Different Private IP's on the Same Subnet

[Guest]

Here is my situation. I have one computer that controls a piece of equipment
and must also be able to access our corporate network. The house network is
using 172.X.X.X via DHCP (NIC1) and the equipment requires the private IP
10.X.X.X (NIC2). The equipment's IP cannot be changed. Both are using the
same subnet 255.255.255.0. The problem is that the equipment software wants
to access the house 172 IP when it needs the private 10 IP. Since, the
computer already has two NIC's installed, would installing a router for the
10.X.X.X segment solve the problem? Thanks for all of the assistance.

 

[Steve Winograd [MVP]]

Here is my situation. I have one computer that controls a piece of equipment
and must also be able to access our corporate network. The house network is
using 172.X.X.X via DHCP (NIC1) and the equipment requires the private IP
10.X.X.X (NIC2). The equipment's IP cannot be changed. Both are using the
same subnet 255.255.255.0. The problem is that the equipment software wants
to access the house 172 IP when it needs the private 10 IP. Since, the
computer already has two NIC's installed, would installing a router for the
10.X.X.X segment solve the problem? Thanks for all of the assistance.

I suspect that the problem is an incorrect subnet mask for NIC2.
First, I'd like to give some background information. Please forgive
me if I'm repeating things that you already know or if I've
misunderstood your setup:

1. 255.255.255.0 is a subnet mask, not a subnet. By itself, the
subnet mask doesn't tell you anything about what subnet a NIC is in.
The subnet mask can be different for each NIC.

2. A NIC's subnet is the range of IP addresses that the NIC can access
directly on its local area network. The subnet is determined by
combining the NIC's IP address and its subnet mask

3. Your two private IP addresses are in different subnets, and, if I
understand your setup correctly, that's how it should be. You want to
separate traffic intended for the house network from traffic intended
for the equipment network.

4. A router lets hosts on different subnets communicate with each
other. If I understand your setup correctly, you don't need a router.

Here's the subnet for each of your NICs, given that each has a subnet
mask of 255.255.255.0:

1. The NIC1 (house network) subnet is 256 addresses starting with
172.X.X. For example, if X.X is actually 16.0, the NIC1 subnet is
172.16.0.0 to 172.16.0.255.

2. The NIC2 (equipment network) subnet is 256 addresses starting with
10.X.X. For example, if X.X is 0.0, the NIC2 subnet is 10.0.0.0 to
10.0.0.255.

What IP address does the equipment software want to access when it
ends up using the house network instead? I suspect that the desired
address doesn't have the same X.X as NIC2. For example, if X.X is
0.0, then addresses that start with 10 but don't have zeros in the
next two positions (such as 10.1.0.1, 10.0.1.1, 10.2.3.1) aren't in
NIC2's subnet. and aren't accessible using the equipment network.

If you want all addresses that start with 10 to be in the equipment
network's subnet, change the subnet mask for NIC2 to 255.0.0.0.

If that doesn't help, please post a news group reply with full details
of your setup: the actual IP addresses of NIC1 and NIC2, the IP
address that the equipment address wants to access, a copy of the
computer's route table, etc. To write the route table to a text file,
open a command prompt window (Start > Run > cmd) and type this
command:

route print >route.txt
--
Best Wishes,
Steve Winograd, MS-MVP (Windows Networking)

Please post any reply as a follow-up message in the news group
for everyone to see. I'm sorry, but I don't answer questions
addressed directly to me in E-mail or news groups.

Microsoft Most Valuable Professional Program
http://mvp.support.microsoft.com

 

[Guest]

First, thanks for the extremely fast reply. Now the details...

NIC1 (Equipment) 10.1.1.100
NIC2(House Network via DHCP) 172.20.30.42

Both currently use subnet mask 255.255.255.0. I've changed the subnet mask
for NIC1 to 255.0.0.0. The equipment is trying access the 172.20.30.42
address instead of the 10.1.1.100. The two pieces of equipment are
10.1.1.101 and 102.

I've attached the route table. Thanks again.

Active Routes:
Network Destination Netmask Gateway Interface Metric
0.0.0.0 0.0.0.0 172.20.30.2 172.20.30.42 20
10.0.0.0 255.0.0.0 10.1.1.100 10.1.1.100 20
10.1.1.100 255.255.255.255 127.0.0.1 127.0.0.1 20
10.255.255.255 255.255.255.255 10.1.1.100 10.1.1.100 20
127.0.0.0 255.0.0.0 127.0.0.1 127.0.0.1 1
172.20.30.0 255.255.255.0 172.20.30.42 172.20.30.42 20
172.20.30.42 255.255.255.255 127.0.0.1 127.0.0.1 20
172.20.255.255 255.255.255.255 172.20.30.42 172.20.30.42 20
172.21.17.152 255.255.255.255 172.20.30.1 172.20.30.42 1
224.0.0.0 240.0.0.0 10.1.1.100 10.1.1.100 20
224.0.0.0 240.0.0.0 172.20.30.42 172.20.30.42 20
255.255.255.255 255.255.255.255 10.1.1.100 10.1.1.100 1
255.255.255.255 255.255.255.255 172.20.30.42 172.20.30.42 1
Default Gateway: 172.20.30.2

 

[Ron....]

