Vlsm

In class he did variable length subnet masks. What is it and how does one do sums with it?

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What resources are you using to study for your cisco?

I'm using Todd Lammle's book and video series on IT Pro TV, he explains it quite well.

wonder[riya7

I got the book. How long will it take to read the book?

Welly_59

Less time if you actually started rather than asking

CryptoQue

wonder[riya7 VLSM is used to scale standard subnets (i.e. Class C) to fit network requirements. For example, if you're redesigning a network for a company that has 3 departments they want to keep isolated. Department 1 (HR) has 105 computers, department 2 (Finance) has 40 computers, and department 3 (Public Relations) has 55 computers. The company currently has all departments configured on a 192.168.1.0/24 network. You can use VLSM to meet the company's needs. You would breakdown the class C into smaller subnets that are comparable to the amount of hosts that will be connected.

Network Subnet = 192.168.1.0/24
HR = 105 computers = /25 = 126 usable IPs
Finance = 40 computers = /26 = 62 usable IPs <---couldn't use a /27 because the maximum usable IPs for it is only 30
Public Relations = 55 computers = 62 usable IPs

New Networks
HR = 192.168.1.0/25
Finance = 192.168.1.128/26
Public Relations = 192.168.1.192/26

New IP Ranges
HR = 192.168.1.1 - 192.168.1.126
Finance = 192.168.1.129 - 192.168.1.190
Public Relations = 192.168.1.193 - 192.168.1.254

*routing will need to be involved in this process, but that's a more detailed topic you can find a lot of research on.