I have a GSM modem that sends data via UDP (it appears) I have configured it to send all data to my public IP address over the internet but no data is arriving at my end so I need to troubleshoot.  I have confirmed that a TCP connection can be made from anywhere on the internet on the same port that the modem is supposed to be communcating on. Im using "Aggsoftware TCP/IP or UDP data logger" to listen for incoming data.  Is there software that I can use to test sending of UDP data?
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I'm got a video streaming application that runs fine in my office but fails miserably at the customer location. The symptom is that every couple of seconds, I stop receiving UDP packets for 2 seconds, then the stream resumes as if nothing is wrong.  I ran  at the customer location and it came back excellent. No dropped packets and low latency. The only difference I noticed between our two locations is that ping google.ca times-out at their location but works in mine.  How do I test whether the network I am on blocks incoming UDP packets? Is there a way for me to isolate who is dropping the packets?
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How to check the opened/closed ports on my computer?  I used netstat -a on command line.   Does the port status "LISTENING" indicate that the port is open? Is any port, that is not shown in the output, closed?
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I've never had to do IPC on Windows before. Currently I'm developing a pair of programs, a standard GUI/CLI app and a windows service. The app has to tell the service what to do. So, assuming the communication is local only, what would be the best communication method for these two processes?  Where best is defined as more robust and less error prone, not the most performant nor the easiest to code.  Code examples will be very welcome, but aren't required :-)  Note I'm asking about what to use, a standard TCP socket, named pipes, or some other means of communication only.  Thanks!
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Fist let's block all Incoming, Outgoing signals  via iptables.     vi /etc/sysconfig/iptables   *filter :INPUT ACCEPT [0:0] :FORWARD ACCEPT [0:0] :OUTPUT ACCEPT [0:0] -A OUTPUT -j DROP -A INPUT -j DROP -A FORWARD -j DROP COMMIT   start iptables:   service iptables start   My Ethernet Cable is plugged in. let's try something via terminal  ping 8.8.8.8 PING 8.8.8.8 (8.8.8.8) 56(84) bytes of data.   that is all. just 1 line. after that it stalls. clearly iptables is blocking it successfully  now I am going to disconnect my Ethernet cable. my internet is disconnected.  let's try it again:  ping 8.8.8.8 connect: Network is unreachable   this time .. instantly.. it returns that message.  Clearly, weather it is "ping" or any other program.. it is determining if a network interface is up or not before it executes it's internet command.  of course soon as it executes.. it is not able to pass through iptable rules. but what seems evident is.. it does not first consult to the iptables..  it first checks to see if a network interface is connected or not.   I would like to figure out how I can manually let it know that network interface is connected.  in other words unless I tell it network interface is up.. it should simply behave the same way it behaves when network interface is not connected ( when the ethernet cable is not plugged in)  how can this be done ?
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Is there a way to set a global DNS server that will be used for all connections (both Wi-Fi + cellular data)? If there isn't a uniform manner to specify DNS, can I just change the DNS used by the cellular connection?  Ideally, I am looking for an answer for vanilla iOS; however, I'd welcome any solution, including one that requires a jailbreak.
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Is OpenVPN UDP vulnerable to heartbleed?   I need to decide if I'm going to rebuild some servers, but they are very carefully firewalled; 1194/TCP is one of the firewalled ports (yay whitelist!).   1194/UDP is used (mission critical).
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I'm currently developing an internet of things device that utilizes a uBlox SARA-U260 gsm/3G modem.  In field testing, we have had significant software/firmware issues due to poor cell phone reception in our deployments in sub-saharan Africa.  I'm having a hard time duplicating the problems in the lab because the cell reception here is too good.  Even if there is no antenna plugged into the modem, it is still able to connect to the cell network internet!  So, I'm looking for the best way to thwart my modem into thinking it has bad reception.  One thought I had was to cut the coax cable of the antenna and solder a resistor between the gnd shroud and the center conductor.  Would this work?  What size resistor would make sense? Probably a fairly low-value resistor (say 50 ohm?)  I'm confused about why the modem can still connect even without an antenna.  I thought that during normal operation the modem must short the ground and center conductor when it is transmitting (hence the high current associated with a transmission burst).   Under normal circumstances, is the short locate inside the antenna?  If so, wouldn't the center conductor of the coax always be at ground potential (i.e. during reception)?  EDIT:  Thanks for the replies.  I have a big metal box sitting on my desk ready to mount the DUT (thanks for that acronym @Ali Chen ) tomorrow!
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I'm looking for a good link to data from Microcontroller to computer. I do not know what kind of communications is suitable for me.  I need a link which has a bit rate more than 50 Mbit/sec. and also it should be good enough reliable.  Moreover, I have not chosen the uC yet. What about these choices?   1-(uC side) USB to USB (PC side)  2-(uC side) SPI to USB (PC side)  3-(uC side) ethernet to ethernet (PC side)  Data is in fact received from a 16 channel ADC with a rate of 100 K. Data is processed in the uC and then would be sent continuously to PC.
