Scapy p.07 – Monitoring ARP

Using Scapy in a Python Script

So far we’ve been working with Scapy in interactive mode. It’s very powerful but there are times when it would be easier to work with a Python script instead. In order to use Scapy, we have to import the Scapy module like this:

This will import all Scapy functions, but if you know that you will only need a few of the functions, you can import them individually as well like this:

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Scapy p.08 – Making a Christmas Tree Packet

We’ve doing a lot of packet sniffing, analysis, and even some basic packet crafting of our own. With the ICMP packets we created, we only set the destination we wanted to use and let Scapy take care of the rest.

Taking Control of Protocol Fields

I want to show you how to take a bit more control over the packet creation process by creating a TCP Christmas Tree packet. I’ll let you read the details, just know that the name of this packet comes from every TCP header flag bit turned on (set to 1), so it can be said the packet is “lit up like a Christmas Tree.” Continue reading

Scapy p.09 – Scapy and DNS

We’ve been able to work with Ethernet, ARP, IP, ICMP, and TCP pretty easily so far thanks to Scapy’s built in protocol support. Next on our list of protocols to work with are UDP and DNS.

DNS Request and Response

Using the sr1() function, we can craft a DNS request and capture the returned DNS response. Since DNS runs over IP and UDP, we will need to use those in our packet: Continue reading

Scapy p.11 – Scapy Resources

I hope you had as much fun as I did getting started with Scapy. These are all starter ideas, but we’ve barely uncovered the tip of the iceberg. I’ll continue to write articles about cool Scapy tools I come up with but you should dig into the docs below and see what you find. If you have any questions or comments about this guide, feel free to contact me.

Online Resources

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Scapy Sniffing with Custom Actions, Part 2

In the previous article I demonstrated how to add a custom function to change the formatting of the packet output in the console or do some sort of custom action with each packet. The limitation of just including a function name in the prn argument is that you cannot pass along any arguments other than the packet itself (implicitly passed).

Using nested functions to harness the power of closure, you can bind any number of arguments to the function that is executed on each packet by Scapy. From the part 1 article, you can see how we created a function and used the function to pass the actual function (not the returned value) to the prn argument:

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Scapy Sniffing with Custom Actions, Part 1

Scapy has a sniff function that is great for getting packets off the wire, but I recently discovered just how great this feature really is. There’s an argument to pass a function that executes with each packet sniffed. The intended purpose of this function is to control how the packet prints out in the console, allowing you to replace the default .nsummary display with a format of your choice.

In the ScapyDoc.pdf, the prn argument is defined as:

prn: function to apply to each packet. If something is returned, it is displayed. For instance you can use prn = lambda x: x.summary().

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First Pull Request

I submitted my first GitHub Pull Request today so I figured that this development thing is doable and I might as well write some articles about my coding exploration!

What I’m feeling right now is an overwhelming of all the fantastic resources out there, it’s just impossible to absorb info as quick as I find it. I’m finding that the people in the developer community are just as nice as those I’ve reached out to in the networking world. We really just want to get some bits from point A to point B, right?!?

Dev Tools I Use

This post quickly covers the tools I’m using after about 2 months of development study and practice. I will revisit this in a year or so to se what has changed and explain what tools I still use, and what tools end up getting replaced. My workflow seems to be very generic right now and it will be interesting to see how it changes as I mature as a developer.

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