Think of all application software within the computer as individuals in the house (you, your mother, your father, your sister, your brother, etc- you all are software applications, lol.) Think of your device as a house, let say your home. To simplify, one way is by inspecting the incoming request, and checking the destination " port" of the packet. However, how does this firewall know what request is "unsolicited"?This is based on what we call the firewall policy. On many networks, the software firewalls are mostly used, and they are pre-installed into your device system. There are two forms of firewall: the hardware and the software. Think of firewalls as those "gate-keepers" that secure your device against "unsolicited" access. So, we need some sort of GATE-KEEPER to guard our device, and either accept the request/response or decline it. Now, on a network(let's use a LAN- Local Area Network- for simplicity), where we have multiple devices, we would not want any external device, even the ones on our LAN to send us any unsolicited request without our consent, right? Mind you, my use of "us", "you" and "your" in this context represents your personal device on the network. The same thing goes for a client on a network (you only consume the services provided by the server.) What Identifies you as a server on a network is simply if your device/node(computer, printer, etc.) renders some sorts of services on that network- and/or beyond. In the previous post about TCP/IP protocol stacks, I mentioned that in the application protocol layer, we have several protocols that are implemented/used by the various applications on your device (whether you're a client or a server on a network!). First, what are firewalls and ports on a computer? Since this is a simplified version, I'd like to only provide you with descriptive information about them.
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