Shulou(Shulou.com)06/02 Report--

Directory: 1. OSPF definition 2. OSPF application environment 3. OSPF's five major areas 4. OSPF's 4 routing types 5. OSPF's 5 big data packet types 6. OSPF's seven states 7. OSPF's four network types 8. OSPF's six LSAI.OSPF definitions

OSPF routing protocol is a typical link-state (Link-state) routing protocol, which is generally used in the same routing domain.

two。 In this case, the routing domain refers to an autonomous system (Autonomous System), namely AS, which refers to a group of networks that exchange routing information with each other through a unified routing policy or routing protocol.

In this AS, all OSPF routers maintain the same database describing the AS structure, which stores the state information of the corresponding links in the routing domain, and the OSPF router calculates its OSPF routing table through this database.

4. As a link-state routing protocol, OSPF delivers link-state broadcast packets LSA (Link State Advertisement) to all routers in an area, unlike distance vector routing protocols. A router running a distance vector routing protocol passes some or all of its routing table to its neighboring router.

The working process of 5.OSPF:

2. OSPF application environment 1. Consider the following aspects of the use of OSPF network size network topology other special requirements of the router itself 2.OSPF can adapt to large-scale network routing changes convergence speed non-routing loop support variable length subnet mask support area partition support a multicast address sending protocol comparison between 3.OSPF and RIP

In order to adapt to the large network, OSPF divides multiple areas within the AS. Each OSPF router only maintains the complete link-state information of the area. 2. Region ID region ID can be expressed as a decimal number or as an IP

3. Type of region backbone area

The ID of the backbone area is Area 0, which is responsible for the standard area of inter-area routing information dissemination.

When a region lacks customization, it is considered to be the terminal area of a normal area (STUB)

An area storage stub area (Totally Stubby) that does not allow AS external LSA to flood inside the device

That is, the complete stub area, which is the most restricted form of non-stub area (NSSA).

Allow some external routers to advertise inside the OSPF autonomous system while retaining the characteristics of STUB in the area part of the autonomous system. Four routing types of 1.Router ID:OSPF area 2.Router ID selection rules that uniquely represent the IP address of the router: select the IP address with the highest value on the lookback interface of the router if there is no lookback interface The one with the highest IP address in the physical port can also use the router-id command to specify the Router ID3.4 type: DR (main internal router)

In a broadcast, multi-access network, such as Ethernet, TokenRing, and FDDI environments, there is a designated router (Designated Router)

The designated router mainly completes the following tasks in the OSPF protocol: the designated router generates a link packet-network link that describes the network segment in which it is located, which contains the status information of all the routers on the network segment, including the designated router itself. The designated router establishes adjacencies with all OSPF routers that are on the same segment as it. Because the link-state database between OSPF routers is synchronized by establishing adjacency and later flooding, we can say that the designated router is at the center of a network segment.

BDR (secondary internal router)

BDR can automatically replace all the work of DR after the failure of DR

ABR (area Border Router)

When a router is connected to multiple areas, we call it an area boundary router. The area boundary router runs the OSPF algorithm defined by all areas connected to it, has network structure data for each connected area, and knows how to broadcast link-state information for that area to the backbone area, which is then forwarded to the rest of the area.

ASBR (AS Border Router)

The AS border router is an OSPF router that exchanges routing information with routers outside the AS. The router broadcasts the AS external routing information it gets inside the AS, so that all routers inside the AS know the routing information to the AS border router. The definition of AS border router is independent of the definition of previous routers. An AS border router can be an area internal router or an area border router.

The election methods of 4.DR and BDR:

1. Automatically elect DR and BDR

The largest router of Router ID on the network segment will be elected as DR, and the second largest will be elected as BDR.

two。 Manual election of DR and BDR

The priority range is 0-255. The higher the value, the higher the priority. The default is 1.

