Module 5 OSPF Overview and Configuration

1
Module 5OSPF Overview and Configuration
2
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

3
Define OSPF

• Dynamic Routing Protocol
• Link State Protocol
• Employ a distributed database model
• More efficient than RIP

4
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

5
Link-state Protocol

• 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

6
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

7
OSPF Hello Packet Neighbor Discover

• OSPF Hello packets are sent out all of a routers
  interfaces to advertise itself to neighbor
  routers
• A router learns about its neighbors when it
  receives neighbor routers 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

8
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.

9
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.

10
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 routers
  tables.

11
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

12
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.

13
LSA Format - LS Type

• Classifies the LSA according to function
• Type 1
• Type 2
• Type 3
• Type 4
• Type 5
• Type 7

14
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

15
LSA Format - Advertising Router

• The originating routers OSPF router ID
• In practice, this is one of the routers IP
  address

16
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.

17
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

18
LS Type 1 - Router-LSAs

• Generated by each OSPF router
• It describes the routers set of active
  interfaces, its associated cost and any neighbor
  information
• Link State ID is set to the routers OSPF Router
  ID
• Flooded throughout a single area only

19
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

20
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

21
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 routers OSPF Router ID
22
LS Type 5 - AS-external-LSAs
Originated by AS boundary routers and describes
destinations external to the AS. Link State ID
field specify an IP network number
23
LS Type 7 - NSSA external-LSAs

• Allows the import of external routes that will
  not be advertised out of the Not So Stubby Area
  (NSSA)
• Functionally identical to Type 5 for a Normal Area

24
Router LSA Format - Link ID

• Originating routers link information follows the
  LSA header.
• There are four Link IDs determined by Link Type.
• Three of this Link ID are relevant in a broadcast
  network

25
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

26
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.

27
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

28
LSDB Initial Synchronization

• When two neighbors first start communicating,
  they must synchronize their databases before
  forwarding traffic over their shared link to
  prevent routing loops from occurring.

29
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

30
Example LSDB Initial Synchronization
Switches A through F are in a stable OSPF network
and have fully synchronized databases
OSPF is restarted on Switch F, forcing database
synchronization with switch A.
31
Example LSDB Initial Synchronization
32
OSPF Database - Reliable Flooding

• LSA Updates are periodically generated by a
  router wishing to update a self-originated LSA
  because
• The routers 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

33
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.

34
OSPF Routing Calculations

• With router LSDBs synchronized for all routers in
  routing domain
• The router will use Dijkstras 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

35
OSPF Routing Calculations

• Every link carries an associated cost.

36
OSPF Routing Calculations
37
OSPF Routing Calculations

• Applying Dijkstras SPF algorithm, Switch Cs
  routing table would incorporate the highlighted
  links

Note that Switch A will never talk directly to
Switch B as long as the links thru Switch C
remain stable.
38
OSPF Routing Calculations

• 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.
Communication with Switch B is no longer direct,
but must routed thru Switch A.
39
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

40
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)

41
OSPF Network Type - Broadcast Networks

• Only network type supported by Extreme switches
• Other Network Types are for WAN use

42
Broadcast Networks Terminology

• DR - Designated Router
• BDR - Backup DR
• DR and BDR Election
• Network LSAs

43
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

44
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

45
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).

46
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 n2.
• Each network LSA has a link to every router-LSA,
  and every router-LSA has a link to the broadcast
  subnets network-LSA.
• DR maintains the network-LSA

47
Type 2 Network LSAs

• Created in order to reduce the number of links in
  each routers resulting LSDB
• Describes the subnet, all routers on that network
  DR identity

48
Type 2 Network LSAs
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.
49
Building OSPF Networks

• Hierarchical Routing
• OSPF Routing Hierarchy
• OSPF Areas
• OSPF Types of Routers
• Virtual Links
• CLI Commands for OSPF Configuration

50
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

51
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 areas topology
• Routing with an area is flat.

52
Areas Router-LSA and Network-LSA

• Not flooded beyond the areas borders
• Detailed knowledge of areas topology is hidden
  from all other areas in the parent Autonomous
  System.

Area A does not know the internal topology of
Area B and vice versa.
53
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.

54
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.

55
Types of OSPF Areas

• Normal Area
• Area 0 (Backbone)
• Stub Areas
• Not-So-Stubby-Areas (NSSA)
• Virtual Links

56
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

57
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 ABRs are required to attach directly to the
  OSPF backbone area

58
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

59
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.

60
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)

61
OSPF Hierarchical ComponentsOSPF Router Types
Displayed
Internet
ABR
ABR
ASBR
ABR
All other routers that are not labeled ASBR or
ABR are Internal Routers
62
Virtual Links

• Used when a new ABR 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

63
OSPF Configuration Example
64
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
• Must not use 0.0.0.0 as a router ID

65
OSPF CLI Commands

• enable/disable ospf
• config ospf add/delete vlan
• create/delete ospf area
• config ospf vlan area
• config ospf routerid
• show ospf area
• show ospf interfaces

66
CLI Command - enable/disable ospf

• enable ospf
• disable ospf
• Enable or disable OSPF for the whole router.
  Default is disabled.

