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Netmask
A Netmask is a 32-bit "mask" used to divide an IP address into subnets and specify the network's available hosts. In a netmask, two bits are always automatically assigned. For example, in 255.255. 225.0, "0" is the assigned network address.
Router Address
Your router IP is your identification number for whatever device is connected to your network
Look at the New Subnet Increment (which is used to find the next Network Address) and The Examples!
CIDR Table
| Subnet Mask | CIDR Prefix | Total IP's | Usable IP's | Number of Class C networks |
|---|---|---|---|---|
| 255.255.255.255 | /32 | 1 | 1 | 1/256th |
| 255.255.255.254 | /31 | 2 | 0 | 1/128th |
| 255.255.255.252 | /30 | 4 | 2 | 1/64th |
| 255.255.255.248 | /29 | 8 | 6 | 1/32nd |
| 255.255.255.240 | /28 | 16 | 14 | 1/16th |
| 255.255.255.224 | /27 | 32 | 30 | 1/8th |
| 255.255.255.192 | /26 | 64 | 62 | 1/4th |
| 255.255.255.128 | /25 | 128 | 126 | 1 half |
| 255.255.255.0 | /24 | 256 | 254 | 1 |
| 255.255.254.0 | /23 | 512 | 510 | 2 |
| 255.255.252.0 | /22 | 1024 | 1022 | 4 |
| 255.255.248.0 | /21 | 2048 | 2046 | 8 |
| 255.255.240.0 | /20 | 4096 | 4094 | 16 |
| 255.255.224.0 | /19 | 8192 | 8190 | 32 |
| 255.255.192.0 | /18 | 16,384 | 16,382 | 64 |
| 255.255.128.0 | /17 | 32,768 | 32,766 | 128 |
| 255.255.0.0 | /16 | 65,536 | 65,534 | 256 |
| 255.254.0.0 | /15 | 131,072 | 131,070 | 512 |
| 255.252.0.0 | /14 | 262,144 | 262,142 | 1024 |
| 255.248.0.0 | /13 | 524,288 | 524,286 | 2048 |
| 255.240.0.0 | /12 | 1,048,576 | 1,048,574 | 4096 |
| 255.224.0.0 | /11 | 2,097,152 | 2,097,150 | 8192 |
| 255.192.0.0 | /10 | 4,194,304 | 4,194,302 | 16,384 |
| 255.128.0.0 | /9 | 8,388,608 | 8,388,606 | 32,768 |
| 255.0.0.0 | /8 | 16,777,216 | 16,777,214 | 65,536 |
| 254.0.0.0 | /7 | 33,554,432 | 33,554,430 | 131,072 |
| 252.0.0.0 | /6 | 67,108,864 | 67,108,862 | 262,144 |
| 248.0.0.0 | /5 | 134,217,728 | 134,217,726 | 1,048,576 |
| 240.0.0.0 | /4 | 268,435,456 | 268,435,454 | 2,097,152 |
| 224.0.0.0 | /3 | 536,870,912 | 536,870,910 | 4,194,304 |
| 192.0.0.0 | /2 | 1,073,741,824 | 1,073,741,822 | 8,388,608 |
| 128.0.0.0 | /1 | 2,147,483,648 | 2,147,483,646 | 16,777,216 |
| 0.0.0.0 | /0 | 4,294,967,296 | 4,294,967,294 | 33,554,432 |
The CIDR number comes from the number of 1's in the subnet mask when converted to binary.
The common subnet mask 255.255.255.0 is 11111111.11111111.11111111.00000000 in binary. This adds up to 24 1's, or /24 (pronounced 'slash twenty four').
A subnet mask of 255.255.255.192 is 11111111.11111111.11111111.11000000 in binary, or 26 1's, hence a /26.
And so on...
254 decimal to binary conversion Can convert the other way too
Determining the Subnet(Net) ID and Host ID
First, we need to convert the IP address and subnet mask to binary. The following figure shows a binary representation of 192.168.1.50 with a subnet mask of 255.255.255.0:
Next, we perform a bitwise AND operation between the IP address and the subnet mask:
Therefore, the resulting binary number is the subnet ID (11000000.10101000.00000001.00000000), which we need to convert back to decimal form.
Thus 192.168.1.0 is the subnet ID and the remaining bits in the IP address (00110010) are the host ID, which we also need to convert back to decimal form: Host ID: 50. Therefore, the IP address 192.168.1.50 belongs to the network 192.168.1.0 with a host ID of 50.
EXAMPLE:
IP address: 10.0.0.55 and Subnet Mask:255.255.255.0
Therefore: Subnet ID: 10.0.0.0 and Host ID:55
IP Subnet Calculator Colocation America
IP Calculator Shows the binary
Cisco 1841 router reset password
Break Key In PuTTY
- "CTRL" + "BREAK"