OSPF detailed explanation (LSA) (2)

So let's see ：

Requirements for area division （ Two article ）:

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

2, Regions must be divided according to star topology .

OSPF Irregular areas of ：

OSPF Irregular areas of （ Two kinds of ）：

1, Non backbone areas away from the backbone

2, Discontinuous backbone

Reasons for irregular areas ：

answer ： The topology of the network in the enterprise has been changed , Some upgrades

Solution （ Three ）：（ Both solutions are the same ）

Take the non backbone area away from the backbone as an example ：

reason ：R4 The routing information inside is complete , But it's illegal ABR equipment , Because it's not formal ABR equipment , It doesn't have one               The interface is connected in the area 0 Inside

Method 1 ： Use VPN Tunnel makes illegal ABR Legalization

In the process , One thing you can notice , Namely R4 After creating the virtual private line , 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 The routing information of is sent to R4, and R4 Will unconditionally trust their routing information through topology , Even if the cost value is very large .

Use VPN The tunnel solves the problem of irregular areas shortcoming （ Three ）:

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

2, Repeated updates may occur

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 number of periodicity between         It is believed that they have to go through the middle area 1, This leads to a waste of resources in the middle area .

Method 2 ： Use OSPF Virtual link solves the problem of irregular area ：

Illegal ABR Need to find a legal ABR As guarantor , Make illegal ABR Legalization

[r4-ospf-1-area-0.0.0.1] vlink-peer 2.2.2.2     --- The configuration of virtual link must make it bidirectional .

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

notes ： A virtual link can only cross one area , And the virtual link always belongs to the region 0.

Network type	ospf The network type of the interface ( Operation mode )
BMA( Ethernet )	Broadcast, Multiple neighbors can be established . Need to carry out DR and BDR The election ,hello 10s,dead time 40S
P2P(PPP, HDLC)	P2P, Only one neighborhood can be established , There is no need for DR and BDR The election ,hello 10s,dead time 40S
Loopback interface ( Virtual interface )	P2P, Huawei equipment is defined as P2P type , But in fact, there is no data sending and receiving . Loopback interface default learning 32 Bit host routing
	P2MP, Multiple neighbors can be established , There is no need for DR and BDR The election of ,hello 30S,dead time 120S. Learn the host routing of neighbor interface .
NBMA( Frame relay )	NBMA, Multiple neighbors can be established , Need to carry out DR and BDR The election ,hello 30s,dead time 120S, Unable to automatically establish neighbor relationship
	Virtual, Send as unicast hello package ;hello 10s,dead time 40S

  Use virtual links to solve the problem of irregular areas shortcoming （ Two article ）:

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 number of periodicity between         It is believed that they have to go through the middle area 1, This leads to a waste of resources in the middle area .

2, Only one area can be crossed

Method 3 ： Multi process bidirectional republication

Redistributions need to run on border routers running different protocols at the same time ,OSPF Such a border router is called ASBR（ Autonomous system border router / Protocol boundary router ), The premise is that only the device that performs the republishing action can be called ASBR equipment .

[r4-ospf-2] import-route ospf 1      --- stay ospf process 2 Import ospf process 1（ Bidirectional ）

The flag of the imported routing information is ：O_ASE , It is recognized as extraterritorial routing information , Priority is set to 150, But this                                                 The controllability of some routing information is poor .

LSA：

LSA（ Road status announcement ）：OSPF Protocols are carriers that carry different information in different network environments .

LSDB（ Link state database ）： Inside LSA Information

SPF（ Shortest path first algorithm ）： Use this algorithm to collect LSA Convert to tree structure , Then calculate the local arrival                                                   A routing information of unknown network segment , then , Load the routing information into the routing table

Type： representative LSA The type of , stay OSPFV2 In the version , What needs to be mastered LSA The types are 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.

LSA A triple ： That is, link state type , Link state ID, Notify router , Three parameters can uniquely identify a                           strip LSA,LSA Three tuples are the same LSA, Otherwise, it's not .

[r3] display ospf lsdb router(type) 4.4.4.4(LinkState ID)             --- Expand a specific LSA Information

LSA The content of the header :

LSA Triple of

Age（LSA Aging time ）： The unit is s, When one LSA Information is generated by the router from 0 Start timing , Whole LSA Online                                             The whole process of collateral seed transmission , The timing is uninterrupted . When there is a new LSA On arrival , Will overwrite the old                                              LSA Information . In general ,LSA The aging time of should be less than 1800S( because OSPF Every time                                             1800S There will be a periodic update .)

MAXage： In order to prevent the unlimited growth of aging time , We designed a maximum aging time of 3600S

notes ： When one LSA When the aging time of reaches the maximum aging 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 a device sends LSA When aging                                   Indirect proximity , But not at the same time , You need to update periodically , Lead to waste of resources

Group pace timer ：300S, This is an optimization mechanism , When one LSA The aging time of information has reached 1800S after , Will not be direct                             Update periodically , But wait 300S, arrive 2100S after , The aging time will be reduced to                                 1800S-2100S Between LSA Information is updated together .

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 （ Range of serial number values ）（ Three ）：

1, Linear sequence space ： The value starts from the minimum value to the maximum value , Add... In turn 1, Old and new relationships are easy to judge ; But quantity                                       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 ： Serial number can be recycled , The serial number will not be used up , But if the difference between two serial numbers is compared                                       When I was big , 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 , Will still face                                           The problem of cyclic sequence space , therefore ,OSPF It is required that it cannot be cycled , Equivalent to one                                           A linear sequence space , Its value is 0X80000001-0X7FFFFFFE.

OSPF Method of refreshing space serial number : When one LSA The serial number of the message reaches 0x7FFFFFFE yes , The router will send him                                        The aging time of is changed to 3600s, Other devices received this LSA After the message , Will judge according to the serial number                                               This is the latest LSA Information , Refresh the change information to the local LSDB in . after , because                                             For this LSA The aging time of information reaches 3600s, Then put this LSA Delete the information . beginning                                               The router that sends 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 sequence                     When the number is the same , Then you can use checksum comparison , If the checksum is large, it is recognized as new .

type	LSID	Notifier	Scope of action	Carry information
Type-1 LSA Router	Announcer's RID	All operations in the area OSPF Protocol router RID	Single area	Direct connection topology of local interface
Type-2LSA Network	DR Interface IP Address	Single MA In the network DR On the router RID	Single area	Single MA Supplementary information of network topology information
Type-3LSA Sum-Net(summary)	The target network number of the routing information	ABR, After passing the next ABR The device will be modified to new ABR equipment	ABR Adjacent single areas	Inter domain routing information
Type-5 LSA External(ase)

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                           Announcer's 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 , According to the network type of the interface, he will judge that the interface runs in                       One   What kind of network .

 

StubNet： The Internet

TransNet： Represents the connection in a MA In the network

Type-2LSA（2 class LSA）： stay MA In the Internet , Rely solely on 1 class LSA Incomplete information description may occur , the                                             With , Need to pass through 2 class LSA Supplement the missing information .

notes ： 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 , only             You need a device to send it .

notes ： All that carry routing information LSA All need to pass 1 Classes and 2 class LSA Check calculation .

Checking 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 notifier （ABR set up                         To prepare ） The cost value of reaching the target network segment .