[OSPF routing calculation (class I LSA router, class II LSA network, and class III LSA sum net)] -20211228-30

Catalog

One 、ospf Link status data

Two 、LSA The head of

​Type、LS id、Adv rtr These three attributes , It's a unique sign LSA​

LS age、seq、chksum These three attributes , It only means one LSA New and old

3、 ... and 、LSA The type of

【 A class LSA 】

1.Router

2.1 class LSA The link type of

 3.1 class LSA Complete message

4. 1 class LSA Peculiar flag Field

Used to describe whether it is a special router

 5.1 class LSA Update and undo

【 Two category LSA 】

1.network

 2. Two category LSA Update and undo

1） to update 、 The process of revoking

2）2 class LSA Updated and revoked messages  （ difference ）

 【 Three types of LSA 】

1. Interregional ABR

2. sum-net Three types of routes

【1】3 class LSA The transformation of

【2】3 class LSA to update 、 revoke  

​  Three types of updates can be found , The values of other fields have not changed , only LS Age Aging time is determined by 3600s Turn into 1s

【3】3 class LSA Inter regional flooding  

  【4】3 class LSA My guard ring

​

1.AR3 Of 3.3.3.3 A class LSA Through AR2 Turn into 3 class LSA Flood to AR1, Empathy ,AR5 It will also flood .

3 class LSA There is an anti ring rule ,1 class 、2 Class LSA be better than 3 class LSA.

3 class LSA There is an anti ring rule , really ABR You won't use non backbone areas to learn 3 class LSA.（lsdb There will be non backbone areas in the 3 Class route , But it doesn't count 、 No flooding from non backbone areas 3 class LSA）

reflection  

according to 3 class LSA Thinking about anti ring rules ,4.4.4.4 visit 3.3.3.3 The path of , and 3.3.3.3 visit 4.4.4.4 What is the path of ？？？

so 4.4.4.4 visit 3.3.3.3 The best route for 4213

so 4.4.4.4 visit 3.3.3.3 The best route for 324

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One 、ospf Link status data

Two 、LSA The head of

（ These attributes , No matter what kind LSA There are ）

Type、LS id、Adv rtr These three attributes , It's a unique sign LSA

LS age、seq、chksum These three attributes , It only means one LSA New and old

3、 ... and 、LSA The type of

【 A class LSA 】

1.Router

2.1 class LSA The link type of （4 Kind of ）

 3.1 class LSA Complete message

4. 1 class LSA Peculiar flag Field

Used to describe whether it is a special router

 5.1 class LSA Update and undo

 1 class LSA The revocation of , What is revoked is the routing information , Not the whole thing 1 class LSA, The topology information still exists , It has not been revoked .

Topology information cannot be undone , Routing information can be revoked .

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【 Two category LSA 】

1.network

 

 

 2. Two category LSA Update and undo

1） to update 、 The process of revoking

  Within this broadcast domain ,AR3 by DR, that DR Will send a class II message LSA;

1. When you disconnect DR Link to , This is class II LSA It will not disappear immediately , Also because AR3 Of down fall , There will be another election in the broadcast domain DR, So new DR-AR2 Will send a new class II LSA Information , At this time, there will be two classes II in the broadcast domain LSA.-- Updated a new category II LSA

2. When connected again AR3 Link to , because ospf Of DR Not preemptive ,AR3 Won't take over AR2 Of DR;

However, due to the two classes in the broadcast domain LSA, One of them is AR3 Self generated , And now AR3 It is no longer DR, here AR3 It will automatically cancel the second class message it has sent LSA.-- Undo your own second class LSA

It also shows ,, The meaning of this sentence .

2）2 class LSA Updated and revoked messages  （ difference ）

update ：

  When revoked ：

ospf Type of area

ospf The role of zoning

 

ospf Regional division rules ： 

 

 【 Three types of LSA 】

1. Interregional ABR

2. sum-net Three types of routes

 

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【1】3 class LSA The transformation of

It's through 1 Class （subnet） Routing information and 2 class LSA The conversion

  for example ,AR3 No announcement 3.3.3.3/32 When switching back to the route , At this time, the router generates 1 Class routing does not carry subnet Routing information , Therefore, we should 1 Class route will not be converted to 3 Class route .

