Subnetting, IP addressing, Netmasks, and broadcast addresses

This is the basic information you are going to need to memorize to UNDERSTAND subnetting. Without being able to distinguish a class A,B,C and Now D (multicast) and E (anycast--still experimental) you cannot possible understand any further.

This is not real hard people! It takes very little work to do this. Once you have a handle on what the defaults are for the different IP classes go to my Simply Subnetting Page.

Example Ip addresses with no subnetting

Class	Most significant octet	Network bits	Host bits	example ip addresses	Netmask	Broadcast
A	0-127	8	24	85.110.43.7	255.0.0.0	85.255.255.255
B	128-191	16	16	132.65.20.109	255.255.0.0	132.65.255.255
C	192.223	24	8	210.20.210.20	255.255.255.0	210.20.210.255

Class A addresses begin with 0xxx, or 1 to 126 decimal
Class B addresses begin with 10xx, or 128 to 191 decimal
Class C addresses begin with 110x, or 192 to 223 decimal
Class D addresses begin with 1110, or 224 to 239 decimal (multicast)
Class E addresses begin with 1111, or 240-254 decimal (anycast)

Addresses beginning with 01111111, or 127 decimal, are reserved for loopback and for internal testing on a local machine. [You can test your NIC by pinging 127.0.0.1 which will always point to your machine]. Class D addresses are reserved for Multicasting and class E addresses are reserved for future use [anycast--IPV6]. Class D and E should never be used for host addresses.

Calculating the number of networks available

Class	Total available Networks	Nodes per Network
A	2 ^7 –2 = 126	2^24 – 2 = 16,777,214
B	2^14 – 2 = 16,382	2^16 – 2 = 65,534
C	2^21 – 2 = 2,097,150	2^8 – 2 = 254

Because neither the network address, the subnet address, nor the host address can have the binary value of all zeros or all ones, there are always two fewer networks and two fewer nodes than the binary maximum.

Table for converting decimal to Binary

When determining subnet, netmask, and broadcast addresses, remember this:

1.Convert the IP address to binary

2. Enter the netmask in binary-------enter a 1 in each network and subnet address bit, and a zero for each host address bit--- this can also help you determine how many bits are set for the subnet and how many for the host.

3. Enter the broadcast address in binary-----enter a one in each host address bit; then copy each network and subnet bit into the corresponding broadcast address fields.

I know, the broadcast thing confuses hell out of me too. I am currently working on an easier way of explaining that one. If anyone has any suggestions please email me.

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