{"id":2751,"date":"2019-06-01T20:54:10","date_gmt":"2019-06-01T18:54:10","guid":{"rendered":"http:\/\/miro.borodziuk.eu\/?p=2751"},"modified":"2019-08-30T05:45:14","modified_gmt":"2019-08-30T03:45:14","slug":"network-fundamentals","status":"publish","type":"post","link":"http:\/\/miro.borodziuk.eu\/index.php\/2019\/06\/01\/network-fundamentals\/","title":{"rendered":"Network Fundamentals"},"content":{"rendered":"

The Open Systems Interconnection (OSI) Model is a standard used by networking manufacturers globally. It was created and published in 1984; it splits all network communications into seven layers. Each layer serves the layer that’s above it plus the layer beneath it which adds additional capabilities.<\/p>\n

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Data between two devices travels down the stack on the device’s A-side (wrapped at each layer) and gets transmitted before moving up the stack at the devices B-side (where the wrapping gets stripped away at every stage). This data wrapping process is called encapsulation.<\/p>\n

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At Layer 1<\/span> (Physical), networks use a shared medium where devices can transmit signals and listen.
\nLayer 1 showcases how data gets received and transmitted while taking into consideration the medium, voltages, and RF details.<\/p>\n

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IPv4 addresses<\/span> are how two devices can communicate at layer 4 and above of the 051 seven-layer model. IP addresses (IPs) are actually 32-bit binary values but are represented in dotted-decimal notation to make them easier for humans to read and understand.<\/p>\n

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Subnetting<\/span> is a process of breaking a network down into smaller subnetworks. You might be allocated a public range for your business or decide on a private range for a VPC. Subnetting allows you to break it into smaller allocations for use in smaller networks (e.g., VPC subnets).
\nIf you pick 10.0.0.0\/16 for your VPC, it’s a single network from 10.0.0.0 to 10.0.255.255 and offers 65,536 addresses. That VPC could have a single subnet within it that’s also 10.0.0.0\/16.<\/p>\n

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\nWith a certain size of VPC, increasing the prefix creates two smaller networks. Increasing again creates four even smaller networks. Increasing again creates eight even smaller \u2014 and so on.<\/p>\n

You won’t need to know this from memory \u2014 there are plenty of cheat sheets available to help you along the way.<\/p>\n

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Local device-to-device communication<\/span> takes place using Ll (Physical) and L2 (Data Link) using MAC addresses and physical 0’s and I ‘s. This doesn’t scale across LANs, so a method of network-to-network transit is needed. IP routing provides this. The method used depends on if the two devices are local, in a known remote network, or in an unknown network.<\/p>\n

IP-to-IP communication that occurs locally doesn’t use a router. ARP is used to find the MAC address for the destination IP address. The IP packet is created at L3 and passed to L2, where it’s encapsulated inside an ethernet (L2) frame. The frame is sent to the destination MAC address. Once received, the L2 frame is removed and the IP packet is passed to L3.<\/p>\n

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\nIf Instance A wants to communicate with Instance B, it can use its IP and subnet mask to determine if B is local. If it’s not, then the following process occurs:<\/p>\n