Hcip day 6 notes

OSPF Requirements for area division ：

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

        2, The area division must be carried out according to the star topology ;

Common irregular areas ：

1, Non backbone areas away from the backbone

2, Discontinuous backbone area

Non backbone areas away from the backbone

 1, Use VPN Tunnel

Directly in illegal ABR Build a tunnel to reach the backbone area , Equivalent to straight Pick up the illegal ABR Connected to the backbone area , After that, the interface is connected in the backbone area live , An illegal ABR Become legal ABR, You can route normally forward . Realize the communication of irregular area .

Something to watch out for ：

1, When one ABR When connecting backbone areas and multiple non backbone areas at the same time , Non backbone area Domains will pass directly through this ABR To deliver routing information , Without going through the backbone Area .

2, When routing information is learned from both backbone and non backbone areas , The equipment will be free Select the information sent from the backbone area , Instead of messages sent by non backbone , Even bone The overhead value of information sent in the dry area is greater .

shortcoming ：

1, because OSPF Will give priority to the routing information learned from the backbone area , therefore , Probably It will cause the problem of poor route selection

2, After connecting through the tunnel , Illegal ABR Become legal ABR after , Will be directly connected Passing area 0 Learn the routing information of the backbone area , It will also pass through the area 1 Learning area 0 Routing information for , Result in repeated updates .

3, Because of the existence of virtual links ,AR2 and AR4 We also need to establish a neighbor relationship , the With , The periodic data between neighbors need to pass through AREA 1 To pass , Would be right Area 1 Additional loss of resources .

2, Use OSPF Virtual link to complete information transmission

The virtual link is configured in the area that the virtual link needs to pass through .

[r4-ospf-1-area-0.0.0.1]vlink-peer 2.2.2.2 --- This one at the back 2.2.2.2 It is the neighbor who needs to establish a virtual link RID

Be careful ： The virtual link needs to be established by both parties at the same time to take effect .

The virtual link always belongs to the region 0.

shortcoming ：

1, Because of the existence of virtual links ,AR2 and AR4 We also need to establish a neighbor relationship , the With , The periodic data between neighbors need to pass through AREA 1 To pass , Would be right Area 1 Additional loss of resources .

2, Virtual links are limited to only one area

3, Multi process bidirectional republication We redistribute the configuration on routers running different protocols ,OSPF Put such a route The device is called ASBR（ Autonomous system border router / Protocol boundary router ） shortcoming ： Published routes are all extraterritorial routes , Poor controllability .

OSPF Of LSA

LSA --- Link status notification --- OSPF The protocol is carried and transmitted in different network environments Information delivered

LSDB --- Link state database

SPF ---- Shortest path first algorithm

LSA Head content ：

TYPE --- describe LSA The type of （ stay OSPFV2 in , The main thing is to master 6 in LSA type ） LinkState ID --- Link state identifier --- Its function is to mark a LSA Information .（ One LSA The name of ）

--- Because of the different types of LSA obtain LS ID It's not the same way , therefore , Probably There will be LS ID Repetition . therefore , Just by LS ID It cannot be uniquely identified Make one LSA

AdvRouter --- Notify router --- The ID sends the message LSA Information router RID.

The above three parameters are called LSA“ A triple ” ---- It can uniquely identify one LSA Letter Rest .

LS AGE --- Aging time --- Company S --- This aging time is from the LSA From the beginning Start timing when it is generated in the router ,（ Not to join LSDB Start timing after ）, And after , The LSA The whole communication process in the network , Aging time always accumulates . ---- commonly The maximum aging time reaches 1800S. ---- Maximum aging time --- MAX AGE --- 3600S ---- When one LSA The aging time reaches 3600S when , It will be deemed that LSA Information invalid , Delete directly .

SEQ -- Serial number --- from 32 Bit binary structure , use 8 position 16 It's expressed in hexadecimal --- Every jump LSA Will carry a serial number , Mainly used to distinguish LSA New and old . Each router The transmitter is sending the same LSA Information will carry a serial number , And the serial number one by one Add 1.

Classification of serial number space

Linear serial number space --- advantage , Convenient, old and new , Pass the level Department can directly compare ; shortcoming , The space of serial number is limited , When the excess space is large Small restrictions , You will not be able to compare size relationships properly .

Cyclic serial number space --- advantage ： Serial numbers can be recycled , Not subject to Limitation of space size ; shortcoming , When two LSA The serial number carried is different large , It is impossible to judge the old from the new .

Lollipop type serial number space --- OSPF Take the lollipop type sequence empty between , however , In order to avoid the situation that the old and the new cannot be judged by the circulating part , the With ,OSPF It is required that the serial number cannot enter the cycle .OSPF Value range of serial number 0X80000001 - 0X7FFFFFFE.

OSPF Method of resetting serial number space ：

When one LSA The serial number of has reached the maximum 0X7FFFFFFE when , We will Will set his aging time to the maximum aging time 3600S. neighbor Here you go LSA After the message , Will follow the latest LSA Information Office The reason is , The same local LSA Refresh the information . after , Because old Time to 3600S, Then the LSA Information deletion . Then , The device will send the same message again LSA Information to neighbors , This article LSA The information in is the serial number 0X80000001. Then the neighbors will put the latest Of LSA Information added to LSDB In the database , To refresh the serial number The function of space .

Chksum --- The checksum ---- The main task is to verify the integrity of data --- This check And will also participate LSA A comparison between the old and the new . That is, when two are the same LSA Their serial numbers are the same , Then it will be judged by checksum , If the checksum is large, it is recognized as new .

OSPF Periodic update of --- 30MIN（1800S） --- Group pace timer ---

300S ---- Under normal circumstances , When one LSA The aging time of information reaches 1800S when , take Update periodically . however , If the group step timer is turned on , achieve 1800S when , There will be no periodic updates , But wait 300S（ Group pace timer ）, When aging time arrive 2100S when , Then update periodically , And will be updated at the same time LSDB All aging in Time in 1800S - 2100S In the interval LSA Update the information together .

type     LSID     Notifier      The scope of communication      Carry information
Type - 1LSA Router     Notify router Of RID     All operations in this area OSPF Protocol router Of RID     Single area      Local interface direct connection Topology information
Type - 2LSA Network    DR Interface IP Address      Single MA Network DR Of the router RID     Single area      Single MA Online Complement of topology information charge
Type - 3LSA SumNet（summ ary）     The destination of the route Segment information     ABR equipment         
Type - 1LSA --- All routers in the network need to send and only send one .

LINK --- Every one of them LINK Are used to describe the connection of the router interface . One interface can use more than one LINK To describe .

LINK TYPE --- This link type , The network type mainly connected with the interface of , He will judge that the interface is connected in a according to the encapsulation protocol of the specific interface What kind of network .

 Type - 2LSA --- In the face of MA In the description of the network , Rely solely on 1 class LSA Unable to get complete Internet information , therefore , We introduce 2 class LSA To supplement . --- because 2 class LSA It's all public information , therefore , One MA You only need one in the network 2 class LSA that will do , also , The 2 class LSA By this MA In the network DR send out . Avoid repetition new .

OSPF Regulations , All delivery routes LSA Information must go through topology information （1 Classes and 2 class LSA） Checking calculation of . --- Find the advertiser of routing information through topology information

Type - 3LSA --- Main routing information between domains , Notifier is inter domain ABR equipment ,LS ID The network number that routes the advertisement . The parameters carried by itself are mainly two , A sub of a target network segment Netmask , Another is the cost of the advertiser reaching the target network segment .