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LE-201 - Unicast Routing and L3 Switch Configuration
Module 4 - 1 OSPF Overview and Configuration
Module 4
OSPF Overview and
Configuration

Module Objectives
 Define OSPF, features, advantages over RIP
 Describe OSPF LSA, format and Types
 Define LSDB, Initial synchronization, database
exchange & reliable flooding
 Describe Routing Calculations, supported network
type & Database Synchronization
 Describe how to build OSPF Networks
 Define the OSPF routing, areas, router types and
virtual Links
 Differentiate DR, BDR, Router Election
 OSPF Configuration and Examples
 Lab Exercises
 Summary

Define OSPF
 Dynamic Routing Protocol
 Link State Protocol
 Employ a distributed database model
 More efficient than RIP

The OSPF Advantage
 OSPF is an interior gateway protocol (IGP)
that is more efficient than RIP.
 Consumes fewer network resources
 Highly scalable
 Faster convergence
 A more descriptive routing metric
 Route load sharing
 Greater security

 Employ a distributed database model.
 Each router advertises a description of its
local environment
 interfaces
 costs
 neighbor information
 Uses a single synchronized database for
collecting advertisements (LSDB)
 Routing table is derived from this database
 Utilize a shortest-path first algorithm
 OSPF is a Link-state routing protocol
Link-state Protocol

Basic Features of OSPF
 Hello Packets
 Link State Advertisements (LSA)
 Link State Database
 Reliable Flooding
 Shortest Path First Routing Calculations
 Areas and Inter-area Routing

OSPF Hello Packet & Neighbor Discover
 OSPF Hello packets are sent out all of a
router’s interfaces to advertise itself to
neighbor routers
 A router learns about its neighbors when it
receives neighbor router’s Hello packet
 Hello packets are sent out every 10 seconds
by default
 If subsequent Hello packet is not received
within 40 seconds, neighbor relationship is
terminated

OSPF Hello Packets
 Will only be recognized by routers attached
to the same subnet with same subnet mask
 Contains information on parameters for
 Hello Interval and
 Router Dead Interval
 This information is used by neighbor routers
to agree on the communication variables
 This allows an occasional lost Hello packet
not to be interpreted as a link down
condition.

OSPF Hello Packets (cont.)
 In a broadcast environment, it contains the
OSPF router IDs of all routers the sender has
heard up to the point of transmission
 This reduces overhead of sending multiple
Hellos
 Ensure that the OSPF link is bi-directional
 NOTE: An OSPF router will not forward data
packets over a unidirectional link.

Link State Advertisement (LSA)
 Each OSPF router is responsible for
describing its local piece of the routing
topology through the transmission of link-
state advertisements.
 Every thirty minutes a router will -- even in
the absence of any change, retransmit this
self-originating data in the event it may have
been lost or corrupted in a neighbor router’s
tables.

OSPF LSA Format
 All OSPF LSAs start
with a 20-byte
common header
 This provides orderly
updating and removal of
LSAs and organization to
the LSDB
LS Age
Link State ID
Advertising Router
LS Sequence Number
LS Checksum
Length
Options LS Type

LSA Format - LS Age
 Number of seconds since
the LSA was originated
normally 0 - 30 mins.
 If LSA reaches 30 minutes,
originating router will
refresh the LSA by flooding
a new instance.
 If LSA reaches 1 hour, it is
deleted from the database.
LS Age
Link State ID
Advertising Router
LS Sequence Number
LS Checksum
Length
Options LS Type

LSA Format - LS Type
 Classifies the LSA
according to function
 Type 1
 Type 2
 Type 3
 Type 4
 Type 5
 Type 7
LS Age
Link State ID
Advertising Router
LS Sequence Number
LS Checksum
Length
Options LS Type

LSA Format - Link State ID
 A unique identification
 Used to describe a router
in the OSPF routing
domain
 Depends on the LS Type
 Type 1, 2, 3, 4, 5 or 7
LS Age
Link State ID
Advertising Router
LS Sequence Number
LS Checksum
Length
Options LS Type

LSA Format - Advertising Router
 The originating router’s
OSPF router ID
 In practice, this is one of
the router’s IP address
LS Age
Link State ID
Advertising Router
LS Sequence Number
LS Checksum
Length
Options LS Type

LSA Format - LS Sequence Number
 A linear sequence number
 Used to compare a new
LSA with an old LSA
 The LSA instance having
the larger LS Sequence
Number is considered to
be more recent.
LS Age
Link State ID
Advertising Router
LS Sequence Number
LS Checksum
Length
Options LS Type

LSA Format - LS Checksum
 Used to detect data
corruption.
 Does not include LS
Age field
 Derived using Fletcher
checksum algorithm
LS Age
Link State ID
Advertising Router
LS Sequence Number
LS Checksum
Length
Options LS Type

LSA Types
Type Number Description
1 Router-LSAs
2 Network-LSAs
3 Summary-LSAs (IP network)
4 Summary-LSAs (ASBR)
5 AS external-LSAs
7 NSSA external-LSAs

LS Type 1 - Router-LSAs
 Generated by each OSPF
router
 It describes the router’s set
of active interfaces, its
associated cost and any
neighbor information
 Link State ID is set to the
router’s OSPF Router ID
 Flooded throughout a
single area only
LS Age
Link State ID
Advertising Router
LS Sequence Number
LS Checksum
Length
Options LS Type

