zte ospf protocol, principle and configuration

OSPF Routing Protocol Principle

V2.1

Outline

Through learning this course, you will: Master computing methods of OSPF routing

protocol Master advanced applications of OSPF routing

protocol

Contents

OSPF Overview OSPF Concept OSPF Working Process Area Allocation LSA Transmission among Multiple Areas Route Optimization

OSPF Overview

Open Shortest Path First (OSPF) OSPF is Internal Gateway Protocol (IGP).

OSPF is a kind of link-state protocol, it maintains complex network topology database and then adopts SPF algorithm to calculate the best route.

The types of network supported by OSPF are classified into multi-access network and point-to-point network.

OSPF Advantages

No route loop Adapt to large-scale network High convergence rate of route Support area allocation Support equivalent route Support verification Support hierarchic management Transmit protocol messages in multicast address

Contents


Hi, I am router A and my name is 192.132.1.3.

OSPF Concept (1)

Router ID Definition: 32-bit binary to identify each router on OSPF network. Selection method: SelecteThe IP address of the interface which is activated firstly. If

multiple interfaces are activated, the minimum IP address of the router is selected on the ZTE router.

If loopback interface is configured on the router, router ID will be the minimum IP address of all loopback interfaces, in spite of IP addresses of other physical interfaces or even when they are activated.

Features: Globally unique; Once selected, it cannot be changed unless OSPF progress is

restarted. ZXR10# clear ip ospf process <process-id>

OSPF Concept (2) Interface Interfaces run OSPF protocol; transmit protocol messages periodically (Hello packet) to search and find

neighbors. Designated Router (DR) and Backup Designated Router (BDR) To reduce traffic of OSPF synchronous link state information, broadcast

network can be automatically represented as DR or BDR according to interface priority or router-id.

Link State Database Contains link state of all routers on the network and indicates the topology

structure of the whole network. Neighboring Routers OSPF routers on the direct network become neighbors automatically after

exchanging hello packets. Adjacency On the basis of neighbors, Link State Advertisement (LSA) is synchronized to

form adjacency.

OSPF Working Process (1)

Run OSPF protocol and find neighbors;

Exchange LSA, synchronize Link State Database (LSDB), and form adjacency;

Use SPF algorithm to establish the shortest path tree and calculate the best route.

OSPF Working Process (2)

Autonomous system

Route tableTopology databaseNeighbor table

Interfaces start OSPF

Contents

OSPF Overview OSPF Concept OSPF Working Process Finding Neighbors Selecting DR or BDR Forming Adjacency Updating LSA Computing Optimal Route Area Allocation LSA Transmission among Multiple Areas Route Optimization

Neighborhood

Hello

afadjfjorqpoeru39547439070713

Router IDHello/dead intervalsNeighborsArea-IDRouter priorityDR IP addressBDR IP addressAuthentication passwordStub area flag

* *

* *

Hello

A

D E

CB

Interfaces run OSPF send periodicallyItems with *which must be consistent to establish neighbors

Neighborhood—Hello Message

Process of Forming OSPF Neighbor List

10.75.32.1/30Int1

10.75.32.2/30Int1A B

Lo: 10.75.0.1 Lo: 10.75.0.2

RB Neighbors List RA Neighbors List

Hello, my router ID is 10.75.0.1 and see no neighbors.

Down State

10.75.0.1, int1 , init

Hello, my router ID is 10.75.0.2 and my neighbor is 10.75.0.1.

Init State

10.75.0.2, int1 , 2-way

Hello, my router ID is 10.75.0.1 and my neighbor is 10.75.0.2.

Two-way

10.75.0.1, int1, 2-way

Contents


LSA Synchronization on Broadcast Network

On broadcast network or NBMA, resource will be wasted when each neighbor transmits LSA (network bandwidth and CPU resources).

Neighbor, receive my LSA.

Functions of DR and BDR

To reduce traffic of OSPF protocol messages, each network segment uses DR or BDR to represent the network.

Each router can synchronize LSA with DR and BDR to form adjacency.

DR BDR

P=1 P=0P=1

Selection of DR and BDR

P=3 P=2

Hello

DR BDR

The router that is started first on the network is selected as DR; When started simultaneously or reselected, the router with the

superior priority (0-255) is selected as DR; When started simultaneously or with the same priority, the router

with the largest ID is selected as DR; DR selection is not preemptive unless OSPF progress is restarted.

Selection of DR and BDR—Hello Message

Contents


Forming Adjacency of OSPF (1)

10.75.32.1/30Int1

10.75.32.2/30Int1A B

Lo: 10.75.0.1 Lo: 10.75.0.2

RB Neighbors List RA Neighbors List

DR, I will initiate interaction of LSA and I am the master sender (MS=1).

