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Networking

Explaining how the internet works.

• IP Address
  • IP Address Classes
  • RFC1918
    • Private IP Addresses
    • NAT
  • IPv6
• Ports
• TCP and UDP
• Modem, Router, Switch, and Repeater
• MAC Address
• Forward proxy, reverse proxy, and VPNs
• URLs
• DNS
• SSL and TLS
• Content delivery networksCDNs

IP Address

IP Addresses are unique address that allow a device to communicate using Internet Protocol.

IP Addresses are composed of 4 octets which are separated by periods. Each octet can range from a value of 0 to 255.

The Subnet Mask/Netmask/Mask is used to identify which IP Addresses are part of the same network or not.

Ex: IP Address: 192.168.1.204 Subnet Mask: 255.255.255.0

This means that any IP Addresses starting with 192.168.1 are part of your local network. If an IP Address isn’t part of your local network then you have to talk to your router in order to connect to that IP Address.

The Default gateway/Router/Default Router is the IP Address of your router. Your device communicates with this IP Address in order to access IP Addresses that aren’t in your local network.

In your local network there are always 2 IP Addresses that have custom purposes. Network Address which is the first IP Address in your network. This is used to help other devices identify the network. Ex: 192.168.1.0 Broadcast Address which is the last IP Address in your network. When this IP Address gets something it tells every other IP Address on its local network. Ex: 192.168.1.255

IP Address Classes

• CIDR notation is just a different notation for different subnet masks

Local networks with class A IP Addresses can have 2^(8*3) different devices with their own IP Addresses. These are often reserved for large companies.

• These companies often change the default subnet mask into a smaller one to allow for more local networks. These are called classless networks. Ex: 255.0.0.0 could be changed to 255.255.255.0
• Classful networks are networks that keep the default subnet mask.

127.0.0.1 - 127.255.255.255 are loopback address. These are used to test your network by having your device call itself.

• 127.0.0.1 is often used to refer to your local devices

• Domain Name Server(DNS) is the server which converts URLs to IP Addresses.
• Dynamic Host Configuration Protocol(DHCP) is how a router assigns it’s devices an IP Address, Subnet mask, default gateway, and DNS IP address.
• Autonomous System Numbers(ASNs) are blocks of IP address purchased from ISPs. Large companies tend to use these.

RFC1918

RFC1918 was a standard in order to not run out of IP Addresses. It introduced Private IP Addresses and NAT.

Private IP Addresses

Private IP Addresses are specific IP Addresses that aren’t unique. They can be used by multiple devices, but because of that they cannot communicate directly with public IP Addresses(cannot directly connect to the internet).

Private IP Addresses are used for communication in a private network. Each device connected to the router gets its own unique private IP addresses different from all the other devices connected to the network.

NAT

Network Address Translation(NAT) is used by the router to convert your device’s private IP Address to a public IP Address which can be used on the internet.

Your router is given a public IP Address by your ISP.

IPv6

2^128 different addresses.

Often mobile devices, not connected to wifi, have IPv6 addresses.

Ports

The IP Address determines the device while the port determines which service or program on that server is to be used.

Each IP Address can have a port from 0 to 65535

Your computer temporarily assigns itself a private port during a session like when browsing the web.

A socket is a program that handles incoming and outgoing request on a specific IP address and port.

Port forwarding allows public access to sockets on a local network. It redirects network traffic from a port on a router’s public IP address ot a corresponding port on a device withing the local network.

• If you want to host a website on your local computer you need to port forward ports 80 and 443 to your server’s port.

TCP and UDP

Transmission control protocol(TCP) is used when the communication between 2 computers needs to guarantee

• the data is in order
• all the data is received

TCP establishes a connection first with a 3 way handshake.

Computer 1                   Computer 2
           -> SYN     ->
           <- SYN ACK <-
           -> ACK Received ->

User Datagram Protocol(UDP)

• doesn’t establish a connection
• doesn’t guarantee data delivery. Some data maybe lost.
• doesn’t guarantee the order of the data received
• Is faster than TCP

Modem, Router, Switch, and Repeater

Modem Converts digital signals(used by computer and router) to analog signals(sometimes used to connect to your ISP) and vice versa .

• If you don’t have any other devices in your local network you can often connect your one device to the modem.

Router given a public IP Address by your ISP and assigns private IP Addresses to each device in your local network.

• Not all routers have a separate modem.

A Switch is used for communication on a local network. It knows each devices mac address and moves any communication it gets to its corresponding mac address.

MAC Address

All devices which connect to the internet(has a network interface card) have a unique Media Access Control(MAC) Address.

An IP Address is used to local a device while a MAC address is used to identify a device.

• IP Address can change for the device, but the MAC address cannot.

Forward proxy, reverse proxy, and VPNs

A forward proxy server regulates traffic going out of a network. It is used to protect clients.

• Privacy and change location
  • Instead of using the device’s IP Address all traffic is routed through the proxy server’s IP Address. If the proxy server’s IP Address is located in a different area, when you access sites they may think you are in that different area.
• Speed and saves internet bandwidth
  • Proxy servers can cache static assets and static websites.
• Activity logging and blocking certain websites
  • Proxy servers can be set up to document what websites the clients are going to and block certain websites.

A Virtual Private Network(VPN) is like a forward proxy server, but it encrypts data that is sent over the internet and often has some guarantees of no activity logging.

A reverse proxy server regulates traffic going into a network. It is used to protect servers. A reverse proxy server is often used as a single point of entry for websites.

• Balance traffic to different servers.
• Can cache images and static sites to prevent too many unnecessary request to the servers.
• Defend against DDOS attacks by handling a lot of requests and filter out non legitimate users before they request anything from the server.

URLs

The Uniform Resource Locator(URL) is used so people can memorize words instead of IP Addresses. Typically each domain name has a corresponding IP Address. Multiple domain names can share the same IP Address.

https://www.name.net/path?param1=value1&param2=value2
[  ^   ][^] [ ^] [^]
   |     |    |   |
   |     |    | Top level Domain(TLD)
   |     | Domain
   | Sub-Domain
Protocol/Scheme(Usually determines the port)

You can buy to own domain names and top level domains together. Ex: website.com

• Once you own a domain name you can create any sub-domain you want.
• Search engines treat sub-domains as separate site while paths are treated as the same site.

What do these do? @ :

DNS

The Domain Name System(DNS) is used to figure out the IP Address of a domain name and any other associated information that the server may need to know which site you want.

Your browser has a cache for different domain name’s IP Address. DNS is only called if your browser doesn’t have a cache of that domain name

• Address(A) record maps a domain or subdomain to an IPv4 address.
• AAAA records resolve a domain or subdomain to an IPv6 address.
• Canonical(C) Name forwards a domain to another domain instead of an ip address.
  • Ex: www.example.com -> example.com
• ALIAS the same as CNAME, but can forward with the root domain name.
  • Ex: example.com -> www.example.com
• Mail Exchange(MX) is used for emails.
  • Email to name@example.com, dns checks MX for which domain the server can handle. Ex: example.com -> mail.example.com
• Text Records(TXT) used to store arbitrary data with the domain name. Like a description.
• Name Servers(NS) defines the url for the authoritative name servers. There tends to be 2 for better reliability.
  • These are typically provided by the domain registrar company.

Authoritative name servers are the last server that the DNS looks to to get the IP Address, and other information about the domain name.

SSL and TLS

Secure sockets layer(SSL) and Transport layer security(TSL) are encryption standards used for HTTPS.

SSL is older and less secure, but it is still in use.

Content delivery networks(CDNs)

Your content is on servers all around the world in order to reduce delay times for your users.