Tag: IP

IP Subnetting

When Classful addressing is used an ENTIRE class A, B, or C network is needed for each individual network segment.  Here is an example of a network using classful addressing, notice that this can lead to a severely inefficient method of allocating IP address space:


The more reasonable option would be to reserve a single classful IP Network and use subnetting to break it up into three parts for this network instead.  This will allow for more efficient use of the IP address space given.

When subnetting, IP addresses are broken down into three parts:

  • Network
  • Subnet
  • Host


This shows  the benefits to subnetting, essentially more efficiently using IP address space to preserve as many addresses as you can from what you’ve been allocated.

Here are some facts related to the format of an IP Address:

  • If the subnet has been defined with y host bits, there are 2y-2 valid usable IP addresses in that subnet, two of the numeric values are reserved
  • The first reserved address is the subnet number itself, this number has all binary 0s in the host bits
  • The second reserved number is the broadcast address, which has all 1’s in the host bits.
  • When doing classful subnetting if the subnet mask has x subnet bits then 2x possible subnets exist for that classful network.
  • Two subnet numbers, the highest and the lowest are discouraged from use:
    • Zero subnet: this is the subnet field that has all binary 0s, each zero subnet is the same as the classful network number
    • Broadcast Subnet: the subnet field with all binary 1`s same as the network broadcast address

How to find the subnet number and valid range of IP addresses – Binary

the range of valid IP addresses in a subnet begins with the IP that is 1 larger than the subnet number itself, it ends with the IP address that is 1 smaller than the broadcast address for the subnet.  So to find the valid range of addresses just calculate the subnet number and broadcast address:

  • To derive the subnet number, perform a bitwise Boolean AND between the IP address and subnet mask
  • To derive the broadcast address, change all the host bits in the subnet number from 0s to 1s

a bitwise Boolean AND means that you line the binary version of the address and the subnet on top of each other, and then AND the two bits that line up vertically.

  • Result = 1 if both bits are 1
  • Otherwise the result = 0


So given the output above the Subnet Number is and the broadcast address is  So the valid range of IP addresses is: –



IP Protocol: IP Addressing

Computers and networking devices use IP addresses like a home address with the postal service.  In order for it to send and receive data it must be given a unique address other devices can use to send data to it….just like mail that’s sent to your unique home address.

Here are a few rules to IP Addressing that should be known:

  • IP addresses are 32 bit binary numbers
  • Usually IP addresses are written in dotted decimal notation with each decimal octet representing 8 bits.
  • IP Addresses are assigned to network interfaces
  • Computers with an IP address are also referred to as IP hosts.
  • Groups of IP hosts not separated from each other by a router are in the same grouping.
  • These groupings are referred to networks, subnets, or prefixes
  • IP hosts separated from other IP hosts by a router MUST be in separate networks.

IP addresses are considered classful or classless.

Classful IP addresses mean that the main class A, B, C rules from RFC791 are considered.  Class A,B and C networks are identified by their first several bits or by the range of decimal values in the first octet.

Classful IP addresses also consist of two parts, a network and a host part.  The size of the network is defined by  the class of the network.classful

Classless IP addressing means that class A, B, and C rules are ignored.  Each IP address is also seen as two parts called the prefix and host parts of the address.

the prefix defines how many beginning bits of an IP address identify the network.  All hosts with the same prefix are in the same network and can be called a  subnet or prefix.

Prefix’s must be listed with a prefix length, the prefix length is a decimal number that defines the length of the prefix.  For example a prefix ending with a /24, means that there are 24 bits used in the subnet mask….meaning you can derive the prefix length from how many active ‘1’s are turned on in the subnet mask’s bits.


Transmission Control Protocol (TCP)

TCP is the protocol that ensures reliable transport delivery when used together with the IP protocol.  Other duties TCP performs is the operation of ensuring packets are maintained in the right order, and that delay is kept to a minimum level.  TCP also prevents packets from being duplicated, to ensure that all data received is consistent, in order, complete, and smooth.

TCP is in the transport layer of the OSI model, so it applies its functions to packets before they’re passed on to the IP layer. TCP will put datagrams into TCP packets before sending to the IP layer where they’re encapsulated into IP packets.  Data that is broken is is done so into bits placed into packets then transferred over the network.  Once the packet reaches it’s destination the bits are reassembled into the original piece of Data.


IP Protocol

The IP Protocol standardizes how machines forward or route packets over the internet or any IP network based on the IP address.  The most fundamental piece to this protocol is it’s ability to perform routing functions to forward packets appropriately to various destinations.  The ability to route packets and define the standards for which a packet is addressed and made unique so it can be routed appropriately is only a single component to allow for the delivery of packets.  For instance IP does not have any measures on it’s own for reliable packet delivery, so the IP protocol itself must work with other protocols to achieve reliable packet delivery, such as TCP.