Once I reboot, this problem goes away, and it works again 1 time. In case you want to write the pcap file yourself, you can use libpcap , which is the low-level library upon which tcpdump, Wireshark and other network analyzers are built. The virtual interfaces are created, made persistent, assigned to an user, and configured by root for example, by initscripts at boot time, using tunctl or equivalent The regular users can then attach and detach as many times as they wish from virtual interfaces that they own. The architecture is similar to the one described in https: What goes in one end comes out the other. Older Ethernet frames are easy since they have a length field but Ethernet II packets have a type field. When a tun interface receives a packet, it’s like a normal phisical ethernet interface receiving a packet.

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To do this, it’s necessary to bridge, on the gateways ie, the hosts that run simpletun or another tunneling software that uses tap interfacesthe local LAN interface and the virtual tap interface together. Can you describe how you were able to create a tun and retrieve data to java code.

The problem I have is that once I exit this program that created the tap device ctrl-c or killI cannot ever get it to run again successfully without rebooting.

I understand the patch does the right thing, as having a process attached to the tun fd is the equivalent of having the “link up” for a tun interface; however, for the purposes of the article, this is a bit of a loss because the simple test described there to show how the interface works cannot be done anymore.


Do I have to change any other kernel parameters to make this work? So, just as linjx doesn’t run tcpdump on an ethernet interface with the cable unplugged, one shouldn’t attempt to do its equivalent on a tun interface.

Natural Born Coder

Did you try to bridge? June 16, at Second problem I have with named pipe. I create a user-mode tunnel using tunctl, but get a strange error message at run time. It is not simple as that. Then, not sure why the bridge is not seeing the frame.

The invalid flag argument was a mistake I had different version of this flag in the compiler and in the kernel But still not working on the router: You can help Wikipedia by expanding it. What I wanted to know from you is: The “real” data pinux, that exchanged by the high level applications – ping or ssh in the above example is never exposed directly on the wire although it IS sent in cleartext, see below. I read similar error up in comments but in a different situation By clicking “Post Your Answer”, you acknowledge that you have read our updated terms of serviceprivacy policy and cookie policyand that your continued use of the website is subject to these policies.

April 19, at It created a tun interface and logging the incoming packages but when I tried on my router OpenWRT – Backfire-rc4 nothing happend. I am doing exactly this: In the case of an error i think i should be able to detect it by comparing the IP-Packet-Size with the used space in receive buffer return value of read.

My tun is configured like so:.

Understanding TUN TAP Interfaces – Natural Born Coder

If I change the src IP of the intercepted packet,recalculate the required checksum and re-inject that packet, the packet gets forwarded to the proper interface. Then, I simply leave the tap devices linuux always and I they persist after my program exits.


The solution can be change the ioctls in the driver so that there be one for adding and one for deletion. I know the difference between the packet structure of the two IP vs Ethernet though I am not sure whether I can make the tun work as tap, by which the server which is configured only tintap read from a tap device will be able to read successfully.

What goes in one end comes out the other.

TUN/TAP – Wikipedia

What I am trying to do is configure the tun device to accept any packets headed to If it looks like it has to be delivered locally but there’s no process to deliver it to, then it’s dropped depending on the actual type of packet, an error may be generated. Check that the node liux the service has a route back liunx the tun node. I can’t read the the package out and it looks dropped somewhere. Is it possible tuntpa Another nice multipurpose network tool: So on the NS3 machine, you need two bridges, each bridge will include a tap interface which in turn goes into NS-3 as well as a physical interface, so roughly you’d have this interface names are just an example:.

What does it mean “I adjusted the Tap Read to read 32bit integers”?