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I'm now going on vacation, and I won't be having Internet connection there. I was thinking it would be a good time to browse through the Stack Overflow data dump. However, it's all in XML and I'd have to write a client to make it readable. Is there any existing client?
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Im trying to measure bandwidth, packet loss, latency and jitter between two computers on a wireless 802.11s mesh connection.   Im trying to make a (my first) bash script that can do the following:   SSH to another computer and start logging data from services (ptpd, tcpdump, iperf). Start the same processes on my own computer and start logging data. Once the iperf transmission on my own computer is finished, it should SSH into the remote computer and kill the the services.   The idea is for this these three steps run in a for-loop, that increases the package size transmitted by iperf for each iteration and logs the resulting data.  I know how to start a process on the remote pc by ssh host@adress process.  I am however clueless on how to start multiple processes through SSH and logout, since the processes are terminated once I logout. I have looked at the screen and nohup commands, but don't know how to use them in a script.  Thanks in advance!  EDIT:  Thanks for all the help so far.  I got nohup to work now, it was pretty simple as people pointed out.  So now I got: ssh host@adress nohup ./script.sh &gt; /dev/null 2&gt;&amp;1 &amp; in the script on my main pc. This starts a script on the remote pc just fine, and then logout of SSH. The next problem is how to execute the script on the remote pc as sudo, since this is needed by tcpdump.  Trying ssh host@adress **sudo** nohup ./script.sh &gt; /dev/null 2&gt;&amp;1 &amp; doesnt work.  Any ideas?  EDIT 2:  If anybody is stuck with the same problem, I found a guide how to solve this:
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I have a firewall with these simple rules:  iptables -A INPUT -p tcp -s 127.0.0.1/32 --dport 6000 -j ACCEPT iptables -A INPUT -p tcp -s 192.168.16.20/32 --dport 6000 -j ACCEPT iptables -A INPUT -p tcp --dport 6000 -j REJECT   Now, suppose I am using TCPDUMP like this:  tcpdump port 6000   And I have host 192.168.16.21 trying to connect to port 6000.  Will/should tcpdump output some packets coming from 192.168.16.21?
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Right now I'm in the process of possibly switching from a Cable provider to a DSL provider.  I  have both connections live, and before I cancel one or the other, I'm wanting to do some exhaustive testing of the internet connection.  I have three major questions:   What are some approaches that I can quantitatively test the speeds (both up and down) and quality of my internet connections (ping, time connection is down, etc,.)?   Are there other consideration that should be taken when testing an internet connection?   Are there any tools that can do this automatically and capture results?   Note: if you decide to suggest a piece of software, please  in doing so.  Also I'm looking to be able to save any data from the software for detailed analysis and comparison  Overall, I'm looking to compare the two connections over multiple periods of time such as peak hours (1600 - 2100 in my area), and with different loads such as streaming movies, uploading files, etc,.         This question was Featured in the blog!    Read the  for more details or  yourself
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I am configuring a Linux router with iptables. I want to write acceptance tests for the configuration that assert things like:   traffic from some guy on the internet is not forwarded, and TCP to port 80 on the webserver in the DMZ from hosts on the corporate LAN is forwarded.    alludes to a iptables -C option which allows one to ask something like, "given a packet from X, to Y, on port Z, would it be accepted or dropped?" Although the FAQ suggests it works like this, for iptables (but maybe not ipchains as it uses in the examples) the -C option seems to not simulate a test packet running through all the rules, but rather checks for the existence for an exactly matching rule. This has little value as a test. I want to assert that the rules have the desired effect, not just that they exist.  I've considered creating yet more test VMs and a virtual network, then probing with tools like nmap for effects. However, I'm avoiding this solution due to the complexity of creating all those additional virtual machines, which is really quite a heavy way to generate some test traffic. It would also be nice to have an automated testing methodology which can also work on a real server in production.  How else might I solve this problem? Is there some mechanism I might use to generate or simulate arbitrary traffic, then know if it was (or would be) dropped or accepted by iptables?
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I have written an app which will run on a server. I have little experience with network configuration and such things.  Now I have set-up the server and everything works how I want however I want 2 things   set the ip of my server to a static ip ideally be able to acces the server with a url like mytestserver.test or something like that   I do have experience with command line linux and windows but never needed to do anything with networks as I usually work with embedded systems  e\ my distribution is debian on the raspberry pi
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How can you find out which process is listening on a TCP or UDP port on Windows?
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I'm trying to diagnose and test some a Windows 7 domain-auth-over-wireless-network. I'd like to see what network the computer is connecting to, what auth it is using, and what DHCP data it receives prior to user login, and also what happens after user login. Does event viewer show this info? Do I need to enable it anywhere?  Cheers,  Victor
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The title pretty much sums it up.  I would like to send UDP traffic through a SSH tunnel.  Specifically, I need to be able to send UDP packets through the tunnel and have the server be able to send them back to me on the other side.  I know how to do it for TCP connections. Is this it possible with UDP?