If the priority is the same, you need to compare Router ID

If the priority of the router is set to 0, he will not participate in the election of DR and DBR

5. Note:

The priority of the router can affect an election process, but it cannot force the replacement of existing DR or BDR routers

6.OSPF Multicast address: metric of 224.0.0.5224.0.0.67.OSPF the metric of OSPF is the 8th power of COSTCOST=10 / BW (bandwidth) the shortest path is calculated based on the cost (cost) specified by the interface

5. Five big data packet types 1.OSPF packets: Hello packets carried in IP packets with protocol number 89OSPF: used to discover and maintain neighbor relations, elect DR and BDRDBD database description packages: used to send summary information to neighbors to synchronize link-state database LSR link-state request packets: send after the router receives the DBD containing new information Used to request more detailed information LSU link-state update packet: send link-state advertisement (LSA) after receiving LSR. A LSU packet may contain several LSALSAck link-state acknowledgement packets: confirm that LSU has been received, and each LSA needs to be acknowledged separately. Six. Seven states of 1.DOWN

The state of not enabling OSPF:

Change to this state after neighbor failure

2.INIT statu

Initialization status:

The first time you receive a hello packet from the peer (including the peer route-id), set the status of the peer to init

3.2-WAY status (elects DR BDR, but does not confirm)

Neighbor status:

The status of periodically sending hello to each other (both parties establish a conversation)

4.EXSTART status (confirm DR BDR)

Initialization status of the exchange information:

Send the DBD (containing the summary information of the local LSA) message, elect the master-slave router (use the ID and priority in the HELLO message to conduct the election, do not allow preemption, DR is gone, DBDR can be on)

5.EXCHANGE statu

The status of exchanging information:

In this state, send DBD to each other to inform the peer of the directory of all local LSA; at the same time, you can send LSR,LSU,LSACK to learn the LSA of the peer.

6.LOADING statu

The state of loading (the state of not having finished learning):

Send LSR,LSU,LSACK to learn the details of the peer LSA.

7.FULL statu

Adjacency status (state of completion of learning):

LSDB synchronization with each other, that is, all LSA are the same

Seven. Four network types of OSPF 1. Point-to-point network (Point-to-Point) 2. Broadcast multiple access Network (Broadcast MultiAccess, BMA) 3. Non-broadcast multiple access Network (None Broadcast MultiAcess,NBMA) 4. Point-to-Multipoint Network (Point-to-Multipoint) VIII. Six LSA of OSPF

1.TYPE1:

Router LSA: issued by a router in the area

2.TYPE2:

Network LSA: issued by DR in the area

3.TYPE3:

The network summarizes the total link advertisements sent out by LSA:SBR and other areas

4.TYPE4:

ASBR summary sent by LSA:ABR to advertise ASBR information

5.TYPE5:

Issued by AS external LSA:ASBR to advertise external rout

6.TYPE7:

Issued by ASBR within the external LSA:NSSA area of NSSA to advertise external routes in this area

External path of type 1 (Type 1 external path,E1)

External path of type 2 (Type 2 external path,E2)

7. LSA allowed to flood in each area

nine。 Route redistribution

1. A single IP routing protocol is the preferred scheme for managing IP routing in a network.

2.Cisco IOS can execute multiple routing protocols, each of which belongs to the same autonomous system as the network served by the routing protocol.

3.Cisco IOS uses the route redistribution feature to exchange routing information created by different protocols

4. Considerations for route redistribution:

Measurement value

Administrative distance

5. Type of path redistributed to the route in the OSPF domain

ten。 Virtual link 1. Definition: a link that connects to a backbone area through a non-backbone area. Objective: to connect a region to a backbone area through a non-backbone area and a segmented backbone area through a non-backbone area.

3. The rules and characteristics of configuring virtual links the virtual link must be configured between two ABR routers the transfer area cannot be a stub area the stability of the virtual link depends on the stability of the area it passes through, the virtual link helps to provide logical redundancy. Related configuration codes

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