Section 7: IP Addressing

• Internet Protocol (IP) Address

  An assigned numerical label that is used to identify internet communicating devices on a computer network
• Remember, when we're dealing with two devices

  that are internal to our own network or LAN,

  we're usually going to be dealing with Layer 2 addressing,

  which is based on MAC addresses.

  And that data is going to be forward around the network

  via our network switches.

  But, once we start going to two different networks

  or even two different subnets,

  we have to start using Layer 3 addressing

  with our IP addresses.
• Now, one part of the IPv4 address

  is used to identify the network portion

  and the other part is going to be used

  to identify the host portion.
• Class A

  1st Octet: 1 - 127

  Default Subnet Mask: 255.0.0.0

  Possible Hosts: 16.7 million (256 x 256 x 256)
• Class B

  1st Octet: 128 - 191

  Default Subnet Mask: 255.255.0.0

  Possible Hosts: 65, 536 (256 x 256)
• Class C

  1st Octet: 192 - 223

  Default Subnet Mask: 255.255.255.0

  Number of IPs: 256
• Class D

  1st Octet: 224 - 239

  Does not have a subnet mask

  Class D addresses are special, they are reserved for multicasting or multicast routing
• Multicast Address

  A logical identifier for a group of hosts in a computer network
• A multicast address is like a group chat

  The group chat name is the multicast address

  When you send a message to that group chat name - all of the members of that group get a copy of that message
• Class E

  1st Octet: 240 - 255

  No default subnet mask

  Reserved for experimental purposes - research and development only

  Contains 268 million addresses reserved for future use
• When both the first octet of an IP and the default subnet mask match the same class this is referred to as a classful mask

  
  

  Example: 192.168.1.4 with a mask of 255.255.255.0 both are class C
• Classful Mask

  The default subnet mask for a given class of IP addresses
• We often, instead, want to break down these large networks

  into smaller networks.

  To do this, we're going to use a process known as subnetting.
• Classless Inter-Domain Routing

  Allows for the borrowing of some of those host bits and reassigning them to the network portion
• Subnetting

  Allows for the use of a classless subnet mask to create smaller networks with fewer hosts in each network
• CIDR Notation (sounds liker CIDER)

  Abbreviating IP addresses with / slash notations

  Example

  192.168.1.4 with subnet mask of 255.255.255.0 would be rewritten as

  192.168.1.4 /24
• CIDR Notations for classful masks

  Class A: /8

  Class B: /16

  Class C: /24
• Types of IPs: Public (Routable)

  Can be accessed over the Internet and is assigned to the network by an ISP
• The global entity that manages and leases publicly routable IP addresses is the Internet Corporation for Assigned Names and Numbers (ICANN)
• ICANN Entities Globally

  ARIN - North America

  LACNIC - Latin America

  AFNIC - Africa

  APNIC - Asia Pacific

  RIPE - Europe

  
  

  These parts of ICANN are way too busy to sell individual IPs and will only bother selling a whole bunch
• ISPs will sell you individual public IPs
• Types of IPs: Private (Non Routable)

  Can be used by anyone any time but only within their own local area network
• Private IP ranges include those that start with either

  10

  172

  or 192
• Network Address Translation (NAT) allows for routing of private IPs through a public IP
• The document used to defined how organizations could conduct address allocations for private Intranets is known as RFC 1918

  
  

  RFC meaning request for comments
• IPs allowable by class for private IPs: Class A

  Starting value: 10

  IP Range: 10.0.0.0 - 10.255.255. 255

  Possible Hosts: 16.7 million (256x256x256)
• IPs allowable by class for private IPs: Class B

  Starting value: 172. 16 - 172. 31

  IP Range: 172.16.0.0 - 172.31.255.255

  Possible Hosts: 1.05 million (16x256x256)
• IPs allowable by class for private IPs: Class C

  Starting value: 192. 168

  IP Range: 192.168.0.0 - 192.168.255. 255

  Possible Hosts: 65,536 (256x256)
• Be especially careful when an IP starts with 172 because the only way it is private is if the 2nd octet is between 16 and 31
• Special IP Addresses: Loopback Address (127.0.0.1)

  Creates a loopback to the host and is often used in troubleshooting and testing network protocols on a system

  
  

  This allows any higher level protocol

  to send data to the host itself

  without actually going out to a switch or a router.
• Special IP Addresses: Automatic Private IP Addresses (APIPA)

  Used when a device does not have a static IP address or cannot reach a DHCP server

  
  

  Always start with 169.254
• Without APIPA addresses, if a system could not get an address over DHCP it would eventually just crash after trying over and over
• Virtual IP Address (VIP or VIPA)


  An IP address that does not correlate to an actual physical network interface

  
  

  Usually used for network address translation (NAT)

  
  

  Fault tolerance

  
  

  Virtualization
• Routers often use virtual IP addresses to provide redundancy in their connectivity options

  By having a single virtual IP

  assigned to the default gateway, for example,

  we can have multiple routers

  that could answer up on behalf of that virtual IP.

  This would allow us to have a primary device

  to use during normal conditions

  and an alternate device that could be used

  when the primary device fails.
• Subinterfaces

  A virtual interface that is created by dividing up one physical interface into multiple logical interfaces
• Virtual IPs go hand in hand with subinterfaces because each virtual interface is going to be able to assigned a virtual IP address
• Methods of Data Transfer over IPv4: Unicast

  Data travels from a single source device to a single destination device
• Methods of Data Transfer over IPv4: Multicast

  Data travels from a single source device to multiple (but specific) destination devices
• Methods of Data Transfer over IPv4: Broadcast

  Data travels from a single source device to all devices on a destination network
• Broadcast vs Multicast

  Broadcast is EVERYBODY

  Multicast is only those opted to get it