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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

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