Hcip fourth day notes

One .ospf It is an open shortest path first protocol 、 Classless link state routing protocol     The public agreement 、 Cross layer encapsulation to IP Headlines 、 Agreement No 89、 be based on 224.0.0.5、224.0.0.6 Multicast update

Trigger update 、 Cycle update （30min）

Need structured deployment ： Area division and address planning

Two .ospf Characteristics

a. Regional concept , Effectively reduce routing entry pairs CPU And memory usage , Limit topology changes to this region , The details of the LSA Flood control
b. Adjacency relations .OSPF The protocol defines some router types and network types , The establishment of adjacency relationship is exchange Hellow Information router type and exchange Hellow The network type of information determines
c. Each receives a message from a neighbor router LSA Your router will put these LSA Record in its LSDB in , And send a copy LSA Copy to this router and all other neighbors .
d. When these routers LSDB Exactly the same , Take oneself as the root , Use SPF The algorithm computes a acyclic shortest path topology . To build your own routing table .

3、 ... and .ospf Five kinds of bags

Hellow： Find neighbors and establish adjacency

DBD： Check whether the databases of the router are synchronized

LSR： Request a specific link state from another device

LSU： Send link status information

LSACK： Confirm the multi segment sending message

Four .ospf Table of

1、  Routing table ： List through SPF The algorithm calculates the best path to each connected network  
2、 Link state database ： List information about other routers in the network , This shows the whole network Network topology
3、  Neighbor list ： List each Router All neighbor routers that have established adjacency relationships

5、 ... and .ospf Working process of

After the startup configuration is completed , Neighbors start sending and receiving hello package ;hello The package will carry the local and all known local neighbors rid; Then generate the neighbor table ; Neighbors need to pay attention to whether they can become adjacency conditions ; If it cannot be established as adjacency , Will remain a neighbor , only hello Just keep the package alive for a period ;

If adjacency can be established ; Will use DBD Compare local database directories ; Then based on the results of comparison , Use LSR/LSU/LSack To get local unknown LSA Information ; Make the database between adjacency relationships （lsdb） Complete synchronization （ Agreement ）, Generate database tables ;

After that, it is based on lsdb, Use spf Algorithm , Generate directed graph —> Shortest path tree ——＞ Calculate the shortest local path to all unknown network segments , Load it into the local routing table ; Convergence complete ;

After convergence , Neighbors and adjacency are hello Every time 10s Keep alive ; Every time 30min A periodic database comparison between adjacent relationships , Guarantee consistency

6、 ... and .ospf Various types LSA

1 class LSA-route

2 class LSA-network

3 class LSA-summary

4 class LSA-asbr

5 class LSA-ase

7 class LSA-nssa

1. Router LSA.（Router LSA）

Every device produces , Describes the link state and overhead of the device , The LSA Flooding can only occur in the area to which the interface belongs

2. The Internet LSA（Network LSA）

from DR produce , Describe the DR Connected MA All routers in the network that form an adjacency relationship with it , as well as DR own . The LSA Flooding can only occur in the area to which the interface belongs

3 Network Summary LSA（Network Summary LSA）

from ABR produce , Describe the route of a network segment in the area , This kind LSA It is mainly used for routing between regions

4ASBR Summary LSA（ASBR Summary LSA）

from ABR produce , Describe to ASBR The routing , Notice to remove ASBR Other relevant areas in the region .

5.AS external LSA（AS External LSA）

from ASBR produce , Used to describe arrival OSPF Extraterritorial routing

7. Incomplete ending area LSA

（NSSA LSA）

from ASBR produce , Used to describe arrival OSPF Extraterritorial routing .NSSA LSA And AS external LSA The function is similar to , But the flood range is different .NSSA LSA Only at the beginning NSSA Internal flooding , And can't directly enter Area0.NSSA Of ABR Will 7 class LSA convert to 5 class LSA Injection into Area0