11-LC_Chapter_11 - Clark

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Oct 29, 2013 (3 years and 11 months ago)

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Version 4.0

OSPF

Routing Protocols and
Concepts


Chapter 11

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Objectives


OSPF Introductions


EIGRP Vs OSPF


OSPF Metric


OSPF Packets


DR and BDR election


Configurations


Troubleshooting

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OSPF Introductions

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OSPF
-

Introductions


Background of OSPF


Began in 1987


1989 OSPFv1 released in RFC 1131


This version was experimental & never deployed


1991 OSPFv2 released in RFC 1247


1998 OSPFv2
updated

in RFC 2328


1999 OSPFv3 published in RFC 2740


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OSPF Introduction


OSPF Algorithm


OSPF routers build &
maintain link
-
state
database containing
LSA received from other
routers


Information found in
database is utilized upon
execution of Dijkstra
SPF algorithm


SPF algorithm used to
create SPF tree


SPF tree used to
populate routing table

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EIGRP and OSPF

EIGRP

OSPF

Hello

packet

Hello packet

Update packet

Link
-
State Update (LSU)

Request packet

Link
-
State Request (LSR)

Reply packet

Link
-
State Update

(LSU)

Acknowledgement

(ACK)

Link
-
State Acknowledgement
(
LSAck
)

Database Description (DBD)

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EIGRP and OSPF

EIGRP

OSPF

Hello interval

= 5 sec (fast
conn
.)

Hello interval

= 10 sec (P2P/MA)

Hello interval

= 60 sec (slow
conn
.)

Hello interval

= 30 sec (NBMA)

Hold

time = 3x Hello interval

Dead

interval = 4x Hello interval

H
old time = 15/180

Dead

Interval = 40/120

Administrative

Distance = 5/90/170

Administrative

Distance =
110

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EIGRP and OSPF

EIGRP

OSPF

Authentication

Authentication

Encryption

Encryption

Autonomous system

(router
eigrp

1)

Area

(network 10.0.0.0

0.0.0.255 area 0)

Process ID

(router
ospf

1)

Bandwidth

(of lowest
conn
.) + Delay

Cumulative

bandwidth

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OSPF Metric


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OSPF Metric


COST of an OSPF route


Is the accumulated value from one router to the next

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OSPF
-

Packets


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OSPF
-

Packets


Purpose of Hello
Packet


Discover neighbors


Advertise guidelines


DR/BDR

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OSPF
-

Packets

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DR/BDR


OSPF defines five network types:


Point
-
to
-
point


Broadcast Multiaccess


Nonbroadcast Multiaccess (NBMA)


Point
-
to
-
multipoint


Virtual links

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DR/BDR


Extensive flooding of LSAs


For every LSA sent out there must be an acknowledgement of
receipt sent back to transmitting router


Consequence: lots of bandwidth consumed and chaotic traffic

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DR/BDR


2 challenges presented by multiaccess networks


Multiple adjacencies


Extensive LSA flooding

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DR/BDR


DR vs. BDR vs. DROther


Sending & Receiving LSA


DR others send LSAs via
multicast 224.0.0.6 to DR &
BDR


DR forward LSA via multicast
address 224.0.0.5 to all other
routers

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DR/BDR


Router booted first = DR


Set Priority (higher = better, 0 = DROther)


Router ID (IP Addresses)

Set Router ID

Highest Loop Back Address

Highest Active Link Address


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DR/BDR


When a DR is elected it remains as the DR until
one of the following occurs


The DR fails


The OSPF process on the DR fails


The multiaccess interface on the DR fails

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Which are DR’s and which are BDR for the Multiaccess
links.

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OSPF Configuration
-

Basic


Enable OSPF


Process id
-
A
locally
significant number between
1

and
65535


OSPF network command


network address


wildcard mask
-

the inverse of the subnet mask


area
-
id
-

area
-
id refers to the OSPF area


OSPF area is a
group of routers that share link state information

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OSPF Configuration


Bandwidth & Cost



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OSPF Configuration
-

Bandwidth

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OSPF Configurations
-

DR/BDR


Example:Router(config
-
if)#
ip ospf priority

{
0
-

255
}


0 means the router cannot become the DR or BDR


1 is the default priority value


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OSPF Configuration
-

DR/BDR


The OSPF router
-
id command


Introduced in IOS 12.0


Command syntax


Router(config)#router ospfprocess
-
id


Router(config
-
router)#router
-
id ip
-
address


Modifying the Router ID


Use the command

Router
#clear ip

ospf process

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OSPF Configuration
-

DR/BDR


Setting Loopback

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OSPF Configuration


Default Route




R1(config)#
ip route 0.0.0.0 0.0.0.0 Serial 0/0/0


R1(config
-
router)#
default
-
information originate

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OSPF Configuration

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Troubleshooting

Command

Description


show
ip

protocols

Displays

OSPF process ID,
router ID
, networks router is
advertising &
administrative
distance


show
ip

ospf

Displays
OSPF process ID,
router ID
, OSPF area information
& the last time SPF algorithm
calculated

show
ip

ospf

interface

Displays

hello interval and
dead
interval

show
ip

ospf

neighbors

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Troubleshooting


Show IP Route


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Troubleshooting


Show IP Protocols

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Troubleshooting


Routers must have same…

Area ID

Hello Interval

Network Type (IP/Appletalk)

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External OSPF

The cost of this route will not increment

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