OSPF (1) Opening Remarks

Hello everyone, my name is Open Shortest Path Fist. The Chinese name is "Open Shortest Path First.
What? Why is there an "Open" in the name "? Is it "open? Relatively speaking, it is indeed. I am an Internet Engineering Task Group. This name is awkward. Let's say it in English. "Internet Engineer Tast Force"-"IETF" for short ", developedDynamic Routing Protocol.I have to mention that IETF, my creator, is a loose, self-disciplined, and voluntary civil academic organization. No matter what you think, I like these words, A feeling of Internet spirit ). Back to the "open" topic, I am not owned by any vendor or organization, and everyone can use it for free. Comparatively, there is another guy called "VPN", which was developed by Cisco. He is actually very powerful. The convergence speed is a fast one. It is also very powerful, and the measurement value algorithm is well-rounded. But now there are not many people using him, because Cisco has privatized him and won't be used by other vendors. Therefore, although it is powerful, it does not have much space to display. OSPF is like Microsoft's Windows, while VPN is like Apple's Mac OS. Yes, Mac OS is stable, simple, intuitive, secure, and fast. However, he only runs on a MAC computer, and other computers can only drool, or he can toss a "black apple" on his own ". While Windows is another path, compatible, No matter what computer, as long as it is a X-86 architecture, directly installed to run up. As a result, Windows has a large share of the market, and other computer manufacturers are also very supportive and welcome, although you still have to pay a license fee. So OSPF has another nickname-"Enterprise Network overlord ". As a dynamic routing protocol, the main task is to learn routing and maintain the route table. Unlike RIP,Link Status Protocol. RIP puts its ownOptimal Route informationPut it in your Response package and send it out. However,Router links, interfaces, neighbors, and link information"Express connectLSABut because I have made a very detailed distinction between the links, there are also 11 types of LSA, and I will talk about LSA later. Now let's take a closer look at my working process: first, I will send a packet "Hello" to say Hello on the advertised port. If you receive my "Hello ",NeighborsNeighbor). But my "Hello" package contains information, and the amount of information is not small, but it is important that there are two, "Five marked bits of the logo availability" K value) and "Hello interval ". If you have configured authentication, there will be related authentication content. After the router receives the "Hello" packet, the corresponding settings are matched. If yes, proceed to the next step and createAdjacency ).After the "adjacent" relationship is established, "Link Statement Advertisement" will be sent"LSA) This packet contains various link status information. The router records the LSA in its own "link status database" and sends a copy of its neighbor. In this way, the LSA will be widely transmitted to the whole region. When the databases of these routers are all the same, each vro takes its own root and uses the SPF algorithm to calculate a non-ring topology. The calculation result is the shortest path of each vro, and put it in the route table. For forwarding. After a route table is created successfully, I will "quiet" and only send the "Hello" packet to perceive the existence of the affinity Keepalive ). In short, the dynamic routing protocol can be divided into two ways based on its learning and computing routing:Distance vector protocolThe neighbor is the finished product. Only the optimal route is provided. WhileDistance vector protocolIt is a semi-finished product, giving you all the link statuses of your own, and how to choose the specific link status. Then, you can choose the desired link based on your own algorithm. Finally, we need to add some basic information about OSPF: a pure classless Router Protocol that supports VLSM Variable Length subnet mask) and CIDR (classless Inter-Domain Routing ). OSPF does not know what A/B/C/D/E/F network is, but only knows the subnet mask. The OSPF management distance IS 110, which IS inferior to that of static routes: 1), EIGRP90), and EBGP20. It IS superior to IS-IS (115), RIP120), ExEIGRP170) and IBGP200 ). A protocol with a higher priority. The COST calculation method of the metric value, "100 M/bandwidth", with decimals used in one method for processing. Of course, the bandwidth on the current backbone network is measured in GB. Therefore, OSPF can flexibly modify the "M" standard to meet the needs of modern networks. OSPF is a layer-3 protocol, which is directly encapsulated in the IP layer, that is, the layer-3 protocol. Therefore, only the Protocol Number is 89.