Skip to main content

tcp - How to prove provider is blocking incoming traffic on some ports?

I hope this is not too much focused on home networks, because that's where I hit the problem, but I think it may be of general interest nonetheless.


I have a cable connection (Cisco EPC3208) and a NAS (Synology DS413). Basically, I have problems setting up the samba share for access from the internet, but I found out the problem is much more general. So suppose I want to set up an SSH server on the NAS and I can chose the port freely. If I connect the NAS to a router, I can use any port and the SSH server will be seen under that port within my local network. Now, having connected the NAS to the cable modem, I am not able to connect to the SSH server if it is running on one of the ports 135, 137, 139, 445, 3127 and 9898. All other ports that I tested, including 134, 136, 138, 140, 444, 446, 3126, 3128, 9897 and 9899, these all work. I could confirm this from three remote locations, work, university and 3G, as well as using an external port scanner [1]. The NAS firewall is off. So I am pretty sure incoming traffic on these ports is blocked by my provider, "for security" probably.


My cable provider (Unitymedia, Germany) claims to not block any traffic, repeatedly. They ask me to contact the router manufacturer (I told them I do not use one), asked me to double-check my NAS configuration (I told them I can connect just fine internally when using a router), and so on and so on - not of interest here.


Now, what can I do to prove that they ARE blocking traffic on these ports (provided they are), either in their network or in the cable modem? Is there any way to trace a packet sent to a specific port and see where it's lost, similar to a traceroute?


[1] http://www.heise.de/security/dienste/portscan/test/go.shtml?scanart=1

Comments

Post a Comment

Popular Posts

How do I transmit a single hexadecimal value serial data in PuTTY using an Alt code?

I am trying to sent a specific hexadecimal value across a serial COM port using PuTTY. Specifically, I want to send the hex codes 9C, B6, FC, and 8B. I have looked up the Alt codes for these and they are 156, 182, 252, and 139 respectively. However, whenever I input the Alt codes, a preceding hex value of C2 is sent before 9C, B6, and 8B so the values that are sent are C2 9C, C2 B6, and C2 8B. The value for FC is changed to C3 FC. Why are these values being placed before the hex value and why is FC being changed altogether? To me, it seems like there is a problem internally converting the Alt code to hex. Is there a way to directly input hex values without using Alt codes in PuTTY? Answer What you're seeing is just ordinary text character set conversion. As far as PuTTY is concerned, you are typing (and reading) text , not raw binary data, therefore it has to convert the text to bytes in whatever configured character set before sending it over the wire. In other words, when y...
Post a Comment
Read more

linux - Extract/save a mail attachment using bash

Using normal bash tools (ie, built-ins or commonly-available command-line tools), is it possible, and how to extract/save attachments on emails? For example, say I have a nightly report which arrives via email but is a zip archive of several log files. I want to save all those zips into a backup directory. How would I accomplish that? Answer If you're aiming for portability, beware that there are several different versions of mail(1) and mailx(1) . There's a POSIX mailx command, but with very few requirements. And none of the implementations I have seem to parse attachments anyway. You might have the mpack package . Its munpack command saves all parts of a MIME message into separate files, then all you have to do is save the interesting parts and clean up the rest. There's also metamail . An equivalent of munpack is metamail -wy .
Post a Comment
Read more

performance - Single Threaded Qaud Core v.s Hyper-Threading Dual Core

Let's say we have two CPUs, One is Quad Core 3.2 Ghz with 4 Cores, and We have a Dual Core 3.2 Ghz with 2 Cores with 2 threads in each Core (Hyper-Threading). My assumption as a programmer will be, the 4 cores 4 threads should perform faster than 2 cores 4 threads since the second CPU needs to switch between threads in order to emulate 4 cores while the first one doesn't need to perform such switching as each core can perform independently and individually. I want to confirm that my assumption is true, if not please explain why one is better than the other. Answer I do believe thats true - since hyper threading does share some elements - specifically the main execution resources, you'll be able to run 4 full threads at once, rather than waiting for those resources to be freed up. The point of HT is to get better performance with a smaller use of die area - your quad core would generally be a bigger chip - say almost twice as large, than a non HT dual core chip, while a HT...
Post a Comment
Read more

freeze - How do I stop windows 8.1 from freezing when the screen locks

This happens to me on a regular basis if I leave the computer for upwards of 10 minutes. It didnt do so at first but started after a couple of days. This is possibly related to further windows updates although nothing seems to tie in obviously when looking at my update history. I have to hold the power button in to power off. If the screens have switched off aswell they wont come back on, if they haven't I see the login picture and can move the mouse pointer but nothing happens and no combination of keyboard mashes or mouse clicks lets me see the login prompt. In the event log (type event viewer into the start menu) under system before every Critical problem (me powering down the machine without restarting) I get distributedCOM errors talking about this guid: "The server {BF6C1E47-86EC-4194-9CE5-13C15DCB2001} did not register with DCOM within the required timeout." I also get the same error for this 1B1F472E-3221-4826-97DB-2C2324D389AE. This seems to be a common theme and...
Post a Comment
Read more