10.75.0.1, int1 , init10.75.0.2, int1 , 2-way 10.75.0.1, int1, 2-way

DR

Exstart

10.75.0.2, int1, Exstart

DBD


No, I am the master sender, because I have higher router ID. DBDafadjfjorqpoeru39547439070713

10.75.0.1, int1, Exchange

This is summary information about my LSDB. DBD

afadjfjorqpoeru39547439070713Exchange State

This is summary information about my LSDB.DBD


10.75.0.2, int1, Exchange

Forming Adjacency of OSPF (2)

10.75.32.1/30Int1

10.75.32.2/30Int1A B

lo ： 10.75.0.1 lo ： 10.75.0.2

RB Neighbors List

10.75.0.1, int1 , init10.75.0.1, int1, Exchange

DR

I have no information about 172.16.6.0/24 and I need entire LSA.LSR


Loading State

This is LSA of 172.16.6.0/24. LSU


RA Neighbors List

10.75.0.1, int1 , init10.75.0.2, int1, Exchange10.75.0.2, int1, Loading

Full State

Received, thanks!LSAck


10.75.0.2, int1, Full

My LSDB is complete. No query is needed.

10.75.0.1, int1, Full

Contents


Flooding Process (1)

The router notifies changed topology information of neighbors in 224.0.0.5.

xx

Point-to-point link state changes

LSU1

LSU

Update route table

2

3

A B

Update route table4

LSU

3

LSU

2

xxLSU1

Flooding Process (2)

Router A notifies DR in 224.0.0.6. DR notifies other routers in 224.0.0.5.

Broadcast link state changes

DR

A B

Contents


Process of Computing OSPF Protocol

LSDB

LSA of RTA

LSA of RTB

LSA of RTC

LSA of RTD

(2) LSDB of each router (3) Weighted digraph created by 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

RTA

RTC

RTD

3

2

1

5

(1) Network topology structure

(4) Each router computes the minimal spanning tree with itself as the root node.

RTB

Computing Minimal Spanning Tree

Sum of COST from external ports in data forwarding direction

Cost=1

Cost=5

Cost=1

Cost=5

10.1.1.0/24 10.2.2.0/24 10.3.3.0/24

Ospf route TableNet Cost10.2.2.0 210.3.3.0 3

Ospf route TableNet Cost10.1.1.0 10

A B C

Cost=1

Contents


Problems Large-Scale OSPF Network Meets

My route table is too large and my memory is too small.

Always computing route table, boring!

Only LSA is received, no data.

OSPF OSPF

OSPF

OSPF

OSPF

Area 0

Area 1 Area 2

Autonomous system

Solution: Allocate Areas

Rules for allocating areas: Each network segment must belong to an area, that is, each interface that runs OSPF protocol must

be designated to an area; Each area is identified by area ID, which is an integer ranging from 0 to 32; Backbone area (area 0) cannot be separated by non-backbone areas; Non-backbone areas (not area 0) must be connected to backbone area (virtual link is not

suggested).

Advantages for Allocating Areas

Only LSDB of routers in the same area can be synchronized. The changes of network topology structure are first updated within the area..

After areas are allocated, route aggregation can be performed on the boundary router within the area to reduce the number of LSA notified to other areas and minimize the influence caused by changes of network topology.

External AS

Internal router

Backbone/internal router

ABR and backbone router

ABR and backbone router

Internal router

ASBR and backbone router

Area 1 Area 2Backbone area 0

Types of OSPF Routers

Contents


Types of LSA

Types of LSA Initiator Transmission Range Described Object

LSA1:Router LSA

Each router in the area

Within the area Direct link state of the router

LSA2:Network LSA

DR and BDR Within the area Directly connected routers within the network segment

LSA3:Network Summary LSA

ABR Among areas Route of the area where ABR is located (LSA1 and LSA2)

LSA4:ASBR Summary LSA

ABR Among areas Notify ASBR of the area where ABR is located

LSA5:Autonomous system external LSA

ASBR Among areas Notify exterior route (non-ospf route, such as RIP or BGP)

Types of LSA

Router

Area 1 Area 0

Network

Summary

External

ExternalAS

DR

ABR ASBR

Flooding of LSA among Multiple Area Network

Type 1


Area 1 Area 0 Area 50

Type 3


Type 3


RIP

Internal ABR1 ABR2 Internal

BBone

Type 5


Type 5

afadjfjorqpoeru39547439070713afadjfjorqpoeru39547439070713

Type 4


Contents

OSPF Overview OSPF Concept OSPF Working Process Area Allocation LSA Transmission among Multiple Areas Route Optimization Stub Area Route Summarization

Constitution of OSPF Route

Route table

Route among areas

Route within areas

External route (non-OSPF route)

Area 1

Area 1 Area 0

Area 1 RIP

Totally Stubby

Do not receive route outside areas Network Summary LSADo not receive redistributed routeASBR Summary LSAAutonomous system external LSA

