Since IT-stone of note

Сиджу на робочому місці. І тут хтось позаду кричить:
— ping < моя IP-адреса>
Обертаюся й бачу: в мене летить пакет!..

DHCP

You woke up after a wild binge. Your first words "who am I?" and "where am I?". A neighbor who did not drink vodka with beer tells you all your parameters: who you are and where. This neighbor acts as a DHCP server. Be aware that there may be so-called "false DHCP servers" on the network, such as the wife - to your question "who am I?" she will give incorrect information: "you're an alcoholic, damn you." So that dynamic issuing of parameters is not always safe, it is recommended to write down your parameters (name, address, etc.) on a piece of paper.

Route for promovchuvannyam

Approach an ordinary person and ask "can you tell me how to get to the Nevmyrovych-Danchenko morgue?". There is a high probability that you will be sent to Nafig. This is the default route, in other words, if the destination address is not known, packets are sent to the default route (synonyms: default gateway, dafault gateway).

The concept of TTL

Imagine that you are 5 years old and you want to eat. You go to your father and say, "Dad, I want to eat." Your dad is watching TV, according to the routing table he sends you to mom. You go to her and ask "Mom, I want to eat". Mom is trending with her friend on the phone and according to her routing table, she sends you to your father. And so you go like a fool from dad to mom and back, back and forth, back and forth, all because crooked admins (dad and mom's parents) incorrectly configured the routing table. To protect against such situations, the concept of TTL (Time To Live) was invented, which in our situation means the amount of patience a boy has until he says "fed up" and falls at the feet of mom or dad in a helpless state. The latter, according to the rules (the standards are "so accepted in the family"), is obliged to send a short disappointing feedback to the address of the one who sent the boy to eat. This is the so-called "boy died" icmp package.

Ping

You have certainly been in a situation where you are a fool. You shout "Ostap is a fool", and in response you hear "Vasya, he is a fool". This is the simplest ping. You just pinged Ostap. Not everyone responds to pings, especially cultural ones, such as Microsoft.com, do not burden themselves with responding to your requests. It is useless to argue with such people, we know that they hear and are angry, but we cannot achieve a reaction. Still, ping is a good way to find out if a host is alive, since kicking a corpse won't get you the "I'm a fool" reaction.

Traceroute

Imagine that you live on the 9th floor and you want to know all the residents who live from you to Klavka from the 3rd. You take an explosive package and, based on the formula of free fall, calculate the time of the explosion of the package above the 8th floor. This is TTL=1. After the package explodes, the ferocious peak of the neighbor from the 8th floor will appear. The reaction time depends on the server load, that is, on the occupation of the neighbor and on the shapes, that is, whether the system is in the air, or you live on a planet where the atmosphere is liquid nitrogen. Well, if you don't wait for an answer at all - your neighbor is deaf - he has banned icmp replies, or he banned them only for you if he is already tired of your tricks and has learned to ignore you. Next, set TTL=2, etc. Do not forget that if Klavka lives above you, it is No route to host

Access control list

For several weeks, you walked around the district, at the right moments you turned a blind eye to the arbitrariness of the administrators and did not complain to the administration (cops). They decided to invite you to get drunk together. On it, you accidentally drank a liter of vodka, smoked a stack of hay, watched the carpet in the corridor and beat two guards in the store. The athletes were impressed and accepted into their team, adding your name to the "access control list". Thus, you have passed the so-called authorization procedure.

Public-key cryptography

A month later, you were pulled over by cops while driving a scrap car. And they began to demand documents for a wheelbarrow. You began to tell them a tearful story about the fact that this car is your half-brother's, and you forgot the documents for it at home. This is called encoding. Something like "coding from alcoholism", only in this case the representatives of the authorities act as bad spirits. As a confirmation of your words, you offer them all your money, as well as the car key, so that they can return the car and record this return of the vehicle in the list of solved crimes. This process is called public-key cryptography and its effectiveness depends on whether you were able to guess the level of the policemen's internal needs for fame and money.

DHCP Relay Agent

You wake up after a wild binge on someone else's couch. Nearby, instead of the woman with whom you danced and seemed to kiss yesterday, an unknown unshaven man is snoring. You shout in his ear: "Who am I? Where am I?!" He squints his eyes with difficulty, looks around in surprise and, since this question bothers him no less than you, he goes in search of the owner of the dacha.

POP3

You walk over to your rusted mailbox on the entryway wall, open the door, and, groping, pull out a pile of free newspapers and advertising waste. Going up the elevator to your floor, you enjoy to your heart's content offers to glaze the loggia and do a pedicure, approach the garbage chute and take everything down there, without noticing among all the letter from grandmother about the death of grandfather. The next day, the box is even more clogged, but you can't open it, because the tightly packed waste paper has pressed the lock tab - this is the response "-ERR Account is over-quota" after an authorization attempt.