
EIGRP
Protocol Dependent Modules (PDM)
EIGRP PDM t t l

EIGRP
uses
PDM

t
o rou
t
e severa
l

different protocols i.e. IP, IPX & AppleTalk
 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
iti t
ihb t l
ma
i
n
t
a
i
ns separa
t
e ne
i
g
hb
or,
t
opo
l
ogy,
and routing tables for each Network
layer protocol.
•
The IP
-

EIGRP module is responsible
The

IP
EIGRP

module

is

responsible

for sending and receiving EIGRP
packets that are encapsulated in IP
and for using DUAL to build and
maintain the IP routin
g
table.
How do people route
g
•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
IPX A l t lk?
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other

IPX

EIGRP

routers
.
•Apple-Talk EIGRP is for Apple-talk
IPX
or
A
pp
l
e
t
a
lk?
EIGRP
EIGRP
Reliable Transport Protocol (RTP)

P rpose of RTP

P
u
rpose

of

RTP
–Used by EIGRP to transmit and receive EIGRP
packets
–
EIGRP was desi
g
ned as a Network la
y
er
gy
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.
 Characteristics of RTP
–Involves both reliable & unreliable delivery of
EIGRP packet

Reliable delivery requires acknowledgment

Reliable

delivery

requires

acknowledgment

from destination
Unreliable delivery does not require an
acknowledgement from destination
Pkt b t
–
P
ac
k
e
t
s can
b
e sen
t

Unicast
Multicast
–
Using address 2240010
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–

Using

address

224
.
0
.
0
.
10
EIGRP
EIGRP
EIGRP’s 5 Packet Types
•Hello
•Update
•
ACK
 Hello packets
–
Used

to

d
i
sco
v
e
r

&
f
o
rm
adjace
n
c
i
es
wi
t
h n
e
i
g
h
bo
r
s
ACK
•Query
•Reply
Used

to

discover

&

form

adjacencies
with

neighbors
–EIGRP hello packets are multicasts and use unreliable
delivery.
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EIGRP
EIGRP
 Update packets
–
Update packets are used to propagate
•Hello
•Update
•
ACK
Update

packets

are

used

to

propagate

routing information
–Update packets are sent only when
necessary.
G
ACK
•Query
•Reply
–
EI
G
RP updates are sent only to those
routers that require it.
–When a new neighbor is discovered,
unicast u
p
date
p
ackets are sent so that the
pp
neighbor can build up its topology table.
–In other cases, such as a link-cost
change, updates are multicast.
Udt l t ittd libl
–
U
p
d

a
t
es a
l
ways are
t
ransm
itt
e
d
re
li
a
bl
y
 Acknowledgement packets
–Used to acknowledge receipt of update,
query & reply packets
–An acknowledgment packet is a hello
packet that has no data.
EIGRP acknowledgement packets are
•R2 has lost connectivity to the LAN
attached to its FastEthernet interface.
•R2 immediately sends an unicast Update
to R1 and R3 notin
g
the downed route.
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–
EIGRP

acknowledgement

packets

are

always sent as an unreliable unicast
g
•R1 and R3 respond with an unicast
acknowledgement.
EIGRP
Q&Rlkt
•Hello
•Update
•
ACK

Q
uery
&

R
ep
l
y pac
k

e
t
s
Used by DUAL for searching for
networks
ACK
•Query
•Reply
networks
Queries and replies use reliable
delivery.
Query packets can use
Multicast
Rl kt l

R
ep
l
y pac
k
e
t
use on
l
y
unicast
•
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
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regardless of whether or not they
have a route to the downed network.
EIGRP
Query Update Reply Hello
Acknowledge
Reliable Reliable Reliable Unreliable Unreliable
(not require
acknowledgment )
(a hello packet that
has no data )

multicast Multicast &
unicast
unicast multicast unicast
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EIGRP
EIGRP
 Purpose of Hello Protocol
To
discover neighbors
&
establish
adjacencies
with neighbor routers
–
To

discover

neighbors
&

establish
adjacencies
with

neighbor

routers
 Characteristics of hello protocol
Time interval for sending hello packet
–
Time

interval

for

sending

hello

packet
5 seconds - high bandwidth (greater than T1)
60 seconds - multi
p
oint circuits T1 bandwidth or slower
p
-Holdtime
This is the maximum time
router should wait before
declaring a neighbor down
Default holdtime
–3 times hello interval
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»15 seconds
»180 seconds
EIGRP
EIGRP
EIGRP Bounded Updates
 EIGRP only sends update when there is a change in route status
 Partial update
–
A partial update includes only the route information that has changed
– the whole routing table is NOT sent

Bounded update

Bounded

update
–When a route changes, only those devices that are impacted will be
notified of the change
 EIGRP’s use of partial bounded updates minimizes use of
bandwidth
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EIGRP
EIGRP
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
Pidfft ti bk i litfl
•
P
rov
id
es
f
or
f
as
t
convergence
ti
me

b
y
k
eep
i
ng a
li
s
t
o
f

l
oop-
free backup routes
–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.
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EIGRP
 Administrative Distance (AD)
–Defined as the trustworthiness of the source route
 EIGRP default administrative distances
–
Summary routes
=
5

Summary

routes

5
–Internal routes = 90
–Imported routes = 170
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EIGRP
Ath ti ti
A
u
th
en
ti
ca
ti
on
 EIGRP can
Encrypt routing information
–
Encrypt

routing

information
– Authenticate routing information


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.

 Note: Authentication does not encrypt
the router's routing table.
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/>EIGRP
EIGRP
Network Topology
 Topology used is the same as
previous chapters with the addition
of an ISP router
–ISP router does not physically
exist

EIGRP will automatically

EIGRP

will

automatically

summarizes at classful boundaries,
similar to RIP.
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Basic EIGRP Configuration
Basic

EIGRP

Configuration

 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
A
RIN not IAN
A
–Entities needing AS numbers
ISP

Internet Backbone prodiers
Internet

Backbone

prodiers
Institutions connecting to other institutions using
AS numbers
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
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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
Basic

EIGRP

Configuration
 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
rou
ti
ng o
f
pac
k
e
t
s w
ithi
n
it
s
autonomous system and between
other autonomous systems.
 Process ID represents an instance
of the routing protocol running on
a route

r
 Example
Router(config)#router eigrp autonomous-system
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Basic EIGRP Configuration
The
router eigrp
command
The

router

eigrp
command
 The global command that enables eigrp is
ti
t
t
rou
t
er e
i
grp au
t
onomous
-
sys

t
em
-All routers in the EIGRP routing domain must use
th ID b
(
th
e same process
ID
num
b
e
r
(
autonomous-system
number)
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