67
CLI Command - config ospf add/del vlan

• config ospf add vlan ltnamegt all
• config ospf delete vlan ltnamegt all
• Enables or disables OSPF on one or all VLANs
  (router interfaces).
• The default setting is disabled.

68
CLI Command - create/del ospf area

• create ospf area ltareaidgt
• delete ospf area ltareaidgt 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.

69
CLI Command - config ospf vlan area

• config ospf vlan ltnamegt area ltareaidgt
• 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).

70
CLI Command - show ospf

• show ospf
• Displays global OSPF information.
• show ospf area ltareaidgt
• Displays information about a particular OSPF
  area, or all OSPF areas.

71
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 Chksum0x170863 Interf
aces 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 Chksum0x16c3de 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
72
CLI Command - show ospf interfaces

• show ospf interfaces vlan ltnamegt area
  ltareaidgtall
• Displays information about one or all OSPF area,
  or all OSPF areas.

73
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 State FULL Dr 10.15.1.3 BDR
10.15.1.1 Dead Time 6
74
Laboratory Exercise

• Lab 5 - OSPF Configuration I

75
Lab 5 - Network Topology
76
More OSPF Configuration

• config ospf add virtual-link
• config ospf delete virtual-link
• show ospf virtual-link

77
CLI Command - config ospf add virtual-link

• config ospf add virtual-link ltrouteridgt ltareaidgt
• config ospf delete virtual-link ltrouteridgt
  ltareaidgt
• 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).

78
CLI Command - show ospf virtual-link

• show ospf virtual-link ltareaidgtltrouteridgt 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

79
Example show ospf virtual-link
OSPF_LAB_219 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 State FULL Dr
0.0.0.0 BDR 0.0.0.0 Dead Time 9 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 State FULL Dr
0.0.0.0 BDR 0.0.0.0 Dead Time 7
80
Laboratory Exercise

• Lab 6 - OSPF Configuration II

81
Lab 6 - Network Topology 1
82
Lab 6 - Network Topology 2
83
More OSPF Configuration - Areas

• config ospf area normal
• config ospf area stub
• config ospf area nssa
• show ospf

84
CLI Command - config ospf area normal

• config ospf area ltareaidgt normal
• Configure an OSPF area as a normal area
• Default area type is normal
• Area 0.0.0.0 can only be normal

85
CLI Command - config ospf area stub

• config ospf area ltareaidgt stub summarynosummary
  stub-default-cost ltcostgt
• 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

86
CLI Command - config ospf area nssa

• config ospf area ltareaidgt nssa summarynosummary
  stub-default-cost ltcostgt 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.

87
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

88
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

89
Laboratory Exercise

• OSPF Lab 7
• Utilizing the CLI Commands
• config ospf area normal
• config ospf area stub
• show ospf

90
Lab 7 - Network Topology
91
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 export
• config ospf vlan area virtual link authentication
  
• config ospf vlan area virtual link timer
• config ospf spf-hold-time
• show ospf lsdb

92
CLI Command - config ospf routerid

• config ospf routerid automatic ltrouteridgt
• Configures the OSPF router ID.
• If automatic is specified, the switch uses the
  largest IP interface address since OSPF was
  enable as the OSPF router ID. The default setting
  is automatic.

93
CLI Command - config ospf area add range

• config ospf area ltareaidgt add range ltipaddressgt
  ltmaskgt advertise noadvertise type 3type 7
• config ospf area ltareaidgt delete range
  ltipaddressgt ltmaskgt
• 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.

94
CLI Command - config ospf cost

• config ospf vlan ltnamegt area ltareaidgt all
  cost ltnumbergt
• Configures the cost (metric) of one or all
  interface(s).
• The default cost of an interface is 1.
• The maximum cost is 65,535.

95
CLI Command - config ospf priority

• config ospf vlan ltnamegt area ltareaidgt all
  priority ltnumbergt
• 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

96
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.
• The default setting is disabled.

97
CLI Command - enable/disable ospf export

• enable ospf export static rip cost metric
  ase-type-1 ase-type-2 tag ltnumbergt
• disable ospf export static rip
• Enable/disables the distribution of static or RIP
  routes into the OSPF domain.
• The default tag number is 0.
• The default setting is disabled.

98
CLI Command - config ospf authentication

• config ospf vlan ltnamegt area ltareaidgt
  virtual-link ltrouteridgt ltareaidgt
  authentication
• simple-password ltpasswordgt md5 ltmd5_key_idgt
  ltmd5_keygt 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.

99
CLI Command - config ospf timer

• config ospf vlan ltnamegt area ltareaidgt
  virtual-link ltrouteridgt timer ltretransmission_int
  ervalgt lttransmission_delaygt lthello_intervalgt
  ltdead_intervalgt
• 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
100
CLI Command - config ospf spf-hold-time

• config ospf spf-hold-time ltsecondsgt
• Configures the minimum number of seconds between
  Shortest Path First (SPF) recalculations.
• The default setting is 3 seconds.

101
CLI Command - show ospf lsdb

• show ospf lsdb detail area ltareaidgt 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

102
Example show ospf lsdb
OSPF_LAB_218 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
103
Laboratory Exercise

• OSPF Lab 8

104
Lab 8 - Network Topology
105
Laboratory Exercise

• Redistribution Lab 9

106
Lab 9 - Network Topology
107
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