June 26, 2019
IPv4 address are 32bit with an octet each consisting of 8 bits (hence the 255.255.255.255 limit).
- Leading 0s can be compressed
- Groups of zeroes can be removed (once) and represented by
Example of an
2001:0DB8:AC10:FE01:0000:0000:0000:0000 which can be further compressed to be represented as
The main advantage of IPv6 over IPv4 is the larger address space.
Each segment is represented by 16 bits.
Media Access Control (MAC) Address
- Within range to max address
- 48 bit address.
- First three sections represent the Organizationally Unique Identifier (OUI) - number deontes the manufacturer and whether this is a
- The MAC addresses are mapped to IP addresses through the
Address Resolution Protocol (ARP).
Address Resolution Protocol (ARP)
When requestion a resolution to an address, a member of the LAN network sends out a broadcast on the network to all devices asking for a
Target IP but no
Target MAC address.
The device with the
Target IP would then respond with a Unicast to the original device provide the
Target MAC address that was requested..
- Broadcast => who has IP 192.168.1.212? No
TargetMAC address as it is a broadcast
- Unicast back => I have the IP 192.168.1.212. Has all
Designates which sections of the IP address apply to the network, and which apply to the host.
192.168.001.101 we could have Network Portion
255.255.255 and Host Portion
.101. Only the
101 part of this address is the host portion, so in the above case we know the network is
192.168.001. The network mask determines the network size and
In this example the
192.168.001.0 - 192.168.001.255.
Note that in a classful network, the
.0 is not a valid IP as it represents a network.
The highest IP in the range isn’t used for host assignment as it is consider the
broadcast IP for broadcasting a packet to an entire IPv4 subnet.
broadcast address also cannot be an even number.
Common network masks include
255.0.0.0 where the 255s represent the network portion and the 0s represent the host portion. The are also the submasks of the
A, B and C networks.
network portion means we can have many networks.
host portion defines how many devices or how many portions you can have on your LAN. This is the only part of the address on a LAN that changes.
Calculating Subnet Hosts
2^n - 2 where n is the number of host bits.
We subtract 2 addresses for the host ID and the broadcast.
Calculating Subnet Range
We take an IP address and the subnet mask and use an AND calculation on their respective binary representations to figure out the initial IP in the range.
192.168.100.200 => 11000000 10101000 01100100 11001000 255.255.255.224 => 11111111 11111111 11111111 11100000 (2^5 = 32) ============================================================== 11000000 10101000 01100100 11000000 192.168.100.192 32 addressess = 224 Network Address: 192.168.100.192 Broadcast Address: 192.168.100.223
2^b / n+2 where:
- b: number of bits in the host portion
- n: number of hosts per subnet
CIDR -> Classless Inter-Domain Routing
This is a replacement for classful networking.
- does no use classes for network assignment or sizing
- entire unicast range (0-233 in first octet) can be segmented into any sized network
- subnet masks not limited to
CIDR blocks are denoted with an IP address followed by a
/n where n is a number between 0 and 32 that notes the side of the
192.168.100.1/24 would be a network that supports 256 host addresses (the last octet).
192.168.100.1/23 would support 512 host addresses and so on and so forth.
A personal blog on all things of interest. Written by Dennis O'Keeffe, Follow me on Twitter