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Recently, I was studying the global catastrophe accident on the Internet. I suddenly saw this latest accident and felt very enlightening, so I share it with everyone. Cause and effect On June 24, 2019, a telecommunications operator in Pennsylvania named "DQE (AS33154)". The company learned BGP global routing from AT & T and optimized it using the BGP optimizer. The so-called optimization is to extend the network mask bit of the route to make the route more detailed. For example, 104.20.0.0/20, after optimization, becomes two routes, one is 104.20.0.0/21 and the other is 104.20.8.0/21. If the optimized route is only used in its own AS, there is no problem at all, but it must not be advertised through BGP. Routing rules According to the "longest match" routing rule of the route, 104.20.0.0/21 or 104.20.8.0/21 is definitely better than 104.20.0.0/20, so the traffic on the Internet accessing "104.20.0.0/20" will pass DQE Transit.

Anycast over IPv4 The implementation method of Anycast is generally to start the loopback of the same address on the server and implement it by the equivalent routing method. The problem is: 1. What is the need for network elements? 2. Is it simply announced on the routing protocol? 3. Is there a difference between different protocols (ospf, bgp)? 4. What is the impact of route convergence on services? Anycast technology has also been introduced in previous articles, and interested students can go to read it. What is Anycast? Let me cite an example in life. The earliest large supermarket opened on Gubei Shuicheng Road. This is the only supermarket in Asia with the highest annual sales. It is often crowded with water, and even Pudong people come from far away. It didn't take long for a large supermarket to open more than a dozen in various districts of the city. Customers usually went to the nearest one, so that customers were diverted, less crowded, user sa

The current project always mentions VLAN. No matter whether Party A has this requirement or not, VLAN must be switched at Layer 3. This brings a misunderstanding. Many people mistakenly believe that VLAN is a function only available for Layer 3 switches. I thought VLAN itself should belong to Layer 2 technology, and Layer 3 switching is only used for communication between VLANs. This talent is very shallow, and I also invite big coffee to discuss whether VLAN belongs to Layer 2 technology or Layer 3 technology? Let's use the examples in life to compare what VLAN is and what problems it solves. In a city center, some big houses are often used for group rent, and sometimes the big living room also puts a few beds for rent. People who sleep in the living room are definitely uncomfortable, because there are snoring, molars, and Sleepwalkers, and those who talk about dreams, have chicken feathers everywhere. In order to overcome the above mutual interference, the second

Network delay refers to the time elapsed since an IP packet is sent from the source host process and reaches the destination host process, in milliseconds. The IP packet passes from the source host through multiple relay devices, such as switches and routers, and finally reaches the destination. The network delay is composed of the following three: Network delay = transmission delay + processing delay + buffer queue delay Propagation delay This delay is well understood, referring to the delay of light and electrical signals on a wired medium, or the delay of radio signals in an air medium. This transmission delay is only related to the speed of light or the transmission speed of electrical signals. . For a selected end-to-end path, this value is constant. Processing delay Receive IP packets, query forwarding table, hardware or software forwarding, including encapsulation, decapsulation, encoding, decoding time, the more the device passes, the weaker the device th

I often see the words "cloud" and "cloud computing" on the Internet. I didn't know what these words meant, so I went to Baidu Encyclopedia and found that the more I looked at it, the more confused I was. Here, I would like to ask you to summarize the meaning of these two words in one or two simple and easy-to-understand words (try to explain in easy-to-understand words. Cloud / Cloud Computing If you have called the 114 telephone number search desk, it is very easy to understand "cloud" and "cloud computing"! The operator of the 114 phone is the "cloud", and the operator searches the database for the information you want to query and returns the phone number to you. The whole process is "cloud computing". The three numbers 114 are the user interface provided by "cloud computing", simple and convenient! As for whether the "cloud" is a handsome guy or a robot, the "cloud" is sitting

Although this question is a bit absurd, it is of great value for discussion. Whether it is an IPv4 or IPv6 address, it is globally unique on the Internet. You can uniquely identify the host by relying on the IP address only. What else is the MAC address? That's right, very logical! Can the three modes of communication be solved perfectly only by relying on IP addresses? No problem at all! Unicast How does the current network work? The MAC address is embedded in the second layer of the data packet, and the data packet reaches the destination host. The destination host decides whether or not to receive it based on whether the MAC address is the same as its own. How does it work without a MAC address? The second layer of the data packet does not have a MAC address, and the data packet reaches the destination host. The destination host decides whether to receive it based on whether the IPv4 / IPv6 address is the same as its own. IPv4 / IPv6 address, how

I remember when I was a kid, the open-top truck pulled a cart of apples from the orchard, transported it to the dock, and then loaded it onto a 10,000-ton freighter and shipped it to Shanghai. But the last mile to the pier, the roads are bumpy, and the truck will slow down. At this time, some teenagers will climb on the truck and take the apples from the bag to eat. Every time, one or several bags will be unpacked for this purpose. The company is very distressed. Later, in order to reduce losses, the transportation company used closed containers, loaded the apples and then locked the car, arrived at the destination and then opened, so that even if someone wanted to take the apple from the car, they could not start. The above convertible truck corresponds to TCP, and Apple corresponds to HTTP. Since the convertible truck cannot guarantee whether Apple is stolen or transferred on the transmission path, how much goods will eventually arrive at the destination depends on the mood