OSPF (sixth day notes)

OSPF Irregular areas of

Requirements for area division ：

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

2、 Region division must be based on star topology

Irregular areas ：

1、 Non backbone areas away from the backbone

2、 Discontinuous backbone

solve OSPF Method of irregular region of

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 disadvantage of irregular areas ：

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 periodic data between them must pass through the middle area 1, This leads to a waste of resources in the middle area

2, Use OSPF Virtual link solves the problem of irregular area

[r4-ospf-A-area-0.0.0.1]vink-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 vink see VLINK Information

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 ,hella 105,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 ,helo 30S,dead time 120S, Unable to automatically establish neighbor relationship

virtual, Send as unicast hello package ;hello  10s,dead time  40s

The disadvantage of using virtual links to solve irregular areas ：

1、 Because of the existence of virtual links ,ARA 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, This leads to a waste of resources in the middle area .

2、 Only one area can be crossed

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 ）-—- Only the device that performs the republishing action can be called ASBR equipment

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

The routing information of the guide is marked O_ASE, It is recognized as extraterritorial routing information , The controllability of this part of routing information is poor .

LSA（ Link status notification ）OSPF Protocols are carriers that carry different information 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 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

Link state type 、 Link state ID、 The notification router is called “LSA A triple “ Three parameters can uniquely identify one LSA

 

LSA The content of the head ：

LSA A triple

Age,LSA Aging time , The unit is S, When one LSA Information is generated by the router 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 The aging time of should be less than 1800S（ because OSPF Every time 18005 There will be a periodic update ） In order to prevent the unlimited growth of aging time , We designed a maximum aging time ,MAX age=3600S, When one LSA When the aging time of reaches the maximum aging time , Will be deemed invalid , Will be from local LSDB Delete

OSPF The periodic update of is based on 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 The aging time is close to , 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 , Periodic updates will not be performed directly , But wait 300S, arrive 2100S after , The aging time will be reduced to 1800S －2100S Between LSA Information is updated together

 

Serial number

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 , May lead to new

Old relationship cannot be judged

3, Lollipop type sequence space

OSPF This sequence space is used , But 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 , Equivalent to a linear sequence space, its value 0X80000001-0X7FFFFFFE,OSPF Method of refreshing space serial number ： When one LSA The serial number of the message reaches 0X7FFFFFFE when , 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 .

LSA Categories

 

Type-1LSA ：

All devices in the network will send , And only send one class LSA, A class LSA Of LS ID The value is equal to that of the notifier RID

UINK—— Parameters used to describe the connection of router interface , One interface can use more than one uink 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 one device

Just send it

 

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

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