OTA058002 OSPF Protocol Introduction ISSUE1.00

HUAWEI TECHNOLOGIES CO., LTD.

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OTA058002 OSPF Protocol Introduction

ISSUE 1.00

HUAWEI TECHNOLOGIES CO., LTD. Page 2All rights reserved

Upon completion of this course, you will be

able to:

Understand the basis of OSPF

protocol

Understand the calculation methods of

OSPF

Grasp the features of OSPF

Grasp the method of area division


Chapter 1 Basis of OSPF protocolChapter 1 Basis of OSPF protocol

Chapter 2 OSPF routing calculation method Chapter 2 OSPF routing calculation method

Chapter 3 Networking features with OSPFChapter 3 Networking features with OSPF

Chapter 4 Area division of OSPFChapter 4 Area division of OSPF


Overview

OSPF: Open Shortest Path First

Gathering and flooding network link information to generate the

route information of transport plane and control plane in ASON

network.


Overview

Key features of OSPF:

No route self-loop

Adaptable to large-scale networks

Fast route update and convergence

Supporting equivalent value route

Supporting area division

Supporting multicast


Basic Concepts

Router ID (Node ID)

A 32-bit number that uniquely identifies this router in the AS

Number of the Protocol

The protocol number of OSPF Protocol is 89

IP Header(Protocol #89)

OSPF Packet



Chapter 2 OSPF routing calculation methodChapter 2 OSPF routing calculation method




Network Topology

Network topology is described by OSPF through the link status

FR/X.25

EthernetEthernet

PPP


Process

LSDB

LSA of RTA

LSA of RTB

LSA of RTC

LSA of RTD

(2)LSDB of each router (3)Weighted directional figure

obtained from the LSDB

C

A B

D

1

2

3

5

C

A B

D

1

2

3

C

A B

D

1

2

3

C

A B

D

1

2

3

C

A B

D

1

2

3

(1)Network Topology

(4) Each router calculates the shortest path tree by taking itself as the root node

RTA RTB

RTC

RTD


OSPF Packets

HELLO Packet

Discover and maintain neighbors and vote out DR and BDR

DD Packet

Summarize database contents

LSR Packet

Database download

LSU Packet

Database update

LSAck Packet

Flooding acknowledgment


Neighbor State Machine

Down

Attempt Init

2-way ExStart Exchange

Loading

Full


Adjacency Relationship Establishment

Down DownHello( DR = 0.0.0.0,Neighbors Seen = 0)Hello( DR = RT2,Neighbors Seen = RT1) Init

DD (Seq = x,I = 1, M = 1, MS = 1)DD (Seq = y,I = 1, M = 1, MS = 1)DD (Seq = y,I = 0, M = 1, MS = 0)

DD (Seq = y+1,I = 0, M = 1, MS = 1)DD (Seq = y+1,I = 0, M = 1, MS = 0)

ExStartExStart

ExchangeExchange

DD (Seq = y+n,I = 0, M = 0, MS = 1)DD (Seq = y+n,I = 0, M = 0, MS = 0)Loading

FullLS RequestLS UpdateLS AckFull

RT1 RT2







DR Vote

A B C

D E

Network Topology

A

ED

CB

(DR)A

ED

CB

Adjacency Relationship without DR Adjacency Relationship with DR


Route

M= n(n-1)/2 = 28

M= (n-2)×2+1 = 13

DR

BDR

Routes without DR Routes with DR


NBMA and Point-to-Multipoint

NBMA: Full meshed Point-to-Multipoint: Partial meshed


Network Types

Broadcasting （ Ethernet ）

NBMA（ Frame Relay, X.25 ）

Point-to-Multipoint（ Frame Relay, X.25)

Point-to-Point (PPP)







Problems in Huge network

LSDB is very large to occupy lots of memory space.

Calculating the spanning tree increases CPU burden.

It needs a longer time to synchronize the LSDB in AS.

The network topology changes frequently.


Area Division

Area0

Area1 Area3

If the network is too big, we need to divide it into several areas.


Inter-area Route Calculation

172.18.141.0/24 192.178.14.0/28

Type = 3

192.178.14.0

Mask = 255.255.255.240

Metric = 120

Type = 3

172.18.141.0

Mask = 255.255.255.0

Metric = 91

Area 0 Area 3

The method of calculating route among areas is different with that of inner-domain.


Backbone Area and Virtual Connection

Area 0 Area 12 Area 19

Virtual Link

RTA RTB

To prevent the routs loop-back, we use backbone area and virtual connection


External Communication

ASBRRouter ID = 1.2.3.4

10.53.11.0/24

Type = 5

10.53.11.0

Mask=255.255.255.0Metric = 10

Type = 4

1.2.3.4

Mask = 0.0.0.0Metric = 89

Area 0 Area 2

BGP

Communicate with external routers through ASBR


STUB Area and Route Aggregation

Area 0

Area 12 Area 19

Virtual Link

Area 8

19.1.1.0/24

19.1.3.0/24

19.1.2.0/24

RTA


LSA Classification

Router-LSA:

Created by each router

Network-LSA:

Created by DR

Net-Summary-LSA:

Created by ABR

Asbr-Summary-LSA :

Created by ABR

AS-External-LSA :

Created by ASBR


Network types and Router Classification

Networks:

Broadcast, NBMA, Point-to-Point and Point-to-Multipoint

Routers :

IAR, ABR, BBR and ASBR

Status of interface :

DR, BDR, DROther and point-to-point


OSPF Application

Network size:

Medium or large network with more than 10 routers

Network topology:

Mesh

Other request:

Route convergence finished within very short time and low network

overhead

Equipment:

High CPU processing ability and big memory size


Illustration

OSPF is the main IGP protocol used in ASON network. The relationship of

the concept between OSPF and ASON:

OSPF ASON

Router ID---------------Node ID

DR ---------------------Activate NE

BDR--------------------Backup NE

Metric------------------Hops+ Bandwidth+ Distance+ SRLG


Questions

Why OSPF is Loop-Free?

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OTA058002 OSPF Protocol Introduction ISSUE1.00