Sounds like Reynolds?

 

[Guest]

NIC1 (Equipment) 10.1.1.100
NIC2(House Network via DHCP) 172.20.30.42

Your IP setup looks OK.

Just wondering, on what basis does the software on 1.100 decide what IP/card
to use? If it's trying to access a hostname rather than an IP, that may be
where your problem lies.

 

[Steve Winograd [MVP]]

First, thanks for the extremely fast reply. Now the details...

NIC1 (Equipment) 10.1.1.100
NIC2(House Network via DHCP) 172.20.30.42

Both currently use subnet mask 255.255.255.0. I've changed the subnet mask
for NIC1 to 255.0.0.0. The equipment is trying access the 172.20.30.42
address instead of the 10.1.1.100. The two pieces of equipment are
10.1.1.101 and 102.

I've attached the route table. Thanks again.

Active Routes:
Network Destination Netmask Gateway Interface Metric
0.0.0.0 0.0.0.0 172.20.30.2 172.20.30.42 20
10.0.0.0 255.0.0.0 10.1.1.100 10.1.1.100 20
10.1.1.100 255.255.255.255 127.0.0.1 127.0.0.1 20
10.255.255.255 255.255.255.255 10.1.1.100 10.1.1.100 20
127.0.0.0 255.0.0.0 127.0.0.1 127.0.0.1 1
172.20.30.0 255.255.255.0 172.20.30.42 172.20.30.42 20
172.20.30.42 255.255.255.255 127.0.0.1 127.0.0.1 20
172.20.255.255 255.255.255.255 172.20.30.42 172.20.30.42 20
172.21.17.152 255.255.255.255 172.20.30.1 172.20.30.42 1
224.0.0.0 240.0.0.0 10.1.1.100 10.1.1.100 20
224.0.0.0 240.0.0.0 172.20.30.42 172.20.30.42 20
255.255.255.255 255.255.255.255 10.1.1.100 10.1.1.100 1
255.255.255.255 255.255.255.255 172.20.30.42 172.20.30.42 1
Default Gateway: 172.20.30.2

Thanks for the additional information. I see one unusual thing in the
route table: the second line shows that NIC1 has its own IP address as
its default gateway.

The default gateway is the address of a router elsewhere on the
network that has a connection to other subnets (such as the Internet)
for use when an IP address isn't on the local network. Remove the
default gateway specification from NIC1.

I don't see anything else that could cause a problem in network
access. However, I don't understand what the problem is that you're
seeing. Please the problem in as much detail as possible, including:

1. What is the equipment software trying to access?

2. How is the equipment software trying to access it?

3. How do you know that it's using the wrong IP address or network?

4. What would be happening if everything worked right? How would you
know?

4. What happens if you disable the house network and try using the
equipment software?
--
Best Wishes,
Steve Winograd, MS-MVP (Windows Networking)

Please post any reply as a follow-up message in the news group
for everyone to see. I'm sorry, but I don't answer questions
addressed directly to me in E-mail or news groups.

Microsoft Most Valuable Professional Program
http://mvp.support.microsoft.com

 

[Guest]

I will try removing the gateway from NIC1 next week as I am out until then.
Also, to answer your questions...

1) When the software is launched, it looks for the two peripheral pieces of
equipment at 10.1.1101 and 102, then checks for the "server" which is the PC
at 10.1.1.100. I found that the subnet mask for the equipment LAN needs to
be 255.255.255.0.

3) You can monitor the software startup in a a status bar as it's loading.
When it gets to the PC IP it says it's trying to access the 172.20.30.42
house address which is incorrect.

4) If everything were operating correctly, the software would launch
successfully and bring up a ready window. As it currently stands, the
software locks up and crashes if it accesses the incorrect IP.

Thanks again for your help.

 

[Steve Winograd [MVP]]

[snip]
First, thanks for the extremely fast reply. Now the details...

NIC1 (Equipment) 10.1.1.100
NIC2(House Network via DHCP) 172.20.30.42

Both currently use subnet mask 255.255.255.0. I've changed the subnet mask
for NIC1 to 255.0.0.0. The equipment is trying access the 172.20.30.42
address instead of the 10.1.1.100. The two pieces of equipment are
10.1.1.101 and 102.

I've attached the route table. Thanks again.

