Connecting two networks to one computer

May 31, 2011 at 18:50:13
Specs: Windows XP
Hi,

I am trying to connect the internet into an existing network with a server. There are four computers on this network, plus a server. The server address is 192.168.0.1. The request has been to only allow internet on two of the four computers. The four computers and the server are interconnected with a switch. The networked computers are all running Windows XP.

I have internet coming in through a modem, then into a router (IP 172.16.1.1), then from the router into the existing switch in which the existing network is connected through.

On the two computers requiring the internet have only one NIC. I have created two network connections by going to advanced and then adding an additional network. For the internet network, I have to following IP information set up on each computer:

Computer 1: IP 172.16.1.2
Subnet Mask: 255.255.0.0
Default Gateway: 172.16.1.1
DNS: 172.16.1.1

IP 192.168.0.102
Subnet Mask: 255.255.255.0

Computer 2: IP 172.16.1.3
Subnet Mask: 255.255.0.0
Default Gateway: 172.16.1.1
DNS: 172.16.1.1

IP: 192.168.0.3
Subnet Mask: 255.255.255.0

All computers on the network are required to share information with each other. The two listed above are required to be able to connect to the Internet and continue to be able to access information on all other computers on the network and the server.

The issue that I am having is that once I make the changes to the IP addresses, in order to add the internet network, I begin having various problems with the computers sharing information with each other. I am able to get computer 1 working OK (no issues with sharing or accessing the internet). However, computer 2 is able to access the server but not not able to access computer 1.

Any help you can provide in advising why this is not operating as expected would be greatly appreciated!


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#1
May 31, 2011 at 19:38:57
Have you already tried
ipconfig /flushdns
arp -d

at the computer in question?

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#2
May 31, 2011 at 20:33:23
RGM you have gotten some bad information sorry to say.

We only have one nic in each pc right?

If you truely have a modem and then a router, you should set the pcs to 'obtain ip address automatically'.
The router will give them a ip in the 192.x.x.x range with 192.x.x.1 for gateway and even dns.

By setting things as I describe all of your pcs will be in the same subnet [same street] so they can find each other.

The 172.x is what is on the wan side of the router. You can't use that for the lan side of the router.

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#3
May 31, 2011 at 20:44:58
@wanderer

172.16.1.1 is the LAN side of the router.

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Related Solutions

#4
June 1, 2011 at 00:16:09
I'm certain that the 172.16.1.1 is on the LAN side as I have set this as the IP address for the router which is connected to the modem.

@paulsep
I have not tried either of those commands. Can you advise why you are suggesting these (i.e. exactly what they do; I'm not familiar with these) and on what computers you would suggest that I run these commands?

Also, should all computers on the network have static IP addresses assigned. Before I tried to add the internet, only one computer on the network and the server had a static IP address. Everything else was set to obtain automatically.

Tks.


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#5
June 1, 2011 at 05:18:13
ipconfig /flushdns - is to clear the DNS-Cache entries made by windows. While you are working with the computer, windows will cache DNS-Entries here automatically.

arp -d - clears the ARP cache. ARP stands for Address Resolution Protocol. Try arp /? to get more informations.

These commands should be executed on computers, that do have problems connecting to the internet or to the local LAN.

Only the computer, that need internet access, needs static ip address, because the default gateway and DNS server entry must be 172.16.1.1.

Btw.: Which device acts as DHCP server in your LAN?

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#6
June 1, 2011 at 06:05:09
@paulsep

Just for clarification, there are two computers that require access to the internet, so would I set up both as noted in my initial note and noted below (I've included the entire network):

Computer 1: Needs to connect to internal network and Internet
(Internet Network Info - To connect to router which is connected to Internet)
IP 172.16.1.2
Subnet Mask: 255.255.0.0
Default Gateway: 172.16.1.1
DNS: 172.16.1.1

(Existing LAN Info)
IP 192.168.0.102
Subnet Mask: 255.255.255.0

Computer 2: Needs to connect to internal network and internet
(Internet Network Info - To connect to router which is connected to Internet)
IP 172.16.1.3
Subnet Mask: 255.255.0.0
Default Gateway: 172.16.1.1
DNS: 172.16.1.1

