The Internet (Week 11) Flashcards

1
Q

What is the Internet?

A

The Internet is a “network of networks”

A loose, unstructured, ad hoc, chaotic collection of networks, all connected to each other => interconnected networks

These subnetworks might be large, small, corporate, government, private, educational, etc. networks

Each network can have its own network rules and protocols or different types of hardware

To be part of the Internet, individual networks just must support Internet Protocols on top of existing communication mechanisms

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2
Q

What are Communication Protocols?

A

A large set of protocols define how the Internet works

A communication protocol is a set of rules and conventions that allow two or more parties to exchange information, e.g.
* Who can initiate the communication?
* What is the format for exchanging messages?
* What happens in case of an error (error recovery)?
* Many protocols are agreed to be technical standards

This is similar to social protocols that define how a valid interaction between multiple parties should look like, e.g., etiquette or code of behaviour

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3
Q

How did the internet start?

A

ARPANET
* Advanced Research Project Agency (Part of US Department of Defence )
* Originally, 4 university sites in the US were connected

October 29th , 1969 – 1st message sent 550 kms
* UCLA to Stanford University.
* System crashed after the letters l and o

Roughly exponential growth of number of hosts (participating computers) in 1980s and 90s

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4
Q

What does it mean that the Internet is a Reliable and Robust Web?

A

One of the original design purposes: robustness
* Make sure the network would continue to function even if major subnets fail or were destroyed

No dedicated point to point route between any two nodes

If a node/link is down (inactive) – another path is used to communicate

This property of the network is now a major challenge for some governments as it is hard to control

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5
Q

What is a Backbone Network?

A

A backbone network may be defined by the principal data routes between large, strategically interconnected computer networks and core routers on the Internet.

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6
Q

What is CANARIE?

A

CANARIE: Canadian National Research & Education Internet Backbone

CANARIE is one of the Internet Backbones in
Canada. Bandwidth on many links: 100 Gbps

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7
Q

What is the BCNET Advanced Network?

A

BC ́s part of CANARIE

connects 180+ higher education and research sites across British Columbia (including Camosun College)

9,900+ km of network connections

The weathermap shows the current traffic load (only accessible inside BCNET)
https://www.bc.net/advanced-network/traffic-map

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8
Q

What is Internet Routing?

A

We can monitor the route between network nodes with the program traceroute

Example route from a Camosun computer to the webserver of the University of Ontario Institute of Technology (www.uoit.ca) in 13 “hops”

Data is passed along from node to node until it reaches the destination

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9
Q

What is an Internet Service Provider (ISP)?

A

Internet Service Providers offer internet access for commercial or private users, e.g. Telus, Shaw, Bell, Rogers, JUCE, Lightspeed, etc.

ISPs typically operate their own networks
* Some ISPs maintain their own regional, national or even global networks
* They connect their networks (and thus their customers) via Internet Exchange Points (IXPs) to other networks

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10
Q

Internet Protocol Version 4 (IPv4) and IP Addresses

A

Any data is sent bundled in Internet Protocol (IP) packets

Every “node” of the network must have a unique ID: an IP address

An IP address (version 4, IPv4) is a 32 bit number
* 4,294,967,296 unique addresses
* Usually noted as 4 decimal numbers (8 bits each) divided by dots
* 0.0.0.0 to 255.255.255.255

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11
Q

Internet Protocol Version 6 (IPv6)

A

Next version of the internet protocol IPv6 is here (we’ve run out of available IPv4 addresses):
* Each address is a 128 bit number
Noted as 8 blocks of 4-digit hex numbers divided by colons, e.g.
http://[2607:f8b0:400a:804::200e]

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12
Q

What is Domain Name Service (DNS)?

A

Humans are not good at remembering long numbers like IP addresses
=> Domain Name System provides names that translate to IP addresses

DNS uses an hierarchical naming scheme

Example hierarchy including online.camosun.ca:

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13
Q

How does Domain Name Service (DNS) work?

A

DNS translates names into IP addresses (and the other way round)

Since 2009, DNS supports “Unicode” names, e.g. http://монголулс.icom.museum

Your computer knows at least one Domain Name Server, which it asks to translate unknown names (usually a second one is set up as backup)

ipconfig /all (Windows) and ifconfig (Mac) shows the DNS servers your computer uses

You can ask for a particular translation with nslookup [hostname] (same on Windows & Mac)
* You might be able to configure which DNS you use

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14
Q

How is a DNS query resolved, e.g. for www.camosun.ca?

A

If your computer asks for a host name unknown to your DNS server, the request is passed down the line.

  1. Ask one of the root domain servers for info about .ca
    * One out of a set of 13 highly redundant servers (those make DNS very failsafe)
  2. Ask the domain name server for TLD .ca for camosun.ca
  3. Ask the sub-domain name server for www.camosun.ca

Domain name servers keep track of recent translations to improve speed => another example of caching to improve performance

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15
Q

What are Top Level Domains (TLD) and who are they restricted to?

