The Network: Principle

Infrastructure¶

First of all, what is a network?

In its most elementary version, a network consists of two devices connected to each other, by a network cable for example.

The important point here is that a device connected to the network must have a network interface, a component capable of communicating, i.e., sending and receiving a signal.

For example, your laptop has two network interfaces: the RJ45 port and the wifi card. The signal that passes through the network interface is a binary signal.

Small parenthesis¶

Supercomputer: a peer-to-peer model¶

High Performance Computing¶

At the level of each subdomain:

• Distributed algebraic operations

• Resolution of local problems (DD solvers)

but let’s close the parenthesis, we’re not here to talk about HPC but about networks!

Different network qualities¶

Network quality, a little thing that matters depending on the application 🚀

Generally we talk about three qualities:

• Bandwidth: the amount of data that can be transmitted per unit of time (in bits per second, bps)

• Latency: the time needed for a data packet to reach its destination

• Reliability: the probability that data is transmitted without error

OSI Model¶

Open System Interconnexion

Standard established
by the ISO committee in 1984

Objectives:

standardize communications
between devices on a network

Addressing¶

This address can be temporary or fixed.

This is what we call the IP address, for Internet Protocol. The IP address of a network interface is written as a combination of four numbers between 0 and 255.

so there are two parts: the network address (often on 24 bits) and the host address (often on 8 bits) when we need to write the address of a network we write it like this the number of bits of the network address

IPv6 Addresses¶

in 2011 we predict the exhaustion 💣 of available IP addresses!...

2³² = 4,294,967,296 that is about 1/2 address per person on earth
(of course some people have more than others 😅)

Therefore the IPv6 protocol was implemented (the old protocol was v4)

The principle is simple: go from an address on 32 bits to an address on 128 bits
for example (in hex) 2001:0db8:0000:85a3:0000:0000:ac1f:8001
In fact we have so many addresses that we can give an IP address to every grain of sand on earth 🏖 ️

Currently deployed but partially - mainly, but not only, in the network core at operators

And why not everywhere, you might ask?
well notably, the need for IPv6 is less important than expected thanks notably to NAT
we’ll talk about it again...

Interconnection¶

Local network¶

Remote network¶

To summarize:¶

manages three elements:

• Routing

  path between two machines in different networks,
  path passing through gateways (routers)
  these famous machines having interfaces in two distinct networks.

• Relaying

  takes care, once the route is determined,
  of transmitting the information from machine A to machine B

• Flow control

  an optional but nevertheless essential functionality
  which allows to decongest the entire network (in the broad sense).
  A bit like Waze for data transit

By the way: what is my IP?¶

import requests

response = requests.get("https://api64.ipify.org?format=json")
public_ip = response.json()["ip"]

print("Public IP:", public_ip)

import socket

def get_outgoing_ip():
    with socket.create_connection(("8.8.8.8", 53)) as s:
        return s.getsockname()[0]

print("Outgoing IP:", get_outgoing_ip())

1
2
$ python my-public-ip.py
Public IP: 138.96.202.10

1
2
$ python my-local-ip.py
Outgoing IP: 10.1.1.15

(*) from the terminal, use: ipconfig on Windows, ifconfig on MacOS, ip address show on Linux

NAT (Network Address Translation)¶

Domain names in all this!¶

Remembering IP addresses is still not super 🤯!

(*) this is the IP address of the server that hosts OASIS

--

For this in the Internet infrastructure there is a magic thing, the:

Basically it’s the service that makes the association between a domain name and an IP address.

DNS from the terminal¶

# several utilities to make DNS queries

$ nslookup oasis.minesparis.psl.eu
Server:		192.168.0.1
Address:	192.168.0.1#53

Non-authoritative answer:
Name:	oasis.minesparis.psl.eu
*Address: 91.134.82.158

$ host oasis.minesparis.psl.eu
*oasis.minesparis.psl.eu has address 91.134.82.158

$ dig @8.8.8.8 oasis.minesparis.psl.eu A +noall +answer

; <<>> DiG 9.10.6 <<>> @8.8.8.8 oasis.minesparis.psl.eu A +noall +answer
; (1 server found)
;; global options: +cmd
*oasis.minesparis.psl.eu. 161	IN	A	91.134.82.158