LS Type 2 - Network-LSAs
 Generated by OSPF
Designated Routers (DRs)
 Describes a network
segment - i.e., broadcast
domain along with the IDs
of all currently attached
routers.
 Link State ID field lists the
IP interface address of the
DR
LS Age
Link State ID
Advertising Router
LS Sequence Number
LS Checksum
Length
Options LS Type

LS Type 3 - Summary-LSAs (IP Network)
 This originate from Area
Border Routers (ABRs)
 Supports hierarchical
routing through the use
of OSPF areas
 Link State ID field is an
IP network number
LS Age
Link State ID
Advertising Router
LS Sequence Number
LS Checksum
Length
Options LS Type

LS Type 4 - Summary-LSAs (ASBR)
 This originate from Area
Border Routers (ABRs)
 Similar to LS Type 3
 Used when destination is
an Autonomous System
Boundary Router (ASBR)
 The Link State ID is the
AS boundary router’s
OSPF Router ID
LS Age
Link State ID
Advertising Router
LS Sequence Number
LS Checksum
Length
Options LS Type

LS Type 5 - AS-external-LSAs
 Originated by AS boundary
routers and describes
destinations ex-ternal to
the AS.
 Link State ID field specify
an IP network number
LS Age
Link State ID
Advertising Router
LS Sequence Number
LS Checksum
Length
Options LS Type

LS Type 7 - NSSA external-LSAs
 Allows the import of
external routes that
will not be advertised
out of the NSSA
 NSSA - Not So Stubby
Area
LS Age
Link State ID
Advertising Router
LS Sequence Number
LS Checksum
Length
Options LS Type

Router LSA Format - Link ID
Router Type
Link ID
Link Data
Metric
Link Data
0
Number of Links
Link Type # TOS Metrics
Link ID
Metric
Link 1
Link 2,
etc.
Link
type Description Link ID
2 Link to transit network Interface address of
Designated Router
3 Link to stub network IP network number
4 Virtual link Neighbor Router ID
 Originating router’s link
information follows the LSA
header.
 There are four Link IDs
determined by Link Type.
 Type 1 Neighboring router’s Router ID
 Three of this Link ID are
relevant in a broadcast
network

Router LSA Format - Link Data
 For transit and Virtual
Links
 specifies the IP address
of associated router
interface.
 For stub networks
 Specifies the stub
network mask
Router Type
Link ID
Link Data
Metric
Link Data
0
Number of Links
Link ID
Metric
Link 1
Link 2,
etc.

Router LSA Format - Metric
 The cost of using this
router link.
 A user-configurable value
from 1 - 65,535
 The larger the metric, the
less likely (more
expensive) data will be
routed over that particular
link.
 Connections to STUB
networks are allowed to
advertise a metric of zero.
Router Type
Link ID
Link Data
Metric
Link Data
0
Number of Links
Link ID
Metric
Link 1
Link 2,
etc.

Link-State Database (LSDB)
 The collection of all OSPF LSAs received
 Each OSPF router has an identical LSDB
 Gives complete description of the network:
 routers
 network segments
 interconnectivity (how it is interconnected)
 LSDBs are exchanged between neighboring
routers soon after routers discover each
other
 Maintained through a procedure called
reliable flooding

 When two neighbors first start
communicating, they must synchronize their
databases before forwarding traffic over
their shared link to prevent routing loops
from occurring.
LSDB Initial Synchronization
Summit 4
Switch A
Summit 4
Switch B
Synchronize Databases

OSPF-specified Database Exchange
 Procedure used by the routers to
synchronize their databases once the hello
protocol determines a bi-directional
connection between router neighbors.
 During synchronization, the neighbor
routers do three things:
 Forward current LSA headers
 Compares the header received to the LSDB
 Request the full LSA for new or newer headers

Example LSDB Initial Synchronization
Summit 4
Switch A
Summit 4
Switch F
Summit 4
switch c
Summit 4
switch d
Summit 4
switch b
Summit 4
switch e Switches A thru F are
in a stable OSPF
network and have fully
synchronized
databases
OSPF is restarted on
Switch F, forcing
database
synchronization with
switch A.

Example LSDB Initial Synchronization
Summit 4
Switch A
Summit 4
Switch F
OSPF Hello: I heard Switch
A
OSPF Hello
Database Description: Sequence = X
Database Description: Sequence = X+1
LSA header = (router LSA, switch F, 0x80000001)
Database Description: Sequence = X+1
Link State Request Packet for the following LSAs:
(Router LSA, Switch A)
(Router LSA, Switch b)
(Router LSA, Switch c)
(Router LSA, Switch d)
(Router LSA, Switch e)
(Router LSA, Switch F)
Database Description: Sequence = X with 6 LSA headers
(Router LSA, Switch A, 0x80000007)
(Router LSA, Switch b, 0x800000b2)
(Router LSA, Switch c, 0x80000003)
(Router LSA, Switch d, 0x80000021)
(Router LSA, Switch e, 0x80000012)
(Router LSA, Switch F, 0x80000005)
Link State Update packet for the following LSAs:
(Router LSA, Switch A, 0x80000007)
(Router LSA, Switch b, 0x800000b2)
(Router LSA, Switch c, 0x80000003)
(Router LSA, Switch d, 0x80000021)
(Router LSA, Switch e, 0x80000012)
(Router LSA, Switch F, 0x80000005)
Link State Update packet, LSA =
(router LSA, switch F, 0x80000006)
Bidirectionality established
Database Exchange sequence number created
Sequence number incremented, acknowledges previous
exchange pair
empty database description packet used for
acknowledgement
Router requests all LSAs not in its local database
Updated LSA for switch F with larger sequence number

OSPF Database - Reliable Flooding
 LSA Updates are periodically generated by
a router wishing to update a self-originated
LSA because:
 The router’s local state may have changed
 The router wants to delete one of its self-
originated LSAs
 Used to propagate LSA Updates throughout
the routing domain

Reliable Flooding - What Happens
 A router will generate a Link-state Update
packet containing one or more LSAs
 Update is forwarded out all interfaces.
 Neighbor router receives the Update and
compares the LSAs with the LSDB
 More recent LSAs are installed in LSDB
 Acknowledgement is sent back to
originating route
 New Link-state Update containing the LSA is
sent out all interfaces except receiving one.