Do not receive redistributed routeASBR Summary LSAAutonomous system external LSA

Area 0

Receive all LSA

Types of Areas

Stub

Stub and Totally Stubby Area (1)

Area 1Area 0Area 50RIP

C D A B E F

ABR ABR

ASBR

1.1.1.0 1.1.2.0 1.1.3.0

2.1.1.0

2.1.2.03.1.1.0

3.1.2.0

4.1.1.04.1.2.0

1.1.1.0 int1 ospf1.1.2.0 int1 ospf1.1.3.0 int1 ospf

2.1.1.0 int1 direct2.1.2.0 int2 direct3.1.1.0 int1 ospf3.1.2.0 int1 ospf4.1.1.0 int1 ospf4.1.2.0 int1 ospf

1.1.1.0 int1 direct1.1.2.0 int1 ospf1.1.3.0 int1 ospf2.1.1.0 int2 direct2.1.2.0 int2 ospf3.1.1.0 int1 ospf3.1.2.0 int1 ospf4.1.1.0 int1 ospf4.1.2.0 int1 ospf

RD route tableRC route table

1.1.1.0 int1 ospf1.1.2.0 int1 ospf

1.1.3.0 int1 direct2.1.1.0 int1 ospf2.1.2.0 int1 ospf

3.1.1.0 int2 direct3.1.2.0 int2 ospf4.1.1.0 int1 ospf4.1.2.0 int1 ospf

RE route table

1.1.1.0 int1 ospf1.1.2.0 int1 ospf1.1.3.0 int1 ospf2.1.1.0 int1 ospf2.1.2.0 int1 ospf

3.1.1.0 int1 direct3.1.2.0 int2 direct 4.1.1.0 int1 ospf4.1.2.0 int1 ospf

RF route table

Default

Default

Summary

Default


Area 1—Totally StubbyArea 0Area 50—Stub

Summary

External External

RIP








Internal ABR1 ASBR BBone ABR2 Internal

Summary



Area 1—Totally StubbyArea 0Area 50—StubRIP

C D A B E F

ABR ABR

ASBR

1.1.1.0 1.1.2.0 1.1.3.0

2.1.1.0

2.1.2.03.1.1.0

3.1.2.0

4.1.1.04.1.2.0

1.1.1.0 int1 ospf1.1.2.0 int1 ospf1.1.3.0 int1 ospf

2.1.1.0 int1 direct2.1.2.0 int2 direct3.1.1.0 int1 ospf3.1.2.0 int1 ospf0.0.0.0 int1 ospf

1.1.1.0 int1 direct1.1.2.0 int1 ospf1.1.3.0 int1 ospf2.1.1.0 int2 direct2.1.2.0 int2 ospf3.1.1.0 int1 ospf3.1.2.0 int1 ospf4.1.1.0 int1 ospf4.1.2.0 int1 ospf

RD route tableRC route table

1.1.1.0 int1 ospf1.1.2.0 int1 ospf

1.1.3.0 int1 direct2.1.1.0 int1 ospf2.1.2.0 int1 ospf

3.1.1.0 int2 direct3.1.2.0 int2 ospf4.1.1.0 int1 ospf4.1.2.0 int1 ospf

RE route table

3.1.1.0 int1 direct3.1.2.0 int2 direct 0.0.0.0 int1 ospf

RF route table

Only one outletNo ASBR within the areaCan not be AREA 0 (Backbone)No Virtual links

Limitation of Stub and Totally Stubby Area

Unique outlet

Area 20.0.0.0

ExternalAS

0.0.0.0

R3 R4

XX

NSSA

Not So Stubby Area

To Other Area Type 5

Area 2

ExternalAS

RIP

Type 7Type 7

Area 0

R3R4

Contents

OSPF Overview OSPF Concept OSPF Working Process Area Allocation LSA Transmission among Multiple Areas Route Optimization Stub Area Route Summarization

Reduce the size of route table Limit the influence of topology changes in the local area Reduce the number of LSAs and save CPU resource

Support Route Summarization

Area 0 backbone area

ABRs

Area 1

Summarized route

xx

A summarized route can represent multiple sub networks.

Route Summarization

O 172.16.8.0 255.255.252.0O 172.16.12.0 255.255.252.0O 172.16.16.0 255.255.252.0O 172.16.20.0 255.255.252.0O 172.16.24.0 255.255.252.0O 172.16.28.0 255.255.252.0

Route table of router B LSAs transmitted to route C

IA 172.16.16.0 255.255.240.0

Summarized route

IA 172.16.8.0 255.255.248.0

Area 1 Area 0ABR

A B C

Review

OSPF concept and features OSPF working principle OSPF area allocation Stub and Totally Stubby area Route summarization

Questions

Can OSPF achieve load balance or equivalent load balance?

How is OSPF Metric computed? How many types of LSA does OSPF have? Who

creates theses types? Can you describe the working process of OSPF?

zte ospf protocol, principle and configuration

Documents