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[jackb602]

I currently am using the DGL-4100 router at my office.  With the Dynamic DNS feature (and an account at DynDNS.org), I can access an FTP server on my office workstation from my laptop at home, or from any other location.  Everything works as expected.  The connection is: Internet > Modem > DGL-4100 > Workstation.

We are now considering reconfiguring the office network.  It may be necessary for my DGL-4100 router to be behind a switch.  So the proposed connection would be: Internet > Modem > Switch > DGL-4100 > Workstation.  Will the Dynamic DNS feature of the DGL-4100 still work if it's behind a switch?  If so, what are the settings I need to apply to the switch to make it work?

Thanks,
Jack

[ddwinell]

The Switch should not block any traffic including DynDNS registrations. Although being that you have your modem then switch leads me to believe that there are multiple devices getting IPs from the modem. What is the WAN IP of your DGL-4100? It sounds like you're double NATed, which would cause your DynDNS name to fail when trying to connect to your FTP.

[jackb602]

Thanks for the reply.  I'm more or less a beginner at networking so I'm not sure what you mean by "there are multiple devices getting IPs from the modem".  But maybe this will answer your question.  The proposed network would include a swtich immediately after the modem.  Connected to this switch would be my router and two additional switches.  (We are three businesses sharing a single space, and the other two businesses each get their own switch.)

Currently, my the DGL-4100 has a WAN IP address of 24.136.x.xxx (don't know if it's safe to post a complete IP adress.)  It is immediately behind the modem right now, and there is no switch involved.  So I assume that my router is assigning local IP addresses to the three computers connected to it.

And finally, what does "double NATed" mean?

Thanks,
Jack

[AWDL]

Double NAT'd means you have to devices performing NAT between your computer and the internet. Many Internet Routers including the DGL-4100 and some Modems perform NAT. One way to tell is if your DGL-4100 gets a private IP address on the WAN port. In your case, as it is now, you get a public IP (24.136.x.x).

Whomever is expanding the network for the three businesses should be able to help you understand the set-up you will get and also know if your needs will be met.

[jackb602]

Since Dynamic DNS works with my current configuration (Internet > Modem > DGL-4100 > Computer), and my router gets a public IP on the WAN port, I assume that I'm not being double NATed.  Is that correct?

Does a switch typically perform NAT?  I guess my basic question is: will the outside world (i.e. the DynDNS.org server) be able to see my router if it is behind a switch?  If so then we can go ahead with the changes.

The person expanding the network didn't seem to know the answer to these questions.  Hence my posts here. 

Thanks,
Jack

[AWDL]

Because your router gets a Public IP is why I say it is not going through NAT to get to your DGL-4100.

A Switch does not perform NAT.

Dynamic DNS should work going modem >switch > DGL-4100 > PC

The hesitation in the responses you get is because you mentioned 3 businesses will be connected to a switch connected to a modem. One wonder if the IP scheme is changing.

Do you get multiple public IP through the modem? If not, you will generally have to NAT to get multiple hosts (businesses) Internet connection.

Not knowing the configuration of your network and what the IP scheme is going to be, it is hard to answer the question. If the Tech working on this is from the ISP,  he/she may be putting the modem into NAT mode (instead of bridge mode) to get multiple connections before your DGL-4100.

[jackb602]

Ok, I think it's coming together for me now.  So the switch is "transparent" with respect to the DGL-4100; it doesn't interfere with the Dynamic DNS feature.  But if the switch is not performing NAT, does that mean that each of the other two businesses will need its own router as well?

So the configuration would be Internet > Modem > Switch > 3 Routers (each performing NAT).  Is that right? 

The networking tech is not from the ISP, so I don't think he plans to do anything to the modem.  Now that I understand this better, I'll e-mail him to find out what he plans to do.  Thanks for all your help!

Jack

[ddwinell]

Actually, in that case the modem would have to perform NAT to give the other locations behind the switch an IP address. Unless your ISP provides you with multiple public addresses.

A Switch is generally "transparent" or unmanaged (you don't configure anything). So the Modem would have to be the NAT device, taking the Public IP (your 24.xxx.xxx.xxx address) and translating that to a private range for each business IE 192.168.1.xxx. At this point if you used a router you would be Double NATed and this would break your DynDNS.

The way it would work with a switch is if you had Three Public IPs from your ISP, Modem (Bridge Mode, no NAT) > Switch > Router at each location with statically Assigned IP from ISP.

[jackb602]

I see.  The other scenario we were considering was Internet > Modem > Router > 3 switches.  If I understand you correctly, the router in this case would perform NAT for all machines behind the switches.  In this case, would the router still be able to point to my FTP server if it were behind one of the switches?  Maybe that would be the best solution. 

Thanks,
Jack

[ddwinell]

If it has a public IP address.

[jackb602]

If the router has a public IP address?  In this scenario, it would have a public IP, and the modem would not perform NAT.

[ddwinell]

yes that should work fine. Sorry read your post too quickly.

[jackb602]

Great, that makes sense.  Here's one more question that is probably very basic.  If the router is using the Dynamic DNS feature to point to my FTP server (which would be behind a switch), how does it know which port on the switch to point to?  Or does it just send that information to all the machines on that switch, and the one I've identified as an FTP server responds?

Again, thanks for all the help.  This is very informative.

Jack

[ddwinell]

The switch has an ARP table (address resolution protocol) which knows what IP is bound to what port on the switch by MAC ID.

[AWDL]

But to be clear. In the most basic version of the set-up you describe, you will not have a very private network from the other 2 businesses and each other.

At some point the other businesses may want services to pass -through the router to their servers. It would take a network consultant to review your and the other businesses situations/ needs / costs to implement the right solution.