OSPF Routing Calculations
 With router LSDBs synchronized for all
routers in routing domain
 The router will use Dijkstra’s Shortest Path First
algorithm
 This allows calculation of shortest paths to all
destinations
 Routing table is constructed from the
calculations and includes
 network destinations
 associated costs

Summit 4
Switch C
Summit 1
1
2
8
3 4 5 6 7
Switch D
Summit 48
Switch H
Summit 48
Switch G
Summit 48
Switch F
Summit 1
1
2
8
3 4 5 6 7
Switch E
Summit 48
Switch I
Summit 48
Switch J
Summit 48
Switch K
Summit 48
Switch A
Summit 48
Switch B
1
1
1 1
1
1
5
5
5
5
1
2 2
1 1
3
 Every link carries an associated cost.

Switch I (3, Switch D)
Switch J (3, Switch D)
Switch K (3, Switch D)
Switch F (3, Switch E)
Switch G (3, Switch E)
Switch H (3, Switch E)
Switch E (2, Switch E)
Switch I (3, Switch D)
Switch J (3, Switch D)
Switch K (3, Switch D)
Iteration
Destination Added to
Shortest-Path Tree
Candidate List Destination
(cost, next hops)
Switch A (1, Switch A)
Switch B (1, Switch B)
Switch D (2, Switch D)
Switch C
1
2 Switch A
Switch B (1, Switch B)
Switch B
3
Switch D
4
Switch E
5
Switch I
Switch J
Switch K
Switch F
Switch G
Switch I Empty
6
7
8
9
10
11
Shortest Path First Calculation for Switch "C"

 Applying Dijkstra’s SPF algorithm, Switch C’s routing table
would incorporate the highlighted links
Summit 4
Switch C
Summit 1
1
2
8
3 4 5 6 7
Switch D
Summit 48
Switch H
Summit 48
Switch G
Summit 48
Switch F
Summit 1
1
2
8
3 4 5 6 7
Switch E
Summit 48
Switch I
Summit 48
Switch J
Summit 48
Switch K
Summit 48
Switch A
Summit 48
Switch B
1
1
1 1
1
1
5
5
5
5
1
2 2
1 1
3
Note that Switch A will
never talk directly to
Switch B as long as the
links thru Switch C
remain stable.

 Note how changing a link cost affects the route
calculation for the shortest path
With this configuration,
Switch C now has two
paths of equal cost to
communicate with
Switch J.
Summit 4
Switch C
Summit 1
1
2
8
3 4 5 6 7
Switch D
Summit 48
Switch H
Summit 48
Switch G
Summit 48
Switch F
Summit 1
1
2
8
3 4 5 6 7
Switch E
Summit 48
Switch I
Summit 48
Switch J
Summit 48
Switch K
Summit 48
Switch A
Summit 48
Switch B
5
1
1 1
5
1
3
3
3
5
1
2 4
1 5
3
Communication with
Switch B is no longer
direct, but must routed
thru Switch A.

OSPF Network Types
 Point-to-Point networks
 Serial lines
 Non-broadcast Multi-access (NBMA)
networks
 X.25, ATM
 Point-to-Multipoint networks
 Frame Relay
 Broadcast networks

OSPF Network Type - Broadcast Networks
 A network with more than two attached
devices
 Has the ability to address a single physical
message to all of the attached devices
(broadcast)
10.1.1.1 10.1.1.5
10.1.1.3
10.1.1.4
10.1.1.2

OSPF Network Type - Broadcast Networks
 Only network type supported by Extreme switches
 Other Network Types are for WAN use
10.1.1.1 10.1.1.5
10.1.1.3
10.1.1.4
10.1.1.2

Broadcast Networks Terminology
 DR - Designated Router
 BDR - Backup DR
 DR and BDR Election
 Network LSAs

Broadcast Networks - Designated Router
 Every broadcast network has a Designated
Router (DR) and a Backup Designated
Router (BDR)
 Each router on the network exchanges link
state information only with the DR and BDR.
 This information is used to maintain database
synchronization between the DR and neighbor
routers
 This reduces the amount of traffic otherwise
consumed by routing protocol traffic
 Only a DR generates a LS Type 2 - Network-
LSAs

DR and BDR Election
 First OSPF router on an IP subnet always
becomes the DR
 Second OSPF router always becomes BDR
 If DR or BDR fail, the OSPF router with the
highest Router Priority will replace the BDR
 If two OSPF routers have same Router
Priority, then the OSPF Router ID will break
the tie
 A Router Priority of 0 will prevent an OSPF
router from ever being elected as DR or BDR

Database Synchronization
 An OSPF router will send its Link State
Update (LSU) to the DR and BDR
 The destination IP address for the LSU will be
multicast address 224.0.0.6 (All DRouters).
 The DR will then flood the update to all
OSPF routers
 The destination IP address for the LSU will be
multicast address 224.0.0.5 (All OSPFRouters).

