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Are there any tools that would allow me to "manually" step through the network-stack processes of a device connecting to a network and communicating with other devices? Similar to using PuTTY to manually mimic a web browser through sending and receiving manual GET/POST requests, headers, user-agents, cookies, etc.

I'm trying to find a "simulator" tool for understanding the network stack/OSI model. I understand them generally, but am looking for a hands-on tool that allows one to step through the processes of what a network device does automatically behind-the-scenes when coming online to a new network (sending broadcast packets, responding to ARP, etc).

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    HTTP is only a single layer, and there are a lot of tools that can do this. To learn the whole OSI stack though, you'll need a tool that can mimic not just HTTP requests, but also simulate the TCP layer, IP layer, then the data and physical layer. The former two are usually implemented by the operating system; the latter two are usually not even accessible by the operating system, so any such tool would have to emulate hardware. – Lie Ryan May 18 '15 at 0:26
  • What are your actual question you're looking for? Are you only interested in one layer or are you looking for an all-in-one tool stack that lets you step through all layers? The former query is easier, the latter, I have never seen one. – Lie Ryan May 18 '15 at 0:28
  • @LieRyan To clarify, I was just using Putty + HTTP layer as an example. I'm more interested in doing this around the network layer, like with networking/routing/ARP/etc. Ideally, an all-in-one tool would be great. But if none exists, then a tool based around the network layer would be preferable. – Coldblackice May 18 '15 at 2:40
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    I recommend to capture traffic and look at it using wireshark, since you can look with it very detailed at the various layers. Once you've understand what's going on you might use tools like scapy to construct your own traffic. – Steffen Ullrich May 18 '15 at 4:40
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    I remember using such a tool during my studies at school, alas it was in-house build and we were not allowed to take it with us. if anyone knows an open variant that would be a big help here. – LvB May 18 '15 at 10:09
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The problem with what your asking for is that there isn't a 1 to 1 mapping of the OSI layer to actual implementations. The OSI layers are really conceptual more than physical. In reality, the demarcation between the various layers is very blurred, which makes it near impossible to implement a tool which can break things up and break them into specifric layer operations. I have seen some simulators used for teaching purposes, but don't know of any which are free or open source. Being simulators, there is only a limited amount of value in them anyway.

My recommendation would be to use wireshark to monitor traffic and then perform some standard activities, such as an http and https session, a telnet/ftp session, sending a email message, ping, traceroute etc. You can capture the traffic and then use wireshark to inspect what is going on. As a tool, it is very powerful, but like most powerful tools, it can take a while to learn. However, the interface and filtering options are pretty good and it provides a good way to 'zero in' on various levels of the network traffic.

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