The most widely used dynamic routing protocol: OSPF

Hello , This is the network technology alliance station .

In the previous section, we introduced the dynamic routing RIP, What I bring to you today is OSPF.

Let's go straight to ！

[TOC]

What is? OSPF？

OSPF, English full name ：

Open Shortest Path First

, Chinese name ：

Open shortest path first

.

OSPF yes  IP  One of the series of routing protocols , yes  Internet  Of

Internal gateway protocol

 (IGP), Used in  IP  Network

A single autonomous system

 (AS)  To distribute  IP  Routing information .

OSPF It's a network layer protocol , Applicable to agreement No  89,AD  The value is  110.

OSPF  Use multicast addresses

 224.0.0.5

  Normal communication , Use  

224.0.0.6

  Update to the specified router （DR）/ Back up the specified router （BDR）.

OSPF  The term

• neighbor
  ： function  OSPF  The connection of （ adjacent ） Router , Adjacent interfaces are assigned to the same area , Neighbors are through  Hello  Packet found （ Unless manually configured ）.

• Adjacency
  ： Router and its corresponding  DR  and  BDR  Logical connection between , Unless adjacency is formed , Otherwise, the routing information will not be exchanged .

• LSA
  ：  Link status notification , The packet contains link status and routing information , stay  OSPF  Shared between neighbors .

• DR
  ： Specify router ,

• BDR
  ：BDR  It is in the broadcast network  DR  Backup of . When  DR  outage ,BDR  Turn into  DR  And perform its functions .

• Area
  ： Zones are used to establish hierarchical networks .

• ABR
  ： Area border router .

• ASBR
  ： Autonomous system border router .

• NBMA
  ： Non broadcast multiple access .

• Router-ID
  ： Used to identify  OSPF  The router  IP  Address .

• Link state
  ： Link status between two routers .

• cost
  ： Link state protocol assigns a value called cost to each link .

OSPF  characteristic

• Classless routing protocol

• Support VLSM、CIDR、 Manual route summary 、 Equivalent load balancing

• Support incremental updates

• Use only one parameter as the metric ： Interface costs .

• OSPF  The management distance of the route is... By default  
  110
  .

• Use multicast addresses  
  224.0.0.5
    and  
  224.0.0.6
    Make route updates .

OSPF  Message type

OSPF  Altogether 5 Two message types ：

Hello message

Also known as Type-1 Data packets , There are two uses ：

• The neighbors found out

• Keep Alive

stay 224.0.0.5 Multicast on .

DD message

DD, English full name ：

Database Description

, Chinese meaning ：

Database description

.

Used to synchronize between two routers LSDB （

Link state database

）.

LSR message

LSR, English full name ：

Link State Request

, Chinese meaning ：

Link status request

.

For from  OSPF  Neighbor routers request specific link state records .

LSU message

LSU, English full name ：

Link State Update

, Chinese meaning ：

Link status update

.

Yes  LSR（ Link status request ） Reply to .

LSAck message

LSAck, English full name ：

Link State Acknowledgement

, Chinese meaning ：

Link status confirmation

.

For confirmation purposes LSR, The receiving end can be checked  OSPF  Whether the router successfully received  LSU.

LSA type

OSPF  Altogether 7 Kind of LSA type ：

Router-LSA

LSA 1  Class is

The most basic

Of  LSA, from

all

 OSPF  Router generation , Generated LSA 1 All flooding in the area ,LSA 1  Contains all the  OSPF  Router link information , Include the link type of the neighbor 、 expenses 、IP Address and router ID.

Pictured ,Type 1 LSA Only in Area 0  That is, communication within the same area , In different areas Type 1 LSA Is different .

Network-LSA

LSA 2  class   The Internet  LSA  from  

DR

  Generate on each multi access network ,DR  Represent

multiple

A router that accesses the network , The Internet  LSA  Shows the multiple access network  OSPF  Router connection , contain DR Of IP Address 、 List of routers connected to the multi access network and subnet mask of the multi access network ,DR  Generated network  LSA  It will flood all networks in the area .

Pictured , In area Area0 in , There are multiple channels , here Type 2 LSA from DR issue .

Network-summary-LSA

LSA 3  Class by  ABR（ Area border router ） Generate , It is used to announce the network of one area to other areas .

Pictured ,R2 yes ABR,ABR Generate Type 3 LSA, Put the area 1 Of Type 1 LSA Inform to area 0  and  area 2.

ASBR-summary-LSA

LSA 4  Class by  ABR（ Area border router ） Generate , It is used to inform its area how to arrive  ASBR（ Autonomous system border router ）.

Pictured ,R1 Connected to other protocols RIP Network of , therefore R1 by ASBR,R1  adopt  Type 1 LSA Pass your routing information to R2,R2 yes ABR, Will generate Type 4 LSA, Tell other areas how to get there  ASBR namely R1.

AS-external-LSA

LSA 5  Class by  

ASBR

  Generate , Right and wrong OSPF  The routing information of the device , Generally speaking , In large networks , There are a large number of these in the router's database LSA.

Pictured ,RIP Right and wrong of the agreement OSPF agreement , Now? RIP Network is 192.168.1.0/24, This time in order to 192.168.1.0/24 Published in the OSPF In the area ,ASBR R1 Will generate Type 5 LSA, Then notify other areas .