Representing Broadcast Subnet in LSDB
 If an OSPF router included all known routers on
a common subnet in its router-LSA, there would
be n*(n-1) links in the OSPF database.
 By using a new LSA type, the Network-LSA, to
represent the broadcast subnet, the number of
links is reduced from n*(n-1) to n*2.
 Each network LSA has a link to every router-
LSA, and every router-LSA has a link to the
broadcast subnet’s network-LSA.
 DR maintains the network-LSA

Type 2: Network LSAs
 Created in order to
reduce the number of
links in each router’s
resulting LSDB
 Describes the subnet,
all routers on that
network DR identity
LS Age
Link State ID
Advertising Router
LS Sequence Number
LS Checksum
Length
Options LS Type
Network Mask
Attached Router 1
Attached Router 2, etc.

Type 2: Network LSAs
router-LSA
link-state ID
Designated
Router-orginated
network-LSA
router-LSA
link-state ID
router-LSA
link-state ID
router-LSA
link-state ID
Router 1
router-LSA
Router 3
router-LSA
Router 4
router-LSA
Router 2
router-LSA
network-LSA
link-state ID
network-LSA
link-state ID
network-LSA
link-state ID
network-LSA
link-state ID
The network-LSA
helps in database
synchronization,
since a router
having a router-
LSA with a link to
the network-LSA
and vice-versa is
known to have a
database
synchronized with
the Designated
Router.

Building OSPF Networks
 Hierarchical Routing
 OSPF Routing Hierarchy
 OSPF Areas
 OSPF Types of Routers
 Virtual Links
 CLI Commands for OSPF Configuration

Hierarchical Routing
 OSPF implements a two-level
hierarchical routing scheme
 Saves router memory consumed
by the routing table
 Saves router resources when
computing the routing table
 Saves link bandwidth when
distributing routing data

OSPF Areas Defined
 The OSPF hierarchy is maintained through
the deployment of OSPF areas
 Each OSPF area is identified by a 32-bit
Area ID
 Each area consists of a collection of one or
more network segments interconnected by
routers
 An area has its own LSDB consisting of
router-LSAs and network-LSAs
 These LSAs describe area’s topology
 Routing with an area is flat.

Area’s Router-LSA and Network-LSA
 Not flooded beyond the area’s borders
 Detailed knowledge of area’s topology is
hidden from all other areas in the parent
Autonomous System.
Summit 1
1
2
8
3 4 5 6 7
Summit 48 Summit 48
Summit 4
Summit 48 Summit 48 Summit 3
Summit 3
Summit 3
Summit 1
1
2
8
3
4
5
6
7
Summit 48
Summit 48
Summit 4
Summit 48
Summit 48
Summit 3
Summit 3
Summit 3
Area A Area B
Area “A” does not know the internal topology of Area “B” and vice versa.

Area Border Router (ABR)
 Manages inter-area communication
 Attached to two or more areas, running
multiple copies of the basic algorithm
 Maintain LSDBs for each attached area and
an additional copy for the backbone
 Condense the topological information of
their attached areas into Type 3: Summary-
LSAs for distribution to the backbone.
 The backbone in turn distributes the information
to the other areas.

Area Border Router (ABR) cont.
 ABRs can be
configured to
aggregate some or
all of the networks
within its
dependent area
into a single,
summary network
address with a less
discreet network
mask.
g
Summit 1
1
2
8
3 4 5 6 7
Summit 48 Summit 48
Summit 4
Summit 48 Summit 48 Summit 3
Summit 3
Summit 3
10.5.1.0/24
10.5.2.0/24
10.5.3.0/24
10.5.4.0/24
Aggregate!!!
10.5.0.0/16

Types of OSPF Areas
 Normal Area
 Area 0 (Backbone)
 Stub Areas
 Not-So-Stubby-Areas (NSSA)
 Virtual Links

Normal Area
 An area which is not a:
 Stub area
 NSSA
 Can be placed anywhere within the OSPF
routing domain
 Support ASBRs
 Support Virtual Links
 Can distribute external routes

Area 0 (Backbone)
 Is a Normal Area
 Responsible for distributing routing
information between areas
 Consist of
 all area border routers
 networks not contained in any other area
 and their attached routers
 Has an Area ID of 0.0.0.0
 Only one backbone area per AS
 All areas are required to attach directly to
the OSPF backbone area

Stub Area
 For routers with limited resources
 reduce memory and computation requirements
 The LSDB is kept as small as possible
 External route information is not distributed
 Will use default routes to ABRs instead
 Does not support ASBRs
 Does not support virtual links
 Appears to lie on the edge of an OSPF
domain (AS) in configuration

Not-So-Stubby-Area (NSSA)
 Similar to existing OSPF Stub Area with two
additional capabilities
 External routes originating from ASBR connect-
ed to NSSA can be advertised within
 External routes originating from NSSA can be
propagated to other areas, including the
backbone.

