The Diary of a SysAdmin

I think it is better to tell the difference of Subnet Mask and Variable Length Subnet Mask(VLSM) at the beginning. As I discuss in earlier article Subnet Mask is there to split one IP address into several IP’s which can use in difference LAN’s. But the question is it limit the number of accessible hosts(computers) in each LAN.  Let takes the previous example,  192.168.5.0/26 (LAN A) can only have 62 (2^6 -2) computers(hosts). But Imagine that we need to keep 100 computers in LAB A? Now I think you can understand how Subnet Mask is questioned. The answer is Variable Length Subnet Mask. I try to discuss how we use VLSM in practice in this article. I rearrange the previous example as following. ISP given address -> 192.168.5.0 /24 LAN A -> 100  (lets think LAN A need 100 computers). LAN B ->50 LAN C -> 50 LAN D ->50 Let see how we solve this problem. 192.168.5.0 /24 is the given IP and we take one bit from host side of that IP. We can define two different IP’s b

Imagine that you need to make four different networks(LAN’s). Then you ask form ISP(Internet Service Provider) to four different IP’s. But each of network has less than 20 computers. So ISP will say we cannot give four IP’s and we give you one IP and Split it into four difference networks. Let see how we done it. ISP given network address: 192.168.5.0 255.255.255.0                                                                                                                                  The number of networks that we have : 4 (2^2) 192.168.5. 00 000000        (we take two bits from available host’s bits because we need four different networks).       0     0     0   0   0  0  0   0        (consider last 8 bits) 128  64  32 16  8  4  2   1 00  -> 192.168.5.0       LAN A                                01 -> 192.168.5.64      LAN B 10 ->192.168.5.128     LAN C 11 ->192.168.5.192      LAN D LAN Name Network Address Broadcast Address Host’s IP Range