(Existing LAN Info)
IP: 192.168.0.3
Subnet Mask: 255.255.255.0

Computer 3: Needs to connect to internal network
(Leave as is??)
Obtain Automatically

Computer 4: Needs to connect to internal network
(Leave as is??)
Obtain Automatically

Server
IP: 192.168.0.1
Subnet Mask: 255.255.255.0
Default Gateway: 192.168.0.1
DNS: 192.168.0.1

Router
IP: 172.16.1.1

Great question about what is acting as the DHCP server. I have no idea. One would assume that it would be the server, but I haven't checked that. Why do you ask?

I was thinking about the situation more, and am ultimately perplexed as to why computer 1 was set up with a static IP address (before I touched the network) while all other terminals were set up to obtain automatically. Also, very confused as to why computer 1 when set up as noted above, can connect to the internet without issue and all other computers on the network, but I can only get the three other computers to see the server (and I think each other) but not computer 1. When I get rid of the Internet network (172.16.1.1) info from computer 1, everything works fine again. From what I've read, I should have the Internet network set up as the default gateway when creating two networks using one NIC.

Really appreciate your insight on this.


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#7
June 1, 2011 at 06:21:02
Ok, I got all of that.

Let's start with DHCP.
The router can't be the DHCP server, because in that case, all computers with dynamically assigned ip addresses would get 172.16.1.x ip address.

You can figure out the DHCP server by using ipconfig /all at one of the computers with dynamic assigned ip addresses.

For using only the local network in same subnet, you'll never need a default gateway, because all computers are in the same subnet and can see each other without asking the default gateway.
Default gateway is used only, if the domain name or ip address can not be resolved locally, which always happens, when you try to access the internet.
Because you local net is not aware of all the domains in the internet.

Therefore, the only computers, that need to have configured a default gateway, are the computers that need to access the internet. In that case, the default gateway is your router connected to the internet.

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#8
June 1, 2011 at 06:32:34
"There are four computers on this network, plus a server. The server address is 192.168.0.1. "

So why the heck is 172x even on this network???

I suspect RGM, the confusion here is the router came with the lan subnet 172x and you didn't realize you can configure it to the 192x network.

Unless there is another explaination of two subnets for 5 devices......

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#9
June 1, 2011 at 07:11:38
Every SOHO Router I've ever worked on came preconfigured using the Class C private IP range: 192.168.0.0

I've never seen one that used Class B.

Regardless, for all LAN computers to communicate with each other, they all need to be in the same subnet.............period, full stop.

Whether you're statically assinging TCP/IP settings or letting DHCP do it, this is the only way. If you put all in the same subnet and they have issues communicating with each other then something else is wrong. As long as all computers in the LAN can ping each other, the network is fine.


Your server is in a completely separate subnet from all the LAN computers. If you wish to have the LAN PC's and the server communicate, you need to give the server an IP in the same subnet as the rest. If you wish to have the server also have internet access, you give it the LAN IP of the router as it's Default Gateway and DNS settings.

Example using your IP addressing scheme:

DHCP Scope = 172.16.1.100 to 172.16.1.199

Server:
IP: 172.168.1.10
SM: 255.255.0.0
DG: 172.16.1.1
DNS: 172.16.1.1

All clients should get their IP's from DHCP unless they are providing a resource for the rest. If they are, then statically assign IP's not in the scope so as to avoid duplicate IP's. Statically assigned settings should include the same DG and DNS IP's as above.

Once done, all clients should communicate and have internet access. If for some reason you don't want a particular client PC to have internet access, but still maintain LAN access, you statically assign TCP/IP settings to it and leave DG/DNS blank.

It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.

***William Henley***


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#10
June 1, 2011 at 09:03:38
"Your server is in a completely separate subnet from all the LAN computers"

Missed this?

"IP 192.168.0.102
Subnet Mask: 255.255.255.0

IP: 192.168.0.3
Subnet Mask: 255.255.255.0

"All computers on the network are required to share information with each other."

We don't know if the "server" is running Active Directory. That's a big gotcha.