OSPF Defines Three types of Routers
 Internal Router (IR)
 Has all of its interfaces within the same area
 Area Border Router (ABR)
 Autonomous System Boundary Router
(ASBR)

OSPF Hierarchical Components
OSPF Router Types Displayed
Area 3
R 13
R 1 R 2
R 3
R 4
R 6
R 7
R 9
R 8
R 5
Area 2
Area 1
Area 3
Autonomous S ystem
R 11
R 10
R 12
ABR ABR
ABR
ASBR
*All other routers that are not labeled ASBR or ABR are Internal Routers
Internet

Virtual Links
 Used when a new area is introduced that
does not have a direct physical attachment
to the backbone
 Provides a logical path between the ABR of
the disconnected area and the backbone
 A virtual link is established between two
ABRs that have a common area, with one
ABR connected to the backbone

OSPF Configuration Example
E
E
E
E
E
E
E
E
Area 0.0.0.0
Area 0.0.0.5
NSSA
RIP
Cloud
Area 0.0.0.4
STUB
Area 0.0.0.3
Normal
Area 0.0.0.1
Normal
Area 0.0.0.2
Normal
Internet
BGP
E
VL
VL

Configuring OSPF
 Must have a unique router ID for each switch
 Recommend manually setting the router ID
of the switches participating in OSPF
 Simplifies router management
 Prevents corruption of virtual links
 Do not use 0.0.0.0 as a router ID

OSPF CLI Commands
 enable/disable ospf
 config ospf add/delete vlan
 create/delete ospf area
 config ospf vlan area
 show ospf area
 show ospf interfaces

CLI Command - enable/disable ospf
enable ospf
disable ospf
Enable or disable OSPF for the whole router.
Default is disabled.

CLI Command - config ospf add/del vlan
config ospf add vlan [<name> | all]
config ospf delete vlan [<name> | all]
 Enables or disables OSPF on one or all VLANs
(router interfaces).
 The default setting is disabled.

CLI Command - create/del ospf area
create ospf area <areaid>
delete ospf area [<areaid> | all]
 Create or delete an OSPF area. Area 0.0.0.0
does not need to be created. It exists by default.
It also cannot be deleted.
 Once an OSPF area is removed, the associated
OSPF area and OSPF interface information will
also be removed.

CLI Command - config ospf vlan area
config ospf vlan <name> area <areaid>
 Associates a VLAN (router interface) with/from
an OSPF area. The area must already be
defined. All router interfaces must have an
associated OSPF area.
 By default, all router interfaces are associated
with area 0.0.0.0 (backbone).

CLI Command - show ospf
show ospf
 Displays global OSPF information.
show ospf area {<areaid>}
 Displays information about a particular OSPF
area, or all OSPF areas.

Example: show ospf area
OSPF_Switch4: show ospf area
Area: 0.0.0.0 Stub: FALSE Rtr Id: 20.20.20.20
Spf Runs: 48 Num ABR: 6 Num ASBR: 0 Num LSA: 43 LSA Chksum:0x170863
Interfaces:
IP addr Ospf State DR IP addr BDR IP addr
10.0.2.1 /24 E DOWN 0.0.0.0 0.0.0.0
10.0.1.1 /24 E BDR 10.0.1.2 10.0.1.1
Inter-Area route Filter: None
External route Filter: None
Configured Address Ranges:
Area: 10.11.0.0 Stub: FALSE Rtr Id: 20.20.20.20
Spf Runs: 21 Num ABR: 2 Num ASBR: 0 Num LSA: 35 LSA Chksum:0x16c3de
Interfaces:
IP addr Ospf State DR IP addr BDR IP addr
10.11.1.1 /24 E DR 10.11.1.1 10.11.1.2
Inter-Area route Filter: None
External route Filter: None
Configured Address Ranges:

CLI Command - show ospf interfaces
show ospf interfaces {vlan <name> | area <areaid>|all}
Displays information about one or all OSPF area, or all
OSPF areas.

Example: show ospf interface
Summit4: sh ospf interface
Interface(rif4): 10.15.1.1/24 Vlan: norm151 Ospf: ENABLED Router: ENABLED
AreaId: 10.15.0.0 RtId: 20.20.20.20 Cost: 1 Pri: 1 Transit Delay: 1
Hello Interval: 10s Rtr Dead Time: 40s Retransmit Interval: 5s
Authentication: NONE
State: BDR Number of events: 1
DR RtId: 30.30.30.30 DR IP addr: 10.15.1.3 BDR IP addr: 10.15.1.1
Neighbours:
RtrId: 10.10.10.10 IpAddr: 10.15.1.2 Pri: 1
State: FULL Dr: 10.15.1.3 BDR: 10.15.1.1 Dead Time: 7
RtrId: 30.30.30.30 IpAddr: 10.15.1.3 Pri: 1

Laboratory Exercise
 Lab4 - OSPF Configuration I

Lab4 - Network Topology
OSPF_LAB_5
OSPF_LAB_2
OSPF_LAB_6 OSPF_LAB_4
OSPF_LAB_1
OSPF_LAB_3
OSPF_LAB_5
OSPF_LAB_2
OSPF_LAB_1
OSPF_LAB_3
.2
.1
Normal
10.13.0.0
NORM131
10.13.1.0/24
.2
.1
Normal
10.11.0.0
NORM111
10.11.1.0/24
.2
.1
Normal
10.17.0.0
NORM151
10.17.1.0/24
.2
.1
Normal
10.19.0.0
NORM171
10.19.1.0/24
Backbone
0.0.0.0
BBONE1
10.0.1.0/24
.1
.2
Port 18
NORM131
Port 21
NORM111
Port 21
NORM131
Port 18
NORM111
Port 19
BBONE1
Port 19
BBONE1
Port 18
NORM191
Port 18
NORM171
Port 21
NORM191
Port 21
NORM171

More OSPF Configuration
 config ospf add virtual-link
 config ospf delete virtual-link
 show ospf virtual-link

CLI Command - config ospf add virtual-link
config ospf add virtual-link <routerid> <areaid>
config ospf delete virtual-link <routerid> <areaid>
 Adds or deletes a virtual link connected to another
area border router (ABR).
 Specify the following:
 routerid -- Far-end router ID.
 Areaid -- Transit area used for connecting the
two end-points. The transit area cannot be the
backbone (0.0.0.0).

