I've never touched a network, so I don't know - "IP network" super introduction for the cloud generation: basic network knowledge in the cloud era learned with AWS (1)

This article is for members only. If you register as a member (free), you can see everything.

　Nowadays when the cloud and wireless LAN have become commonplace, it is becoming difficult to be conscious of the "IP network", which was previously understood physically with LAN cables, appliances, servers, etc. On the other hand, when using clouds such as IaaS (Infrastructure as a Service) and PaaS (Platform as a Service), it is necessary to understand the basics of networks, but it is still used vaguely, and failures and security It is probably related to the accident.

In this series, we will use "Amazon Web Services" (AWS) as an example of a cloud service, targeting SEs, server administrators, information systems, etc. who have not touched physical networks so far. I will explain the basic knowledge.

　A total of 7 sessions are planned, and each session will have a theme, and you will deepen your understanding while operating AWS managed services that match that theme.

In this first article in the series, we will explain the basic IP network concept and show the operation procedure of "Amazon Virtual Private Cloud" (VPC). Finally, the procedure for building the environment is also described as an "Appendix", so please refer to it if you need it.

　In order to communicate on the network, it is necessary to decide on the rules. Such rules are called "protocols" in the network world. Various protocols have been created so far, but the one that is now widely used is "Internet Protocol", which is abbreviated as "IP". Currently, this IP is mainly "IPv4" of Version 4, but "IPv6", which is the updated version of Version 6, is also used.

　I think that you usually specify the name and address of the person you are sending the item to. Even in the computer world, information that specifies the name and location of the other party is necessary when communicating with each other. "IP address" is the specific information assigned to communication terminals such as computers in order to communicate with IPv4 and IPv6.

　This IP address consists of 32 bits for IPv4 and 128 bits for IPv6. increase. Therefore, there are 2³² = 4,294,967,296 IPv4 addresses, and 2¹²⁸ = approximately 3.4 x 10³⁸ addresses for IPv6 addresses. exists. However, since bit (binary) numbers are difficult for humans to handle, IPv4 addresses are formed by converting four numbers (0 to 255) into decimal numbers for each 8 bits and separating them with a "." (period). Expressed as 8 numbers (0 to FFFF) converted to hexadecimal for each 16 bits and separated by a colon (:). Since the IPv6 address is very long, you can omit the place where 0 continues with "::" (two colons), although there is only one place.

From this point on, IPv4 will be explained in this paper, but the basic concept is the same for IPv6.

　In the IPv4 address, each of the four decimal numbers is called an "octet", and from front to back they are called "1st octet", "2nd octet", "3rd octet" and "4th octet". For "192.168.1.10", "1st octet is 192, 4th octet is 10".

　By assigning different IP addresses to multiple communication terminals, each terminal can specify the communication partner and communicate. If you have a network where terminals are directly connected to each other or a very small network that only connects a few units with a concentrator such as a "hub" or "switch" in between, communication is possible with this, but for networks beyond that Identifying the location of the other party is difficult and not realistic.

　Construct a network with a relay device called a "router" between them, and perform "routing" processing to enable communication between terminals Become.

In routing, IP addresses are not simply treated as one address , the first half is the "network part" and the second half is the "host part". In addition, a value called "subnet mask" is used to specify the part to be divided.

　The subnet mask is a 32-bit value like the IP address, and in binary notation it is a value followed by 0 after 1 (*1). The part corresponding to 1 in the subnet mask of the IP address is the network part, and the part corresponding to 0 is the host part.

*1: Initially, networks were classified as classes A to E based on the value of the first 3 bits of the IP address (classful), but currently, networks are classified according to any size using subnet masks. (classless) is used.

　Only the address of this network part is extracted, and the address with all bits in the host part set to 0 is the "network address", and the address with all bits in the host part set to 1 is the "broadcast address". "It's called. Each of these values ​​is an address indicating a network (subnet), an address used for communication sent to all terminals in the network, and not an address assigned to each terminal.

　For example, there is an IP address "192.168.1.10", and this subnet mask is "255.255.255.0". In this case, the first to third octets are the network part (the network address is "192.168.1.0"), and the fourth octet is the host part (10). The broadcast address is "192.168.1.255".

　In addition to the subnet mask, there is a value called "prefix" that indicates the boundary between the network part and the host part. The prefix is ​​the number of 1s in the subnet mask as it is, and is written in the form of "/" (slash) and the prefix following the IP address. If the subnet mask of the IP address "10.0.0.1" is "255.0.0.0", 255 is a binary number with eight 1's, so it is written as "10.0.0.1/8".

　In an environment where each terminal is located far away, a router is introduced as a relay device, and the destination network is specified and communicated through routing processing. For this reason, routers are used to determine which port (interface) each network (subnet) is to go to, or which next hop (the next router to send to the destination terminal to communicate, learned by IP address). Is it ahead" is statically (static = manually) registered.

Alternatively, collect dynamically (dynamically = automatically) using a function called "routing protocol" and create a list of route information called "routing table".