I trying to run a code where a server can check the flags in the packets it receives from client. I need to do that as a detection for TCP reset attack. So basically i want the server to be able to check if he is receiving multiple RESET packets.
any help please? i need that in python.
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I'm trying to write a TCP transparent proxy to run on Linux.
I want to, upon receipt of an incoming connection, initiate a corresponding outgoing connection, but only accept (SYN|ACK) the incoming connection if the outgoing connection is successful.
TCP_DEFERRED_ACCEPT doesn't do what I want -- it always sends a SYN|ACK.
The question is: how do I accept TCP connections, but defer the SYN|ACK, with the Linux sockets API?
You can do that with Linux, but not via the socket API. You would use the NFQUEUE target which allows you to redirect some packets to userspace and decide their fate from within your program.
Obiously, you'd still have to parse the packet in userspace, but searching for a few TCP flags should not be that hard and not require a complete TCP stack. And this way Linux still does the whole network job.
In your case, it would seem possible that you both use NFQUEUE and classical sockets API. The first will give you early decisions, the latter TCP stream data access. Although I never tried it.
See https://home.regit.org/netfilter-en/using-nfqueue-and-libnetfilter_queue/ for instance.
I'm an Automation Developer and lately I've taken it upon myself to control an IP Phone on my desk (Cisco 7940).
I have a third party application that can control the IP phone with SCCP (Skinny) packets. Through Wireshark, I see that the application will send 4 unique SCCP packets and then receives a TCP ACK message.
SCCP is not very well known, but it looks like this:
Ethernet( IP( TCP( SCCP( ))))
Using a Python packet builder: Scapy, I've been able to send the same 4 packets to the IP Phone, however I never get the ACK. In my packets, I have correctly set the sequence, port and acknowledge values in the TCP header. The ID field in the IP header is also correct.
The only thing I can imagine wrong is that it takes Python a little more than a full second to send the four packets. Whereas the application takes significantly less time. I've tried raising the priority for the Python shell with no luck.
Does anyone have an idea why I may not be receiving the ACK back?
This website may be helpful in debugging why on your machine you aren't seeing the traffic you expect, and taking steps to modify your environment to produce the desired output.
Normally, the Linux kernel takes care of setting up and sending and
receiving network traffic. It automatically sets appropriate header
values and even knows how to complete a TCP 3 way handshake. Uising
the kernel services in this way is using a "cooked" socket.
Scapy does not use these kernel services. It creates a "raw" socket. The
entire TCP/IP stack of the OS is circumvented. Because of this, Scapy
give us compete control over the traffic. Traffic to and from Scapy
will not be filtered by iptables. Also, we will have to take care of
the TCP 3 way handshake ourselves.
http://www.packetlevel.ch/html/scapy/scapy3way.html
I am trying to verify a new functionality added to the router kernel. So lets assume I added a filter,iptable and such. I have live traffic. I tried to use tcp dump and look into the packet header and see if the new values in the header are there but I am getting random traffic passing through.
I wonder if it is possible to have tcpdump send traffic and dump it so I have specific packets I sent ? or any other linux commands I can use to do the process. I have a destination port that has no traffic but I don't know how I can send to it and capture those packets. I did some reading on sendip and tcpdump and couldnt help myself.
Send packets, tcpdump it or something like that, verify the packet header has what I want and move on with my life.
I hope I was clear enough.
I am searching for a TCP traffic generator. The problem is that I do not simply want to send TCP traffic as it can be done with e.g. Iperf. I want to be able to configure the flags and other header fields and I want to react on incoming packets e.g. a TCP SYN.
So for example I want to send a TCP FIN packet if a TCP SYN arrives.
I prefer Linux tools but it would be also ok if the tool only runs under other OS.
I have looked into hping3, it looks promising. But I would like to look into other tools before choosing it.
SendIP can generate TCP packets, with options to manipulate SYN/FIN bits as well as other fields.
This sort of question really belongs on Server Fault.
After sending some tcp data by any method (mine is below)
DataOutputStream outToServer = new DataOutputStream(clientSocket.getOutputStream());
outToServer.writeBytes(string);
How can I verify in JAVA that TCP data is sent successfully? OR is there any way of reading the ACK received (from tcpserver) ?
You cannot. Operating systems typically does not expose this to applications.
If you need to know whether data has made it to the other end, you need to implement acks at your application protocol, not at the transport level that TCP concerns itself with.
I always use Wireshark to debug TCP apps. It is a TCP tracing tool that shows you the individual packets with their acks, retransmits etc.
It is not in code, but it does allow you to double check the behavior of your app.
Check wireshark.