CLI Command - show ospf virtual-link
show ospf virtual-link {<areaid><routerid> | all}
Displays virtual link information about a particular
router or all routers. Default is all. Contains:
 Area ID and neighbor router ID
 Receive interval, transit delay, Hello interval, and
dead interval.
 Authentication configuration
 Virtual link type and number of events
 Neighbor router ID, IP address, and priority
 Link state, DR ID, BDR ID, and dead time

Example: show ospf virtual-link
OSPF_LAB_2:19 # show ospf virtual-link
AreaId: 10.15.0.0 NbrRouterId: 10.10.10.10
Rxmit Interval: 5 Transit Delay: 1 Hello Interval: 10 Dead Interval: 40
Auth Type: NONE
State: P2P Number of Events: 3
RtrId: 10.10.10.10 IpAddr: 10.15.1.2 Pri: 1
AreaId: 10.15.0.0 NbrRouterId: 30.30.30.30
Rxmit Interval: 5 Transit Delay: 1 Hello Interval: 10 Dead Interval: 40
Auth Type: NONE
State: P2P Number of Events: 1
RtrId: 30.30.30.30 IpAddr: 10.15.1.3 Pri: 1

Laboratory Exercise
 Lab5 - OSPF Configuration II

Lab5 - Network Topology 1
Normal
10.13.0.0
NORM131
10.13.1.0/24
Normal
10.11.0.0
NORM111
10.11.1.0/24
Normal
10.19.0.0
NORM191
10.19.1.0/24
Normal
10.17.0.0
NORM171
10.17.1.0/24
Backbone
0.0.0.0
BBONE1
10.0.1.0/24
.2
.1
.2
.1
.2
.1
.2
.1
.1
.2
Port 18
NORM121
Port 21
NORM121
Port 21
NORM121
Port 18
NORM121
Port 19
BBONE1
Port 19
BBONE1
Port 18
NORM171
Port 18
NORM171
Port 21
NORM171
Port 21
NORM171
OSPF_LAB_5
OSPF_LAB_2
OSPF_LAB_1
OSPF_LAB_3
OSPF_LAB_2
OSPF_LAB_1
OSPF_LAB_3
OSPF_LAB_5
Network Physical
Normal
10.21.0.0
NORM211
10.21.1.0/24
.1
.3 .2
Normal
10.15.0.0
NORM151
10.15.1.0/24
.1
.3 .2
Port 17
NORM151
Port 22
NORM151
Port 17
NORM151
Port 22
NORM151
Port 17
NORM211
Port 22
NORM211
Port 17
NORM211
Port 22
NORM211

Lab5 - Network Topology 2
Backbone
0.0.0.0
BBONE1
10.0.1.0/24
.1
.2
Normal
10.21.0.0
NORM211
10.21.1.0/24
.1
.3 .2
.2
.1
Normal
10.19.0.0
NORM191
10.19.1.0/24
.2
.1
Normal
10.17.0.0
NORM171
10.17.1.0/24
.2
.1
Normal
10.11.0.0
NORM111
10.11.1.0/24
.2
.1
Normal
10.13.0.0
NORM131
10.13.1.0/24
Normal
10.15.0.0
NORM151
10.15.1.0/24
.1
.3 .2
Port 17
NORM151
Port 22
NORM151 Port 18
NORM121
Port 21
NORM121
Port 21
NORM121
Port 18
NORM121
Port 17
NORM151
Port 22
NORM151
Port 19
BBONE1
Port 19
BBONE1
Port 17
NORM211
Port 22
NORM211
Port 17
NORM211
Port 22
NORM211
Port 18
NORM171
Port 18
NORM171
Port 21
NORM171
Port 21
NORM171
OSPF_LAB_5
OSPF_LAB_2
OSPF_LAB_1
OSPF_LAB_3
OSPF_LAB_2
OSPF_LAB_1
OSPF_LAB_3
OSPF_LAB_5
Virtual Links
Virtual Links
Network Physical

More OSPF Configuration - Areas
 config ospf area normal
 config ospf area stub
 config ospf area nssa
 show ospf

CLI Command - config ospf area normal
config ospf area <areaid> normal
 Configure an OSPF area as a normal area
 Default area type is normal
 Area 0.0.0.0 can only be normal

CLI Command - config ospf area stub
config ospf area <areaid> stub
[summary|nosummary] stub-default-cost <cost>
 Configures an OSPF area as a stub area.
 Stub-default-cost is the the cost of the default
summary-LSA that the router should advertise into the
area

CLI Command - config ospf area nssa
config ospf area <areaid> nssa
[summary|nosummary] stub-default-cost
<cost> {translate}
 Configures an OSPF area as a NSSA.
 Stub-default-cost is the the cost of the default
summary-LSA that the router should advertise
into the area
 Translate option: determines whether type 7
LSAs are translated into type 5 LSAs.

