Hcip --- OSPF details

OSPF Of Irregular area division Of requirement ：

1, There must be... Between areas There is ABR equipment

2, The division of areas must be in accordance with Star topology division .

1, Non backbone areas away from the backbone

2, Discontinuous backbone

 

1. Use VPN Tunnel send Illegal ABR Legalization

In the process , One thing you can notice , Namely R4 stay Create a virtual private line after , Sure straight

Then learn through topology information To the region 0 Routing information for , At the same time, you can also go through R2 Put the area 0 

The routing information of is sent to R4, and R4 Meeting Unconditional trust Routing letter from topology

Rest , Even if the cost value is very large .

Use VPN Tunnels solve irregular areas Of shortcoming ：

1, Because of the existence of tunnels , May appear Poor route selection The situation of , Cause extra data

encapsulation , Waste resources .

2, There may be Repeat updates The situation of

3, Because of the existence of virtual links ,AR4 and AR2 We need to establish a neighbor relationship , As a result AR2 and AR4 The periodic data between them must pass through the middle area 1, Lead to Waste of resources in the middle area .

1. Use OSPF Virtual links solve irregular areas problem

[r4-ospf-1-area-0.0.0.1]vlink-peer 2.2.2.2

--- The configuration of virtual link must make it bidirectional . 

A virtual link can only cross one area --- The virtual link always belongs to the region 0.

[r2]display ospf vlink --- see VLINK Information

 

Use Virtual links solve irregular areas Of shortcoming ：

1, Because of the existence of virtual links ,AR4 and AR2 We need to establish a neighbor relationship , As a result AR2 and AR4 The periodic data between them must pass through the middle area 1, Lead to Waste of resources in the middle area .

2, Only one area can be crossed

3, many Process two-way republishing

Reissue need The border router running on different protocols at the same time On ,OSPF Such a border router is called ASBR --- Autonomous system border router （ Protocol boundary router ）--- Only the device that performs the republishing action can be called ASBR equipment .

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

Imported Routing information Its mark is ---O_ASE ---- Identified as Extraterritorial routing information --- This part of the route The controllability of information is poor .

LSA ---- Link status notification ---OSPF The agreement Carriers carrying different information produced in different network environments .

LSDB --- Link state database  

SPF --- Shortest path first algorithm

Type ---LSA The type of , stay OSPFV2 In the version , What needs to be mastered LSA type Altogether 6  Kind of .

LinkState ID--- Link state identifier --- Used to mark a LSA Information , It's equivalent to a LSA The name of the message .

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

Link state type , Link state ID, Notify router ----“LSA A triple ” --- Three parameters can uniquely identify one LSA.

LSA The content of the header ：

LSA Triple of

Age ---LSA Aging time --- The unit is s --- When one LSA The information is produced by the router

Born from 0 Start timing , Whole LSA In the whole process of network transmission , The timing is uninterrupted .

When there is a new LSA On arrival , Will overwrite the old LSA Information . In general ,LSA Of

Aging time should be less than 1800S（ because OSPF Every time 1800S A cycle will be carried out

new .） In order to prevent the unlimited growth of aging time , We designed a At maximum aging

between ---MAX age ---3600S ---- When one LSA The aging time reaches the maximum aging

Time time , Will be deemed invalid , Will be from local LSDB Delete .

OSPF Periodic update of Yes, according to each LSA Aging time to time , When one Lsa The aging time has reached 1800S when , Periodic updates will be made , Resend this LSA Information . When the device sends LSA The aging time is close to , But not at the same time , You need to update periodically , Causing waste of resources --- Group pace timer ---300S --- This is an optimization mechanism , When one LSA The aging time of information has reached 1800S after , Periodic updates will not be performed directly , But wait 300S, arrive 2100S After that , The aging time will be reduced to 1800S -2100S Between LSA Information goes together That's ok to update .

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 --- From the minimum to the maximum , Add... In turn 1, Old and new relationships are easy to judge , But the number is limited . 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 --- Serial number can be recycled , The serial number will not be used up , But if the difference between two serial numbers is large , It may cause the old and new relationship to be unable to judge .

3, Lollipop type sequence space ---OSPF This sequence space is used , however , After it enters the circulation part , We will still face the problem of cyclic sequence space , therefore ,OSPF It is required that it cannot be cycled , It is equivalent to a linear sequence space , Its value is 0X80000001 -0X7FFFFFFE.

OSPF Refresh the serial number space Of Method ： When one LSA The serial number of the message reaches 0x7FFFFFFE yes , The router will change its aging time to 3600S, Other devices received this LSA After the message , It will be judged according to the serial number that this is the latest LSA Information , Refresh the change information to the local LSDB in . after , Because of this LSA The aging time of information reaches 3600S, Then put this LSA Delete the information . The originating router will send another one of the same LSA Information , Its serial number uses 0x80000001, Other equipment will send the latest LSA The information is refreshed to LSDB in , Then the serial number space is refreshed .

chksum --- Ensure data integrity --- Checksums also participate LSA A comparison between the old and the new . When two LSA Triples are the same , And the serial number is also the same , Then you can use checksum comparison , If the checksum is large, it is recognized as new .

 

Type -1LSA --- All devices in the network will send , And only send one class LSA. A class LSA Of LSID The value is equal to that of the notifier RID.

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

Link type --- 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 Incomplete information description may occur , 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 .---- The so-called checking calculation 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 the cost value . The target network segment information passes LS ID To carry , It will also contain its mask information . The cost value refers to the cost value of the advertiser reaching the target network segment .