Notes on the sixth day

ospf Irregular area division requirements

1、 There must be... Between areas ABR equipment

2、 Regions must be divided according to star topology

1、 Non backbone areas away from the backbone

2、 Discontinuous backbone

 

Information isolation （R4 illegal ABR）

One 、 By using VPN Tunnel makes illegal ABR legal

Some routes are poorly selected --- reason ： There are different ways to obtain topology information

Be careful ：

R4 Creating a virtual private line （ Tunnel ） after , Regions can be learned directly from topology information 0 Routing information for , At the same time, you can also go through R2 Put the area 0 Topology information

shortcoming ：

1、 Because of the existence of tunnels , There may be poor route selection , This leads to additional encapsulation of data, which wastes resources .

2、 It could be a waste of resources .

3、 Because of the existence of virtual links , Lead to R4 and R2 We need to establish a neighbor relationship , As a result R2 and R4 The periodic data between them must pass through the middle area 1, This leads to a waste of resources in the middle area .

Two 、 Use OSPF Virtual link solves the problem of irregular area

[R4-ospf-1-area-0.0.0.1]vlink-peer 2.2.2.2

The virtual link configuration is bidirectional

Only one area can be crossed

Always belong to the area 0

  shortcoming

1、 Because of the existence of virtual links , Lead to R4 and R2 We need to establish a neighbor relationship , As a result R2 and R4 The periodic data between them must pass through the middle area 1, This leads to a waste of resources in the middle area .

2、 Only one area can be crossed

3、 Multi process bidirectional republication

ASBR-- Self made system boundary routing （ Protocol boundary router ）

Redistributions need to run on border routers running different protocols at the same time ,OSPF Such a border router is called ASBR--- Only after the republishing action is executed can the republishing action be realized, and the device after the republishing action can be called ASBR equipment .

[r4-ospf-2]import-route ospf 1

shortcoming

The imported routing information flag is ---O_ASE

O_ASE--- It is recognized as extraterritorial routing information --- The controllability of such routing information is poor

seq#--- Serial number

Serial number ---32 Bit binary structure , from 8 position 16 Base to represent --- A router , Every time you send the same LSA Information , Will carry a serial number , And the serial number is added in turn 1.

Serial number space

1、 Linear sequence space --- The value starts from the minimum value to the maximum value , One time plus 1

advantage ： Old and new relationships are easy to judge

shortcoming ： length （ Number ） Co., LTD. . If the upper limit is exceeded , Then no serial number will be available , The old and new relationship cannot be judged .

2、 Cyclic sequence space --- The value starts from the minimum value to the maximum value , One time plus 1.

The purpose of emergence --- Solve a limited number of problems

advantage ： Serial number can be recycled , The serial number will not be used up

shortcoming ： When the difference is large, it is difficult to judge the old and new relationship

3、 Lollipop type sequence space ---OSPF This sequence space is used

shortcoming ： After entering the circulation part , We will still face the problem of cyclic sequence space

Type - 1LsA ---  All devices in the network will send , And only send one class LsA.  A class LsA Of Ls lD The value is equal to that of the notifier RlD.

L1NK ---  Parameters used to describe the connection of router interface , One interface can use more than one Link To describe .

Linktype ---  This type is mainly related to the network type of the interface , He will judge what kind of network the interface is running in according to the network type of the interface .

Type-2LsA --- stay MA In the Internet , Rely solely on 1 class LsA Information description may appear Incomplete situation , therefore , Need to pass through 2 class LsA Supplement the missing information . --- because 2 class LsA All the information provided is public information , therefore , You don't need to send all the equipment ,  In a MA In the Internet , Just need a device to send it .

All that carry routing information LsA All need to pass 1 Classes and 2 class LsA Check calculation .   ---- So-called Checking means that the location information of the notifier who transmits the routing information needs to pass 1 class ,2 class LsA The information is calculated .

Type-3LsA --- It transmits inter domain routing information , It mainly carries the information of the target network segment and Cost value . The target network segment information passes Ls1D To carry , It will also contain its mask letter Rest . The cost value refers to the cost value of the advertiser reaching the target network segment .