CLI Command - show ospf
show ospf
Display global OSPF information:
 Router ID
 OSPF state
 Is router an autonomous system boundary router (Y/N)?
 Is router an area border router (Y/N)?
 Number of external LSAs processed
 External LSA checksum
 Number of originating new LSAs
 Number of received new LSAs
 Shortest Path First hold time

Example: show ospf
Summit4: show ospf
Router Id OSPF ASBR ABR ExtLSA ExtLSACsum OrigNewLSA RxNewLSA
SpfHoldTime
20.20.20.20 E NO YES 0 0x0 14694 20634 3
RouterId Selection: User Configured Export Static: Disabled
Export Static: Disabled
Export Rip: Disabled
ASBR route Filter: None

Laboratory Exercise
 OSPF Lab6
 Utilizing the CLI Commands:
 config ospf area normal
 config ospf area stub
 show ospf

Backbone
0.0.0.0
BBONE1
10.0.1.0/24
.1
.2
.2
.1
Normal
10.17.0.0
NORM171
10.17.1.0/24
.2
.1
Normal
10.19.0.0
NORM191
10.19.1.0/24
Normal
10.21.0.0
NORM211
10.21.1.0/24
NORM212
10.21.2.0/24
NORM213
10.21.3.0/24
NORM214
10.21.4.0/24
.1
.3 .2
.2
.1
Normal
10.13.0.0
NORM131
10.13.1.0/24
.2
.1
Normal
10.11.0.0
NORM111
10.11.1.0/24
Port 18
NORM131
Port 21
NORM111
Port 21
NORM131
Port 18
NORM111
Port 17
NORM151
Port 22
NORM151
Port 17
NORM151
Port 22
NORM151
Port 19
BBONE1
Port 19
BBONE1
Port 17
NORM211
Port 22
NORM211
Port 17
NORM211
Port 22
NORM211
Port 18
NORM191
Port 18
NORM171
Port 21
NORM191
Port 21
NORM171
OSPF_LAB_5
OSPF_LAB_2
OSPF_LAB_1
OSPF_LAB_3
Stub
10.12.0.0
STUB121
10.12.1.1/24
STUB122
10.12.2.1/24
STUB123
10.12.3.1/24
STUB124
10.14.2.1/24
Stub
10.14.0.0
STUB141
10.14.1.1/24
STUB142
10.14.2.1/24
STUB143
10.14.3.1/24
STUB144
10.14.4.1/24
Normal
10.15.0.0
NORM151
10.15.1.0/24
NORM152
10.15.2.0/24
NORM153
10.15.3.0/24
NORM154
10.15.4.0/24
.1
.3 .2
OSPF_LAB_2
OSPF_LAB_1
OSPF_LAB_3
Stub
10.20.0.0
STUB201
10.20.1.1/24
STUB202
10.20.2.1/24
STUB203
10.20.3.1/24
STUB204
10.20.2.1/24
Stub
10.18.0.0
STUB181
10.18.1.1/24
STUB182
10.18.2.1/24
STUB183
10.18.3.1/24
STUB184
10.18.2.1/24
Virtual Links
Virtual Links
Port1 x-over to Port2
Port1 x-over to Port2 Port1 x-over to Port2
OSPF_LAB_5

More OSPF Configuration Commands
 config ospf routeid
 config ospf area add range
 config ospf vlan area cost
 config ospf vlan area priority
 *enable iproute sharing
 enable/disable ospf exportstatic type
 config ospf vlan area virtual link authentication
 config ospf vlan area virtual link timer
 config ospf spf-hold-time
 show ospf lsdb

CLI Command - config ospf area add range
config ospf area <areaid> add range
<ipaddress> <mask> [advertise | noadvertise]
{type 3|type 7}
config ospf area <areaid> delete range
<ipaddress> <mask>
 Configures or deletes a range of IP addresses in an
OSPF area.
 On add, and if advertised, the range is exported as a
single LSA by the ABR.

CLI Command - config ospf … cost
config ospf [vlan <name> | area <areaid> | all]
cost <number>
 Configures the cost (metric) of one or all
interface(s).
 The default cost of an interface is 1.
 The maximum cost is 65,535.

CLI Command - config ospf … priority
config ospf [vlan <name> | area <areaid> | all]
priority <number>
 Configures the priority used in the designated
router-election algorithm for one or all IP
interface(s) or for all the interfaces within the
area.
 The range is 0 - 255
 The Default priority setting is 1
 A value of 0 disqualifies the router from election

CLI Command - enable iproute sharing
enable iproute sharing
 Enables load sharing if multiple routes to the
same destination are available (equal cost
multipath)
 Only paths with the same lowest cost are
shared.

CLI Command - enable/disable ospf exportstatic
enable ospf export static cost {<metric>}
[ase-type-1|ase-type-2] {tag <number>}
disable ospf export static
 Enable/disables the distribution of static routes
into the OSPF domain.
 The default tag number is 0.

CLI Command - config ospf … authentication
config ospf [vlan <name> | area <areaid> | virtual-link
<routerid> <areaid>] authentication
[simple-password <password> | md5 <md5_key_id>
<md5_key> | none]
 Configure OSPF authentication information for one
interface or all the interfaces in an AREA.
 When the OSPF AREA ID is specified, then the
authentication information is applied to all the OSPF
interfaces within the area.

