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[kumi_]

Hi folks,

I'm struggling to understand some basic networking concepts, I hope someone can help me out.

I have Time Warner Cable (TWC) Internet service. The TWC modem is connected to the DIR-655 uplink port. Computer A and Computer C are connected to the DIR-655 via GbE cable.

SCENARIO 1
DIR-655 <--GbE--> Computer A
            <--GbE--> Computer C

In this situation, Computer A and Computer C share the same public IP.

I'm adding a computer in the same room as Computer A. For various reasons, I can't connect it directly to the DIR-655. I'm considering buying a network switch (i.e. a DGS-2205), and setting things up like this:

SCENARIO 2
DIR-655 <--GbE--> Computer C
            <--GbE--> DGS-2205 <--GbE--> Computer A
                                         <--GbE--> Computer B

Will Computers A, B, and C all have different public IP addresses? If not, how will the two switched computers be be able to access the internet?

When I bypass the DIR-655 and connect a computer directly to my cable modem, I can setup bridged networking, and the second computer will acquire a unique public IP address. Like this:

CableModem <--GbE--> (nic1) Computer A (nic2) <--GbE--> Computer B
                                         123.45.67.01                       123.45.67.99

Multiple public IPs is pretty handy. I'm just wondering if this will still be the case in SCENARIO 2.

Thanks to anyone who can clarify

[Lycan]

The router acts as a medium between the public ip address and the local network.
Scenario 2 is the correct set up.

[kumi_]

I see, so everything downstream of the Router will share the same public IP address, even if it's behind a switch.

Is there any way to configure the DIR-655 to allow connected devices to pass-through DHCP requests to my cable modem, so they can all have different public IP addresses?

[davevt31]

Time Warner is only going to give you one address.

[kumi_]

I don't think so...

I have connected 2 virtual WinXP instances to the Internet (using bridged networking in vmWare.) The physical machine + the 2 virtual machines all get distinct public IPs, and they can simultaneously connect the internet.

[davevt31]

The Virtual machines are not getting their addresses from Time Warner, they are actually using the built-in DHCP services that is part of vmware.  This passes through the Host nic to connect out.

http://www.vmware.com/support/ws4/doc/network_bridged_ws.html

[kumi_]

Here's my ethernet adapter in the host machine:

        IP Address. . . . . . . . . . . . : 76.189.249.xxx
        Subnet Mask . . . . . . . . . . . : 255.255.224.0
        Default Gateway . . . . . . . . . : 76.189.192.1
        DHCP Server . . . . . . . . . . . : 76.58.128.1

I start my guest virtual machine, and it's ethernet adapter reads:

        IP Address. . . . . . . . . . . . : 76.189.219.yyy
        Subnet Mask . . . . . . . . . . . : 255.255.240.0
        Default Gateway . . . . . . . . . : 76.189.240.1
        DHCP Server . . . . . . . . . . . : 76.58.128.1


That's my ISP's DHCP server, and those two public IP addresses are assigned by my ISP. Only "Host-only" and "NAT" VMware adapters use built-in DHCP. I'm using "bridged".

I'd like to replicate this behavior in my physical network, somehow.

[kumi_]

Now I'm imagining something with 2 switches:

Code: [Select]

Cable Modem
  + DGS-2205
    + DIR-655
      + Computer X
      + Computer Y
    + DGS-2205
      + Computer A
      + Computer B
DIR-655, Computer X, and Computer Y will share the same public IP. Computer A and Computer B will have unique public IP addresses. Is that right?

[davevt31]

The Virtual machine should not be getting a real IP address from TW.  The vmware setup is just making it look like you are, that is the way that bridged networking works.

If they were both getting real IPs from TW the gateway should be the same.

[davevt31]

I might be confusing the vmware "Bridged" term, I haven't used vmware in about 5 years.  If you are paying Time Warner for more than 1 public IP address then the switch scenario should work, however I havn't seen them do that in a home environment usually it is just a typical cable modem with one IP assigned to it.

[kumi_]

1) The virtual public IP address is different from the physical public IP address.
2) It shows as unique when going to i.e. whatismyip.com
3) It's fully functional and non-shared. If I run 2 webservers on port 80 in the virtual and physical machines, browsing to each public IP from the internet will show different webservers.

I assure you it's a real IP.

EDIT: My cable service has always been like this, I'm not paying for any extra service beyond the standard residential plan. Maybe it's a left-over from my previous service provider Adelphia, which TWC took over recently.