Hcip day 6 notes

OSPF Irregular areas of

OSPF Requirements for area division ：

1、 There must be... Between areas ABR

2、 Regions must be divided according to star topology

An irregular situation ：

1、 Non backbone areas away from the backbone

2、 Discontinuous backbone

Solutions ：

（ One ）、 adopt VPN The tunnel will R4 Connect to the backbone area , Legalize it

1、 When a router connects backbone areas and multiple non backbone areas at the same time , Routing information can be directly transmitted between non backbone areas without going through the backbone .

2、 Take a stake in a router and directly learn the routing information from the region and from others at the same time ABR The same routing information learned , The router will unconditionally trust the routing information it has learned , Even if the cost is greater than others .

summary --- VPN The disadvantage of tunnel solving the problem of irregular area

1、 It may cause poor route selection

2、 It may cause repeated updates

3、 because R2 and R4 Need to build neighborhoods , therefore , It will generate data sent periodically , This leads to the waste of regional link resources .

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

[ospf Regional perspective ]vlink-peer <rid>

display ospf vlink --- View virtual link table

Virtual link has the disadvantage of solving the problem of irregular area

1、 A link establishes a virtual relationship with a neighbor , therefore , It will also send periodic data to keep alive , It will also cause a waste of resources in the crossing area

2、 Limit to only one area

3、 Multi process bidirectional republication

We republish to configure and run different protocols （ Different processes of the same protocol ） On the border router , Such a border router is called ASBR --- Autonomous system border router （ Protocol boundary router ）

[ospf process ]import-route ospf < Process number > --- Two way configuration

summary --- First , Republishing as a solution will not cause periodic data consumption of resources , There will be no poor routing and repeated updates , however , Because the imported route is recognized as an extraterritorial route , Its controllability is low , therefore , Set a lower priority .

OSPF Of LSA

LSA --- Link status notification --- OSPF The protocol is produced in different network environments , Used to carry and convey different information .

LSDB --- Link state database

OSPFV2 Version requirements must be mastered LSA There are six types

TYPE --- type --- It stands for LSA The type of

LinkState ID --- Link state identifier --- The function is to mark a LSA Information , It's equivalent to this LSA The name of .

AdvRouter --- Notify router --- Send this LSA Information router RID.

The above three parameters are called LSA A triple , Through these three parameters, we can uniquely calibrate a LSA Information .

Check a certain item LSA --- display ospf lsdb <type> <linkstate id>

LSA The content of the header

TYPE

LinkState ID

AdvRouter

Ls age --- Company S --- Aging time --- When LSA Set to... When generated by the originating router 0（ Not to join LSDB Then time it ）, after , The LSA Spread in the network ,LSA The aging time will also accumulate all the time .--- Under normal circumstances ,LSA The aging time will not exceed 1800S. --- MAX AGE --- 3600S.

SEQ --- Serial number --- Each router sends the same message LSA Will carry a serial number , also , This serial number will be added one by one 1, Is a judgment LSA New and old important parameters .

Linear sequence space --- advantage , The old and new relationship is well confirmed ; shortcoming , When the serial number space is used up, the old and new relationships cannot be compared .

Cyclic sequence space --- advantage , The serial number space can be recycled ; shortcoming , When the difference between two serial numbers is too large , It will be impossible to judge the old and new relationship

Lollipop type sequence space --- OSPF Using the lollipop sequence space , however , In order to avoid the old and new relationship cannot be judged after entering the circular space , therefore ,OSPF It is required not to enter the cycle （ It is equivalent to using linear sequence space --- The value range is equivalent to from 0X80000001 - 0X7FFFFFFE）

OSPF Method of refreshing space serial number --- When one LSA When the serial number of the message reaches the maximum , The device sends the message LSA This message will be at the same time LSA Set the aging time of as the maximum aging time --- 3600S, The neighbor received this LSA After the message , Because the serial number is the latest serial number , The local corresponding... Will be replaced LSA Information , after , And because the aging time is 3600S, Then the LSA Information deletion . The local device will send another same message LSA, And the serial number is 0X80000001, The neighbors will send the latest LSA The information is stored in the database , Refresh the serial number space .

Chksum --- The checksum --- This checksum will also participate in LSA Old and new judgments , When two LSA When the serial numbers of are the same , Compare checksums , Large checksum is new .

OSPF Periodic update of --- Every one of them LSA The aging time reaches 1800S when , Periodic updates will be made .

Group pace timer --- 300S --- When there is LSA The aging time reaches 1800S when , Periodic updates are not performed immediately , But wait 300S, When reach 2100S when , Will update all at the same time 1800S Of LSA Information .（ Optimization mechanism , Not the default ）