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nashsclay's avatar
nashsclay
New Contributor

DPC3825 router/modem combo unable to port forward fully

I have the DPC3825 router/modem combo. I use it for both hard wired and wireless connections. I want to SSH, remote in, on port 22 to a small linux machine I have. I have a another linux machine that when I plug it into the combo unit it automatically opens up port 22 and I can access it from outside my LAN network.  The port is not opened on the combo unit either. So I plugged in my other linux unit, set it up properly (from what I know) and can't SSH into it. I then opened the port up and still can't SSH into the new linux unit. It does not make sense to me how my first linux box can be accessed outside the network with no ports forwarded on my combo unit. Any advice on what I can do?

Further, can I go to my local cox store and switch out my combo unit I received from them and get just a modem with no wifi? Thanks! 

connection issues
DPC3825
ssh

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  • Tecknowhelp's avatar
    Tecknowhelp
    Valued Contributor II

    So as I understand, you have two machines, and you can SSH into one, but not the other(B)? How do you have your port forwarding rules set up? Can you SSH into unit B from unit A?

    And yes, you can switch. If you don't rent the gateway, you can buy a stand alone modem from anywhere and add it to Cox as long as it's on this list. 

  • nashsclay's avatar
    nashsclay
    New Contributor

    Thank you for the reply. I can SSH into both devices when they are both connected to the router/modem combo. That's the thing with the port forwarding rules, when I tried it with (let's keep things simple and say unit A is the unit that can be SSH into from outside the LAN) unit A, it didn't matter what the ports were that were forwarded. I added the port 22 and could access unit A from the outside. Then removed the port, could still remote in to unit A. Unit B could only be SSH into from inside the LAN with any machine.

  • Tecknowhelp's avatar
    Tecknowhelp
    Valued Contributor II

    There two network directions; inbound and outbound. When you port forward port 22 to unit a, it creates a routing path from unit C(computer outside LAN) to router then to unit A. When you disconnect unit A, that routing path still exsist, even if you change the port forwarding rule. It would need to time out, or you would need to reboot(soft) to clear the table to allow a new connection to unit C.

    Instead of having to swap the rules and reboot each time, use a different port for each unit. First add IP reservations for unit a to be 192.168.1.a and unit b 192.168.1.b and then forward 22 to 192.168.1.a and port 2222 to 192.168.1.b. Not only would this be easier, but you could access both at the same time.

  • nashsclay's avatar
    nashsclay
    New Contributor

    UPDATE: So I fixed it with buying new hardware. I returned my combo router/modem and got just a regular modem from cox. Then I went to a retail store and bought a Netgear AC1750 (not saying you have to get this one) router and hooked it all up. The ports forwarded instantly! If you need to port forward, don't get a combo unit, especially one given to you by cox. And to further that, I could hardly access the admin panel on the old combo. Get something good, you won't regret it. I also added port 2222 for the second machine but that port is too slow for SSH. But I can SSH in to both machines outside of my Lan. Just now to figure out if it's possible to specify what machine I want to ssh to while using the same port 22...... and thanks Tecknowhelp for the help!