        After the announcement ,1 Class produces stubnet Routing information for ,ABR Router （AR2） You can put the 1 Class route is converted to 3 Class route

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【2】3 class LSA to update 、 revoke  

When we will 3.3.3.3 revoke （undo network 3.3.3.3/32）

  Three types of updates can be found , The values of other fields have not changed , only LS Age Aging time is determined by 3600s Turn into 1s

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【3】3 class LSA Inter regional flooding  

AR2 The ABR take 3.3.3.3/32 One kind of subnet The routing information is transformed into three types LSA, here ADV router Change to own RID 2.2.2.2, When AR2 Flood water supply area2 yes AR3, Received this 3.3.3.3 Of 3 class LSA, Empathy , take ADV router Change to own RID 1.1.1.1.

（ Equivalent to , I ABR What I receive belongs to me , So the received route is my last name , That is to modify ADV router For their own RID）

  【4】3 class LSA My guard ring

1.AR3 Of 3.3.3.3 A class LSA Through AR2 Turn into 3 class LSA Flood to AR1, Empathy ,AR5 It will also flood .

here lsdb There will be two in the database 3.3.3.3 Three categories of LSA, here AR5 There are both area1 Medium 3.3.3.3 A kind of routing , There are also from AR2 Flooding 3.3.3.3 Three categories of LSA, At this point, which one should be selected for communication ？？

The answer is ：

3 class LSA There is an anti ring rule ,1 class 、2 Class LSA be better than 3 class LSA.

so , here AR5 Will choose from area1 Medium 3.3.3.3 A kind of routing .

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2.AR4 stay area2, here 4.4.4.4 Of 1 class LSA Through AR2 Turn into 3 class LSA Flood to AR2、AR5, here AR5 Will it flood to AR1？？？ Can't

AR5 Learned that 3 class LSA（4.4.4.4/32）, It has access to 4.4.4.4/32 Do you ？？？ You can't

  The answer is ：

3 class LSA There is an anti ring rule , really ABR You won't use non backbone areas to learn 3 class LSA.（lsdb There will be non backbone areas in the 3 Class route , But it doesn't count 、 No flooding from non backbone areas 3 class LSA）

  here ,AR5 What I learned is from area2 Of 3 Class route , Therefore, it will not flood to AR1, But at this time AR5 Of lsdb The database has this 3 class LSA Of , Just do not calculate and flood , To keep the database synchronized .

And even if you learn how to 3 class LSA, Even if lsdb There is the 3 class LSA, Will not visit 4.4.4.4, because 4.4.4.4 It is from the non backbone area 3 class LSA,ABR This route will not be calculated at all 、 I can't use .

 

• reflection  

according to 3 class LSA Thinking about anti ring rules ,4.4.4.4 visit 3.3.3.3 The path of , and 3.3.3.3 visit 4.4.4.4 What is the path of ？？？

1. When 4.4.4.4 visit 3.3.3.3 when

  You need to know first 3.3.3.3 The routing ,AR2 take 3.3.3.3 Of 1 class LSA Convert to 3 class LSA Red to area 0 and area 2. here , Received two messages that are both 3 Class LSA, Compare the expenses ,ABR To the destination address 3.3.3.3 The cost is 1, Local 4.4.4.4 To ABR There are two costs of （ Walk on the road and pass AR1 The cost is 2, Go down the road p2p The cost is 48）, So the cost is small ,2+1=3,

so 4.4.4.4 visit 3.3.3.3 The best route for 4213

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2. When 3.3.3.3 visit 4.4.4.4 when

  Empathy , You need to know first 4.4.4.4 The routing ,AR1 take 4.4.4.4 Of 1 class LSA Convert to 3 class LSA after AR2 Red to area 1; Another kind ,AR2 from 4.4.4.4 Learned 1 class LSA Direct reddening to area 1 .

here , Received two different types of LSA, One is a kind of , One is of three categories , according to 3 class LSA Anti ring principle of , Class I, class II LSA be better than 3 class LSA, So the cost value is not compared , Directly in LSA In terms of type, I chose to go down the road

so 4.4.4.4 visit 3.3.3.3 The best route for 324

 ospf Routes are compared first LSA The type of ,1 class 2 class LSA Prior to the 3 class , if LSA If the type is the same, compare the cost , Low cost priority .