I'm a web developer interested in learning network. I work on Windows platform. Many of my friends and colleagures believe that to learn netwrok, I should become familiar with Linux platform. Should I? I mean, can't I learn network and it's concepts thoroughly on Windows Server platform?
Network terminology and concepts should be fairly OS agnostic. Though linux may help you get a better understanding of network concepts, this will probably be due to the fact that you will have to have some basic networking knowledge to set up a linux server (depending on the distribution). So basically, no, you dont need to use linux to learn networking principles. It may help, but it is by no means a requirement.
It's not necessary, but a lot of the documentation is written assuming you either have Unix knowledge or have access to a Unix box. I think Linux also gives you more control over network configuration than Windows, or at least makes it easier to access things (e.g., the hosts file). So while you don't need Linux, it's probably worth looking into.
When you say "network" I presume you mean to say "TCP/IP networking", as this is the prevailing technology used nowadays in LANs.
What you need to understand is that linux has TCP/IP implemented in the kernel itself, whereas MS Windows (and other OS) initially used different networking stacks and only added TCP/IP support later on. Microsoft initially used NetBIOS and NetBEUI, and also had strong sort for IPX/SPX, but these protocols are by now deprecated.
In consequence, TCP/IP networking in MS Windows used to be awkward when compared with the same in linux. However, these obstacles have by now by and large been overcome.
The fundamental principles are completely independent from any operating system, and there is no need to learn linux in order to become good with networking. Having said this (and I am a full time linux user), linux has many advantages to offer for web developers, and still has the edge when it comes to debugging networking issues or configuring special networking solutions, so it would in the long term definitely be to your advantage to be familiar with it.
On most linuxes configuring the network nowadays is just as easy as on windows so you won't learn much. Though knowing linux might be a good skill for a web developer.
More important is to understand the underlying network concepts and how it works. So you do not just know what to enter in which box in which dialog but you know why that value goes there. What the purpose of that value is. Because when you really know how and why you will be able to resolve problems much faster.