NSSA LSA

LSA 7  Class by  NSSA  Medium  

ASBR

  Generate ,NSSA  Medium  ASBR  Will not  OSPF  The network address information of the domain is flooded to  NSSA  in , because  NSSA  external  LSA  Only in  NSSA  Internal flooding , therefore  NSSA ABR  take  LSA  type  7  Convert to  LSA  type  5  And announce it to the backbone area .

Opaque LSA

• 9  class  LSA Only in the release  LSA  The network segment where the interface of is located is published .

• 10  class  LSA stay  OSPF  Publish in the area .

• 11  class  LSA stay  AS  Internal release

Router type

OSPF  Altogether  4  There are two types of routers ：

IA

IA  English full name ：Internal Router, It means ： Regional routers .

All interfaces of routers in the area are in the same area , All IntrAzone routers in a zone have the same  LSDB.

Pictured ,R1、R2、R6、R7 All are IA.

BR

BR  English full name ：Backbone Router, It means ： Backbone router .

The backbone router is the router in the backbone area , The backbone areas are all areas  0.

Pictured ,R3、R4、R5 All are BR.

ABR

ABR  English full name ：Area Border Router, It means ： Area border router .

Located in one or more  OSPF  The routers that border areas and connect these areas to the backbone network are called  ABR.

ABR  Connect to multiple  OSPF  Area , Therefore, there can be multiple in a network  ABR, therefore ,ABR  Yes

Multiple

Link state database instance ,ABR  There is a database for each region , The database has been summarized , Then submit to the trunk , For distribution to other areas .

Pictured ,R3 and R5 Namely ABR.

ASBR

ASBR  English full name ：AS Boundary Router, It means ： Autonomous system border router .

ASBR  Is located in the use of  OSPF  A network that performs routing （OSPF  Domain ） And execution of non  OSPF  Routed network （ For example, static routing 、RIP/EIGRP/BGP（ Not  OSPF  Domain ）） The border between the routers .

ASBR  Is configured from non  OSPF  The routing process is reassigned to  OSPF  The router , Because communication is two-way , therefore  ASBR  Also need to  OSPF  Routes are redistributed to non  OSPF  Domain .

Pictured ,R5 Namely ASBR.

Routing type

OSPF  Altogether  4  Routing types ：

Intra Area

Intra Area, That is, intra region routing , As shown in the figure below ：

R2 take 192.168.1.0/24 Declare as an IntrAzone route , It is a route within the same region .

Inter Area

Inter Area It is inter region routing , As shown in the figure below ：

R3 stay area1 Declare 192.168.2.0/24, Make it an interregional route .

Type1 External

Type1 External, This is the first type of external routing , Equivalent to link state metrics , The cost is equal to the sum of internal cost and external cost ,

high reliability

.

Type2 External

Type2 External, This is the second type of external routing , Greater than  AS  The cost of any internal path , The cost is equal to from ASBR  The cost of routing to the destination ,

Low reliability

.

Area type

OSPF  Altogether  5  Area types ：

Common areas

Common areas include standard areas and backbone areas .

area0 It's the backbone area , yes  OSPF  Online

center

, As shown in the figure , All other areas are connected to these backbone areas

Connect to area0 All areas are standard areas , Here's the picture ,area1 and area2 They are all standard areas .

STUB Area

STUB Area is the first specific area , Belonging to an external autonomous system is not acceptable （AS） The routing , They are usually used to reduce  LSA  flooding 、LSDB  And routing table size . therefore , This type of area is used where there is a little sensitivity to high traffic .

Totally STUB Area

Totally STUB The region does not allow routes outside the region and default routes to propagate within the region ,ABR  Inject the default route into the area , All routers belonging to the zone use the default route to send any traffic outside the zone .

NSSA Area

NSSA  representative  not-so-stubby area, allow  OSPF Stub  Zones carry external routes , These routes are from  RIP、EIGRP  or  BGP  And other protocols , Then reassign to  NSSA  The zone will create a special type of link state notification  (LSA), Called type  7, It can only exist in  NSSA  Area .

Totally NSSA Area

Totally NSSA Regional and  NSSA  Areas are similar , But external and inter region routing is from the region  0  It will be filtered , A default route will be posted to it .

Network type

OSPF The following network types are supported ：

The radio type

• The broadcast type is OSPF Default network type

• The link is required to support the  2  Layer broadcast function

• Need to use  DR/BDR

Complete... For broadcast network  DR  and  BDR  choice .

NBMA type

• OSPF Frame relay default network type

• Each neighbor is connected to each other by unicast , And all  OSPF  Packets are unicast

• Need to use  DR/BDR

Point to point P2P type

• Do not maintain  DR/BDR  Relationship

• Used between two routers

Point to point P2MP type

• Don't keep  DR/BDR  Relationship

• Through multicast address 224.0.0.5 send out hello package

• It is used to force traffic from multiple sites to pass through the headquarters or central location

summary

OSPF It is one of the most important technologies in data communication technology , Today, Rego spent a lot of time explaining , This article cost 3 Days time , I wrote it in my spare time every day , I hope it can help you ！