Basic routing knowledge: detailed introduction to OSPF Routing Protocol

Many people may not know much about the OSPF routing protocol. Here we will mainly explain the detailed introduction of the OSPF routing protocol. Here we will share it with you and hope it will be useful to you. Link State packet type in the region:

1. Router LSA

It is generated by all vrouters in the region and can only be broadcast in flood scenarios in the region.

2. Network LSA

Generated by the DR or BDR router in the region. The packet includes the link information of the router connected to the DR and BDR.

3. Network Summary LSA

If an API is generated, it notifies the routers in the same region of the route information to the route information outside the region. At the same time, it can send default routes to different regions in the same Autonomous Region. routes in the same region are sent to the backbone region, if there are two paths to the same destination, only the routes with the lowest cost will be sent;

4. ASBR Summary LSA

It is generated by the API, but it is a host route, pointing to the ASBR router route.

5. Autonomous System External LSA

Generated by ASBR, which tells the vro of the same Autonomous Region to the path of the external region.

6. NSSA External LSA

Generated by ASBR. In The NSSA region, when one vro is an ASBR, the LSA 5 packet has to be generated, but The NSSA cannot contain the LSA 5 packet. All asbrs generate the LSA 7 packet, to the vro in the region. OSPF Over Demand Circuits is used in a link with a switched virtual circuit. When the link is idle, it does not have a virtual circuit connection. Only when there is traffic on the link, to create a virtual circuit. However, the OSPF Hello and LSA packets are sent at intervals, while the Demand Circuits provides a feature, on the virtual circuit, you only need to transmit Hello and LSA packets for the neighbor and Database Synchronization of the OSPF routing protocol. Then, you do not need to send the preceding packets, the LSA will not expire because it cannot receive the Update message, and its neighbor relationship will not be Dead. This reduces the use of links and saves the cost of WAN links.

The OSPF Routing Protocol sets a DonotAge byte in the LSA message to negotiate the two ends so that the received LSA will never expire. In addition, a flag, DC bit, is added to the LSA so that other routers know that the LSA has the characteristics of Demand Circuit, so that other routers do not think that this route has expired. The configuration of OSPF routing protocol has only some characteristics, which are more common.) The OSPF Routing Protocol has the DNS function and can replace the Router ID with the Router name.

Configuration:

The OSPF Routing Protocol provides a solution for an interface with multiple addresses:

1. The OSPF Routing Protocol processes the routing information of the secondary IP address Network only when the main address of the interface enables the OSPF routing protocol.

2. The OSPF routing protocol regards the secondary IP address Network as the Stub Network. There are no OSPF routing protocol neighbors, and no Hello messages are sent or links are formed with the slave address Network. Therefore, when there is a vro attached to the secondary IP address Network and the routing information of the two routers is required, you can consider using static routing.

The Area 1 nssa no-summary no-redistribution command is used on both the ABR and ASBR, so that only the Router LSA and no other types of LSA can be connected to the NSSA region, even LSA 7 does not exist. There is only one default route pointing to the ABR. The Area 1 nssa no-redistribution default-information-originate command enables LSA 3 and 4 to enter the NSSA region in the preceding cases, but LSA 5 and LSA 7 are filtered out. After removing no-summary, although LSA 3 and 4 can enter the NSSA region, the ABR cannot generate a default route pointing to the outside network, isolate routers in the NSSA region from routes outside the autonomous region. You can use the default-information-originate parameter to generate a default route. When configuring Address Aggregation on the OSPF routing protocol, it is best to add a default route pointing to the null0 port on the ABR to prevent route loopback.