ota058002 ospf protocol introduction issue1.00
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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
HUAWEI TECHNOLOGIES CO., LTD. Page 3All rights reserved
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
HUAWEI TECHNOLOGIES CO., LTD. Page 4All rights reserved
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.
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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
HUAWEI TECHNOLOGIES CO., LTD. Page 6All rights reserved
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
HUAWEI TECHNOLOGIES CO., LTD. Page 7All rights reserved
Chapter 1 Basis of OSPF protocolChapter 1 Basis of OSPF protocol
Chapter 2 OSPF routing calculation methodChapter 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
HUAWEI TECHNOLOGIES CO., LTD. Page 8All rights reserved
Network Topology
Network topology is described by OSPF through the link status
FR/X.25
EthernetEthernet
PPP
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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
HUAWEI TECHNOLOGIES CO., LTD. Page 10All rights reserved
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
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Neighbor State Machine
Down
Attempt Init
2-way ExStart Exchange
Loading
Full
HUAWEI TECHNOLOGIES CO., LTD. Page 12All rights reserved
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
HUAWEI TECHNOLOGIES CO., LTD. Page 13All rights reserved
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
HUAWEI TECHNOLOGIES CO., LTD. Page 14All rights reserved
DR Vote
A B C
D E
Network Topology
A
ED
CB
(DR)A
ED
CB
Adjacency Relationship without DR Adjacency Relationship with DR
HUAWEI TECHNOLOGIES CO., LTD. Page 15All rights reserved
Route
M= n(n-1)/2 = 28
M= (n-2)×2+1 = 13
DR
BDR
Routes without DR Routes with DR
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NBMA and Point-to-Multipoint
NBMA: Full meshed Point-to-Multipoint: Partial meshed
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Network Types
Broadcasting ( Ethernet )
NBMA( Frame Relay, X.25 )
Point-to-Multipoint( Frame Relay, X.25)
Point-to-Point (PPP)
HUAWEI TECHNOLOGIES CO., LTD. Page 18All rights reserved
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
HUAWEI TECHNOLOGIES CO., LTD. Page 19All rights reserved
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.
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Area Division
Area0
Area1 Area3
If the network is too big, we need to divide it into several areas.
HUAWEI TECHNOLOGIES CO., LTD. Page 21All rights reserved
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.
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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
HUAWEI TECHNOLOGIES CO., LTD. Page 23All rights reserved
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
HUAWEI TECHNOLOGIES CO., LTD. Page 24All rights reserved
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
HUAWEI TECHNOLOGIES CO., LTD. Page 25All rights reserved
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
HUAWEI TECHNOLOGIES CO., LTD. Page 26All rights reserved
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
HUAWEI TECHNOLOGIES CO., LTD. Page 27All rights reserved
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
HUAWEI TECHNOLOGIES CO., LTD. Page 28All rights reserved
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
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