I have a cable modem that has a 6 static IPs. One is the gateway, and the other 5 can be used for whatever I want.

The cable modem has 4 jacks on the back, and I plug 3 routers into those jacks. 2 of the routers are wired routers. They have the gateway addresses:

  • Router A:

  • Router B:

The server that is supposed to connect to the Internet is plugged into a LAN port on router B. My computer is plugged into the LAN port on router A. It is sort of looks like this:

enter image description here

From the server, the command,

nmap 74.XXX.XXX.XXX -p1-255


Host is up (0.00072s latency).
Not shown: 253 filtered ports
22/tcp open ssh
80/tcp open http

which is good. But on my computer the command:

nmap 74.XXX.XXX.XXX -p1-255 


Note: Host seems down. If it is really up, but blocking our ping probes, try -Pn
Nmap done: 1 IP address (0 hosts up) scanned in 3.21 seconds

From my computer, the command,

nmap 74.XXX.XXX.XXX -Pn


Host is up.
All 1000 scanned ports on 74.XXX.XXX.XXX are filtered

What do I need to do to have ports 80 and 22 open from the Internet?

  • What do you mean by "ISP router"? Are you saying that there is another router that is not listed? The ISP is Comcast. – VectorVortec Jun 10 '18 at 0:18
  • It is a D-Link Unified Services Router DSR-150. I made an attempt to forward the correct ports, and the ports seem to be open when tested from the server. Please see the command in the question. – VectorVortec Jun 10 '18 at 3:11
  • That is a lot of questions. I'll update my question to contain that information. In the meantime, the Comcast "cable modem" is a Technicolor Model # DPC 3941B. I haven't messed with it much, since it is Comcast's equipment. I probably can't get the requested information until Monday. On router B, I attempted to forward the ports, and they seem to be forwarded. I'll provide more details on Monday. Thanks for your help. – VectorVortec Jun 10 '18 at 4:18
  • The question is far too vague. Very little is exposed about the network configuration and that's far from enough. One thing seems to be clear though: The server is behind a NAT. No external traffic can get to it without port forwarding on both the routers and the cable modem. – user477799 Jun 10 '18 at 4:23
  • I think 74.XXX.XXX.XXX is the NATTED address of your server , the cable modem is doing the natting , so wehn the computer attempts to access the NATTD address it will send it out to the routers - and most routers I've tried can't send it back , they can only send it out to the ISP - so I dont know that you can test it like this - I could easily be wrong – Ross Jun 10 '18 at 4:28

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