OSPF dynamic routing protocol learning notes

It is very useful to know about dynamic routing protocols. Here we will mainly introduce the full explanation of OSPF dynamic routing protocols. Today, with the rapid development of the Internet, TCP/IP has become the mainstream protocol for data network interconnection. All kinds of routers running on various networks are responsible for controlling traffic that may be the most important information of this century. The collaboration between these hundreds of routers is inseparable from dynamic routing protocols.

OSPF and OSPF are both good dynamic routing protocols in recent years. OSPF has been widely used in many manufacturers with high protocol standardization. However, the OSPF protocol was invented by Cisco, a leading provider in the network industry, it is also widely recognized by users based on its influence in the industry and its absolute market share. However, which of the two dynamic routing protocols is better? Who is more suitable for the future development of the network? This article analyzes the advantages and disadvantages of these two dynamic routing protocols from a technical perspective, so that network integrators and enterprise users can serve as a reference in network design and planning.

OSPF protocol

OSPF is the abbreviation of Open Shortest Path First ("Open Shortest Path First Protocol. It is a link-state-based dynamic routing protocol developed by IETF. On an IP network, it dynamically discovers and transmits routes by collecting and passing the link status of the autonomous system.

Each router running the OSPF protocol always describes the connection status of the local network (such as available interface information and accessible neighbor information) in LSA (broadcast link status, and broadcast it to the entire autonomous system. In this way, each router receives the LSA generated by all the routers in the autonomous system. These LSA sets constitute the LSDB (link status database ). Since each LSA describes the network topology around a vro, the entire LSDB is a true reflection of the network topology of the autonomous system. Based on LSDB, Each router runs the SPF (Shortest Path First) algorithm. Build a self-rooted Shortest Path Tree that provides routes to nodes in the autonomous system. In graph theory, "Tree" is a non-loop join graph. Therefore, the routes calculated by OSPF are also non-loop routes. To reduce the overhead of OSPF, the following concepts are proposed:

(1 ). DR: if there are two or more vrouters in various networks that can be accessed by multiple access, a "designated vro" (DR) should be selected on the network ). The "specified vro" synchronizes the LSDB with all vrouters in this segment. In this way, no LSDB synchronization is performed between two non-DR routers. This greatly saves the bandwidth overhead within the same network segment.

(2 ). AREA: OSPF can be divided into different regions according to the topology of the autonomous system. In this way, when the Regional Border Router (ABR) sends route information to other regions, the Digest LSA is generated in units of network segments. This can reduce the number of LSA in the Autonomous System and the complexity of route computing. Intra-and inter-region routes describe the internal network structure of the autonomous system, while external routes describe how to select routes to destinations outside the autonomous system. Generally, the first type of external routes correspond to the information introduced by OSPF from other internal routing protocols. The cost of these routes is comparable to that of OSPF routes; the second type of external routes correspond to the information introduced by OSPF from the external dynamic routing protocol. Their cost is much higher than the OSPF route cost. Therefore, only the external cost is considered during computing.

Main advantages of OSPF:

1. OSPF is a real LOOP-FREE dynamic routing protocol. Derived from the advantages of the algorithm itself. (Link status and Shortest Path Tree Algorithm)

2. Fast OSPF convergence: route changes can be transmitted to the entire Autonomous System in the shortest time.

3. The concept of area Division is proposed. After the autonomous system is divided into different regions, the route information digest between regions greatly reduces the number of route information to be transmitted. In addition, the routing information does not expand rapidly as the network size expands.

4. Minimize the overhead of the dynamic routing protocol. See:

1) The hello messages without routing information are sent regularly to discover and maintain the neighbor relationship, which is very short. The update mechanism is triggered when packets containing route information are sent. (Sent only when there is a route change ). However, to enhance the robustness of the dynamic routing protocol, all requests are resold once every 1800 seconds.

2) In broadcast networks, multicast addresses (rather than broadcasts) are used to send packets, reducing interference with other network devices that do not run ospf.

3) in various networks (broadcast, NBMA) that can be accessed by multiple access, the number of Route switching (synchronization) times between routers in the same network segment is changed from O (N * N) the number of times is reduced to O (N.

4) propose the STUB region concept so that the introduced ASE route will not be transmitted in the STUB region.

5) supports route aggregation on the ABR (Regional Border Router) to further reduce route information transmission between regions.

6) in the point-to-point interface type, OSPF over On Demand Circuits is configured so that ospf no longer regularly sends hello packets and regularly updates route information. Update information is sent only when the network topology changes.

5. Provide more trusted routing choices by strictly dividing the route levels (which can be divided into four poles.

6. Good security. ospf supports interface-based plaintext and md5 verification.

7. OSPF can adapt to a variety of networks, with a maximum of thousands.