A

The well-known .com, .org and .net domains are open to anyone anywhere – no geographical or national limitation
* Attention: anyone can register a .com-subdomain for a couple of dollars. You may not know who you are dealing with (may be registered anonymously)

New top level domains can still be added: e.g. .biz, .museum, .web, .stockholm, .paris, are some of the “younger” TLDs, see
* e.g. https://start.stockholm/, http://hotels.berlin
* TLDs are managed by the Internet Corporation for Assigned Names and Numbers

Some top level domains are restricted to certain groups of people, e.g. .ca-domains only for Canadian citizens, Canadian companies, etc.

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16
Q

“I want my own .ca-domain name with web page and e-mail, how does it work?”

A

Check if your desired domain name is available
=> .ca-TLD is managed by Canadian Internet Registration Authority - CIRA

How much does it cost? => $ 15 to $ 20 per year (special offers possible)

What if my desired domain is not available?
=> Check out who the owner of the domain is by using a service called whois, for .ca-domains, and try to make a deal with them

How do I get a web page (and E-Mail address) for my domain?
=> domain providers typically offer such hosting services as well

How much is basic mail and web hosting (one mailbox and a simple page)?
=> $ 1 to $ 10 per month (sometimes even included in yearly domain fee)

17
Q

What is Internet Protocol Stack?

A

To reduce the complexity of a system like the Internet, a layered approach is used (remember Operating System architecture?)

These 4 layers are called the Internet Protocol Stack

A layer typically uses interfaces of services and protocols of lower layers to carry out services for upper layers

Protocols => Layer
HTTP, SMTP, SSH, etc. => Application layer
TCP, UDP, etc. =>Transport layer
IP => Network/Internet layer
Ethernet, etc. => Datalink/link layer
Electrical/light signals => Physical (hardware)

18
Q

Application Layer Protocol
What is HTTP?

A

Hypertext Transfer Protocol HTTP (and HTTP Secure - HTTPS)

Used to request information from a remote host, e.g. web pages, images, any type of file, etc.

If we put http://google.com into a browser’s address bar, it
* uses HTTP to send a request
* to the host google.com
* to a web server program
* to get the default page

19
Q

What are Ports in a Computer?

A

The idea of ports on a host computer is similar to mailboxes in a large apartment building. To receive messages from others, …
* a resident of the building uses a mailbox
* a program running on a computer
uses one or multiple ports

Programs also use ports to send messages

Port numbers are 16 bits wide, thus their range is from 0 to 65,535

20
Q

Ports for Common Services/Protocols

A

It is common that Internet services/protocols use predefined ports:

E.g. web servers listen to incoming requests on port 80 for HTTP (and on port 443 for HTTPS)

You can specify the target port of an HTTP
request in the web browser address bar

Your browser can also use other protocols,
e.g. the file transfer protocol

21
Q

Application Layer Protocol
How are Protocols used to handle Emails?

A

Several protocols are involved in the transfer of Electronic Mail:

To send out e-mail: Simple Mail Transfer Protocol (SMTP)

To retrieve e-mail from the Server hosting your Inbox:
* Internet Message Access Protocol (IMAP)
* Post Office Protocol (POP)
** Not built for using more than one mail client

If you want to send/retrieve e-mail
you have to configure your mail client
E.g.: Google Mail configuration

Protocol manages authentication, security mechanisms (like encryption) and transfer of mail messages

22
Q

Properties of Internet Protocol Packets?

A

Any data is sent over the Internet in IP packets

IP packets contain up to 65kB of data

Long messages that exceed 65kB must be broken up into smaller chunks

Each packet has a header with
* Source IP address
* Destination IP address
* Time to live counter (TTL)
* Error Check

23
Q

What is a TTL Counter?

A

Time to live counter (TTL)

TTL Counter – typically starts at value 40 and ticks down each gateway the packet passes through. This might involve 15-20 gateways.

If the count reaches ‘zero’, the packet is discarded and an error packet sent to the originator. Why might this be useful?

24
Q

TCP Handshake

A

TCP uses a “handshake” procedure to set up a connection between two hosts

To see all current TCP/UDP activities in Windows, use the command line to run the program netstat -a

25
Q

What are Private IP Addresses?

A

Some segments of IP addresses are private addresses

Routers in the public Internet only forward packets with a public IP address as source and destination address (others are discarded)

Private IP addresses can be used for private networks, e.g. local area networks at home

They are also used to overcome the shortage of public IPv4 addresses

26
Q

What is Network Address Translation (NAT)?

A

Computers with private IPs (in this example in segment 192.168.0.0 – 192.168.255.255) may use NAT to communicate with the Internet

LAN computers send their IP packets to the NAT router’s private IP address 192.168.01

The NAT router replaces private addresses in IP packets with its public address 82.10.250.19 and forwards them to the Internet

Response is processed accordingly

The outside world only sees the public IP address of the NAT router (here 82.10.250.19)