Otherwise the solution is simple:
set the router to 192.168.0.254
set the two computer for internet with that as gateway
set the other two to no gateway so they have no internet.
you would do this by statically assigning the ips to these workstations. no need for dhcp

RGM concerning your question of why one device was set to a static ip the answer is simple. That is standard for setting up a server.

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#11
June 1, 2011 at 09:12:32
Missed this?

Yep.........lol

I saw this:

Server
IP: 192.168.0.1
Subnet Mask: 255.255.255.0
Default Gateway: 192.168.0.1
DNS: 192.168.0.1

In his last response and went from there. Duh me!

Dual NIC's and dual subnets seems overkill for such a small setup. I still think a single subnet would cure all issues.

It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.

***William Henley***


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#12
June 1, 2011 at 10:29:42
Thanks so much for the awesome responses.

I think the main hangup I got into here is that I read some information stating that in order to hookup internet to the existing network, I would need to have two networks set up. Thus the reason why I was using 192.168 and 172.16. From everything said here, there was never ever a need for me to create two networks correct?

I also think I understand why computer 1 originally had a static IP address set up with default gateway of 255.255.255.0 and DNS of 192.168.0.1. Computer 1 has an email client that uses dial up to send and receive emails and also stores all messages which are accessible by the other PC's on the network. Thus "providing a resource for the rest" as noted by Curt R. Does this add up?

Also, want to mention that everything goes directly into a switch box. That includes all PC's, the server, and the router. With that in mind, having all devices within the same subnet will work correct?


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#13
June 1, 2011 at 10:48:21
And one other comment, Wanderer stated that "we don't know if the server is running active directory". Networking is not my forte if you haven't guessed already, but not sure exactly what this would mean to the setup at hand. Not sure if this is something to do with the operation of DHCP. I can only assume that the current setup for the server is that it is including DHCP serving as part of it's activities.

Actually, two comments. Here's the second. Computer 1 and 2 are the only computers that should have internet. Computer 1 shares a resource with the other clients so therefore needs to have a static IP, SNM, DG, DNS. Computer 2 can utilize DHCP. Computer 3 & 4 will not require internet and therefore should be set up with IP and SNM (no DG or DNS). Server does not require internet access, so set up static IP and SNM (no DG or DNS). Everything to be on the subnet 192.168.0.X. Make sense? In this scenario, what should be the DHCP server? The router or the server?


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#14
June 1, 2011 at 11:19:31
Neither. You don't need dhcp at all for this small amount of workstations/server.

To check if domain or workgroup logon to a workstation and go to Computer and right mouse click. Go to properties. Click on the computer name tab. Click on Change button. Is it in a domain or a workgroup? Click cancel when done.

Yes you only need one subnet not two.

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#15
June 1, 2011 at 15:30:26
@wanderer

I'm not on site for the next 6 days so not able to see whether it's a domain or workgroup. Can you please advise on what this has to do with what's been discussed thus far?

Tks


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#16
June 1, 2011 at 17:55:55
if a domain server there are local dns configuration issues which don't apply if not running Active Directory.

If running AD the forwarders need to be configured properly
The AD dns server would need the static host/ptr records for the local workstations
Workstations point to the MS dns server not dns on the internet.

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#17
June 2, 2011 at 06:07:38
I can only assume that the server is currently using DHCP since three of the four clients were originally set to obtain IP automatically. If I set everything up with static addresses, I'm assuming that I would have to deactivate DHCP on the server. Could someone please confirm that this is indeed necessary and if so, how this is performed on the server?

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#18
June 2, 2011 at 07:59:52
You would first determine what is providing the dhcp ips by going to a workstation and doing a ipconfig /all and noting what ip address is listed for dhcp server.

depending on if server or router will determine which you disable.

on server you can just disable the dhcp server service.

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#19
June 7, 2011 at 06:47:12
@Wanderer

Just curious, is it necessary to disable DHCP services on the server? Would the network still function correctly if all clients had static IP's set with DHCP running on the server?


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#20
June 7, 2011 at 07:52:41
That will work until someone adds a pc using dhcp then you can possibly get ip conflicts.

rule of thumb: disable services you are not using.

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