CLI Command - config ospf … timer
config ospf [vlan <name> | area <areaid> | virtual-
link <routerid>] timer <retransmission_interval>
<transmission_delay> <hello_interval>
<dead_interval>
 Configures the timers for one interface or all the
interfaces in the same OSPF area.
 The following default, min, and max values (in seconds) are used:
Variable Default Min Max
RETRANSMISSION 5 0 3600
DELAY 1 0 3600
HELLO 10 1 65535
DEAD INTERVAL 40 1 2147483647

CLI Command - config ospf spf-hold-time
config ospf spf-hold-time {<seconds>}
 Configures the minimum number of seconds
between Shortest Path First (SPF) recalculations.
 The default setting is 3 seconds.

CLI Command - show ospf lsdb
show ospf lsdb {detail} area [<areaid> | all]
[router | network | summary-net |
summary-asb | as_external | external-type 7 | all}
 Displays a table of the current LSDB.
 The user can filter the display using either area ID,
the remote router's router ID, or the link state ID.
 Default is all with no detail.
 If detail is specified, each entry includes complete
LSA information

Example: show ospf lsdb
OSPF_LAB_2:18 # show ospf lsdb area all all
Router LSAs for area 0.0.0.0
Link State ID Adv Router Seq# Age Chksum #Links
-------------------------------------------------------------
10.10.10.10 10.10.10.10 0x8000011d 1227 0xafc6 1
20.20.20.20 20.20.20.20 0x80006754 510 0x835f 3
30.30.30.30 30.30.30.30 0x800040a9 1245 0xf018 1
40.40.40.40 40.40.40.40 0x80000169 450 0x6e4c 1
50.50.50.50 50.50.50.50 0x800001ab 1279 0x7f83 3
60.60.60.60 60.60.60.60 0x8000016c 461 0x8095 1
Network LSAs for area 0.0.0.0
Link State ID Adv Router Seq# Age Chksum
-------------------------------------------------------------
10.0.1.2 50.50.50.50 0x80000169 1273 0xb14f
Summary LSAs for area 0.0.0.0
Link State ID Adv Router Seq# Age Chksum
-------------------------------------------------------------
10.11.1.0 10.10.10.10 0x80000114 1230 0x dfc
10.11.1.0 20.20.20.20 0x8000011b 1250 0xd109
10.12.0.0 10.10.10.10 0x80000109 1018 0x22f2
10.13.1.0 20.20.20.20 0x80000194 1250 0xc698

Laboratory Exercise
 OSPF Lab7

Stub
10.20.0.0
STUB201
10.20.1.1/24
STUB202
10.20.2.1/24
STUB203
10.20.3.1/24
STUB204
10.20.2.1/24
.2
.1
Normal
10.19.0.0
NORM191
10.19.1.0/24
Stub
10.18.0.0
STUB181
10.18.1.1/24
STUB182
10.18.2.1/24
STUB183
10.18.3.1/24
STUB184
10.18.2.1/24
.2
.1
Normal
10.17.0.0
NORM171
10.17.1.0/24
Normal
10.21.0.0
NORM211
10.21.1.0/24
NORM212
10.21.2.0/24
NORM213
10.21.3.0/24
NORM214
10.21.4.0/24
.1
.3 .2
Stub
10.12.0.0
STUB121
10.12.1.1/24
STUB122
10.12.2.1/24
STUB123
10.12.3.1/24
STUB124
10.14.2.1/24
.2
.1
Normal
10.11.0.0
NORM111
10.11.1.0/24
Stub
10.14.0.0
STUB141
10.14.1.1/24
STUB142
10.14.2.1/24
STUB143
10.14.3.1/24
STUB144
10.14.4.1/24
.2
.1
Normal
10.13.0.0
NORM131
10.13.1.0/24
Normal
10.15.0.0
NORM151
10.15.1.0/24
NORM152
10.15.2.0/24
NORM153
10.15.3.0/24
NORM154
10.15.4.0/24
.1
.3 .2
Port1 x-over to Port2 Port1 x-over to Port2
Port 17
NORM211
Port 22
NORM211
Port 18
NORM191
Port 18
NORM171
Port 21
NORM191
Port 21
NORM171 Port 17
NORM211
Port 22
NORM211
Port 19
BBONE1
Port 19
BBONE1
Port 17
NORM151
Port 22
NORM151
Port 18
NORM131
Port 21
NORM111
Port 21
NORM131
Port 18
NORM111
Port 17
NORM151
Port 22
NORM151
Virtual Links
Virtual Links
Network Physical
Backbone
0.0.0.0
BBONE1
10.0.1.0/24
BBONE2
10.0.2.0/24
.1
.2
OSPF_LAB_5
OSPF_LAB_2
OSPF_LAB_1
OSPF_LAB_3
OSPF_LAB_2
OSPF_LAB_1
OSPF_LAB_3
OSPF_LAB_5
Port 20
BBONE2
Port 20
BBONE2
Summarize
to
10.14.0.0/16
Summarize
to
10.12.0.0/16
Summarize
to
10.18.0.0/16
Summarize
to
10.20.0.0/16
Equal-Cost Multipath
Summarize
to
10.21.0.0/16
Summarize
to
10.15.0.0/16

Summary
 Define OSPF, features, advantages over RIP
 Describe OSPF LSA, format and Types
 Define LSDB, Initial synchronization,
database exchange & reliable flooding
 Describe Routing Calculations, supported
network type & Database Synchronization
 Describe how to build OSPF Networks
 Define the OSPF routing, areas, router types
and virtual Links
 Differentiate DR, BDR, Router Election
 OSPF Configuration and Examples
 Lab Exercises

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