Module 3 - Multiarea OSPF Operation pptx

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BSCI Module 3 Lesson 6 - Multiarea OSPF

Operation

 Large OSPF Network Issues

 OSPF LSA Types

 OSPF LSA Types (cont.)

 Interpreting the OSPF LSDB and Routing Table

 Interpreting the Routing Table

 Calculating Costs for E1 and E2 Routes

 Configuring OSPF LSDB Overload Protection

 Changing the Cost Metric

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Large OSPF Network Issues

 Hierarchical area routing separates a large internetwork

into multiple areas When you use this technique, interarea routing still occurs, but many of the internal routing operations, such as SPF calculations, remain within individual areas

– Reduced frequency of SPF calculations

– Smaller routing table

– Reduced LSU overhead

LSA Types

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LSA Type 1 Link Types

Link

1 Point-to-point connection to another

2 Connection to a transit network IP address of DR

3 Connection to a stub network IP network/subnet

number

4 Virtual link Neighboring router ID

The Link ID in the OSPF Database

RouterA# show ip ospf database

OSPF Router with ID (10.0.0.11) (Process ID 1)

Router Link States (Area 0) Link ID ADV Router Age Seq# Checksum Link count

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LSA Type 1: Router LSA

 One router LSA (type 1) for every router in an area:

– Includes list of directly attached links

 Identified by the router ID of the originating router

 Floods within its area only; does not cross ABR

 Link-state ID depends on link type

LSA Type 1: Router LSA

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Type 1: Router LSAs

 The command show ip ospf database router will list all of the Router

LSAs in a database.

LSA Type 2: Network LSA

 Advertised by the DR of the broadcast network

 Floods within its area only; does not cross ABR

 Link-state ID is the DR

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LSA Type 2: Network LSA

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Type 2: Network LSAs

 The command show ip ospf database network is used to observe a

Network LSA.

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LSA Type 3: Summary LSA

 Advertised by the ABR of originating area

 Regenerated by subsequent ABRs to flood throughout

the autonomous system

 By default, routes are not summarized, and type 3 LSA

is advertised for every subnet

 Link-state ID is the network or subnet advertised in the

summary LSA

LSA Type 3: Summary LSA

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Type 3: ABR Summary LSAs

 The command show ip ospf database summary is used to display the

network summary LSAs in the database.

LSA Type 4: Summary LSA

all other areas in the autonomous system.

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Type 4: ASBR Summary LSAs

 The command show ip ospf database asbr-summary is used to display

ASBR Summary LSAs

LSA Type 5: External LSA

other autonomous systems.

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Type 5: Autonomous System External LSAs

 The command show ip ospf data base externaldisplays AS External

LSAs

LSA Types: 6, 7, 8

 Group Membership LSAs are used in an enhancement of OSPF

known as Multicast OSPF (MOSPF) MOSPF routes packets from

a single source to multiple destinations, or group members, which share a class D multicast address Although Cisco supports other multicast routing protocols, MOSPF is not supported as of this writing.

 NSSA External LSAs are originated by ASBRs within

not-so-stubby areas (NSSAs

 External Attributes LSAs were proposed as an alternative to

running Internal BGP (iBGP), to transport BGP information across

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Type 7: Not-So-Stubby Area LSAs

 The command show ip ospf database nssa-externaldisplays NSSA

external LSAs

LSA Operation Example

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LSA Types: 9, 10, 11

 Opaque LSAs are a class of LSAs that consist of a standard LSA

header followed by application-specific information

 The Information field can be used directly by OSPF or indirectly by

other applications to distribute information throughout the OSPF

domain

 Opaque LSAs have been used to add various extensions to OSPF ,

such as traffic engineering parameters for Multiprotocol Label

Switching (MPLS) networks

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Interpreting the OSPF Database

RouterA# show ip ospf database

OSPF Router with ID (10.0.0.11) (Process ID 1)

Router Link States (Area 0) Link ID ADV Router Age Seq# Checksum Link count

ADV Router: Advertising router; the source router of the LSA

Link count: Total number of directly attached links, used only on

router LSAs

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Interpreting the Routing Table

 When an ABR receives summary LSAs, it adds them to

its LSDB and regenerates them into the local area

When an ABR receives external LSAs, it adds them to its LSDB and floods them into the area

Calculating Costs for E1 and E2 Routes

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OSPF LSDB Overload Protection

 Excessive LSAs generated by other routers can drain

local router resources

 This feature can limit the processing of non-self-generated LSAs for a defined OSPF process

max-lsa maximum-number [threshold-percentage]

[warning-only] [ignore-time minutes] [ignore-count count-number]

[reset-time minutes]

Router(config-router)#

The max-lsa Parameters

Parameter Description

maximum-number Maximum number of non-self-generated LSAs that the OSPF process can keep in the OSPF LSBD.threshold-

percentage

(Optional) The percentage of the maximum LSA number, as specified by the

maximum-number argument, at which a warning message is logged The

max-lsa maximum-number [threshold-percentage]

[warning-only] [ignore-time minutes] [ignore-count count-number]

[reset-time minutes]

Router(config-router)#

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ip ospf cost interface-cost

Changing the Cost Metric

 The cost, or metric, is an indication of the overhead to

send packets over an interface Default = (100 Mbps)/(bandwidth in Mbps)

auto-cost reference-bandwidth ref-bw

RouterA(config-if)#

RouterA(config-router)#

 Overrides the default cost calculation Values from 1 to

65535 can be defined

 Sets the reference bandwidth to values other than 100

Mbps (legal values range from 1 to 4,294,967 in Mbps)

 3.6.3 Drag and Drop: OSPF LSA Types

– Upon completion of this activity, the student will be able to identify the different OSPF LSA types.

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Self Check

1 List popular LSA types of OSPF

2 Different between E2 and E1

3 Differentiate O, O IA, O E2/1 in routing table

4 If bandwidth of an interface is 1Gbps, to calculate the

cost for this link, what we must do

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Q and A