Active Routes:
Network Destination Netmask Gateway Interface Metric
0.0.0.0 0.0.0.0 172.20.30.2 172.20.30.42 20
10.0.0.0 255.0.0.0 10.1.1.100 10.1.1.100 20
10.1.1.100 255.255.255.255 127.0.0.1 127.0.0.1 20
10.255.255.255 255.255.255.255 10.1.1.100 10.1.1.100 20
127.0.0.0 255.0.0.0 127.0.0.1 127.0.0.1 1
172.20.30.0 255.255.255.0 172.20.30.42 172.20.30.42 20
172.20.30.42 255.255.255.255 127.0.0.1 127.0.0.1 20
172.20.255.255 255.255.255.255 172.20.30.42 172.20.30.42 20
172.21.17.152 255.255.255.255 172.20.30.1 172.20.30.42 1
224.0.0.0 240.0.0.0 10.1.1.100 10.1.1.100 20
224.0.0.0 240.0.0.0 172.20.30.42 172.20.30.42 20
255.255.255.255 255.255.255.255 10.1.1.100 10.1.1.100 1
255.255.255.255 255.255.255.255 172.20.30.42 172.20.30.42 1
Default Gateway: 172.20.30.2

Thanks for the additional information. I see one unusual thing in the
route table: the second line shows that NIC1 has its own IP address as
its default gateway.

The default gateway is the address of a router elsewhere on the
network that has a connection to other subnets (such as the Internet)
for use when an IP address isn't on the local network. Remove the
default gateway specification from NIC1.

I don't see anything else that could cause a problem in network
access. However, I don't understand what the problem is that you're
seeing. Please the problem in as much detail as possible, including:

1. What is the equipment software trying to access?

2. How is the equipment software trying to access it?

3. How do you know that it's using the wrong IP address or network?

4. What would be happening if everything worked right? How would you
know?

4. What happens if you disable the house network and try using the
equipment software?

I will try removing the gateway from NIC1 next week as I am out until then.
Also, to answer your questions...

1) When the software is launched, it looks for the two peripheral pieces of
equipment at 10.1.1101 and 102, then checks for the "server" which is the PC
at 10.1.1.100. I found that the subnet mask for the equipment LAN needs to
be 255.255.255.0.

3) You can monitor the software startup in a a status bar as it's loading.
When it gets to the PC IP it says it's trying to access the 172.20.30.42
house address which is incorrect.

4) If everything were operating correctly, the software would launch
successfully and bring up a ready window. As it currently stands, the
software locks up and crashes if it accesses the incorrect IP.

Thanks again for your help.

You're welcome. And thanks for providing more details.

Unfortunately, I don't know anything about the program that you're
running or how it works.

How does the program know where to find the "server"? Do you tell it
the name or the IP address of the "server"?

Does the computer that runs the program have connections to both
networks? Does the "server" have connections to both networks?
--
Best Wishes,
Steve Winograd, MS-MVP (Windows Networking)

Please post any reply as a follow-up message in the news group
for everyone to see. I'm sorry, but I don't answer questions
addressed directly to me in E-mail or news groups.

Microsoft Most Valuable Professional Program
http://mvp.support.microsoft.com

 

[Guest]

The program is "coded" to look for a specific IP, in this case the server (or
PC) at 10.1.1.100. We must enter this specific address for the NIC along
with the subnet mask of 255.255.255.0. The software will lock up if this
entry is different.

The computer has connections to both networks. However, when we remove the
second NIC for the house network, the application runs fine and accesses the
equipment without flaw. It's only when we have the second NIC installed for
the house network that the software has the issues.

Again, I will try removing the gateway address from the house network NIC
next week and see if that helps. Thanks again for your assistance and I was
surprised to see a response over a weekend.

[snip]
First, thanks for the extremely fast reply. Now the details...

NIC1 (Equipment) 10.1.1.100
NIC2(House Network via DHCP) 172.20.30.42

Both currently use subnet mask 255.255.255.0. I've changed the subnet mask
for NIC1 to 255.0.0.0. The equipment is trying access the 172.20.30.42
address instead of the 10.1.1.100. The two pieces of equipment are
10.1.1.101 and 102.

I've attached the route table. Thanks again.

Active Routes:
Network Destination Netmask Gateway Interface Metric
0.0.0.0 0.0.0.0 172.20.30.2 172.20.30.42 20
10.0.0.0 255.0.0.0 10.1.1.100 10.1.1.100 20
10.1.1.100 255.255.255.255 127.0.0.1 127.0.0.1 20
10.255.255.255 255.255.255.255 10.1.1.100 10.1.1.100 20
127.0.0.0 255.0.0.0 127.0.0.1 127.0.0.1 1
172.20.30.0 255.255.255.0 172.20.30.42 172.20.30.42 20
172.20.30.42 255.255.255.255 127.0.0.1 127.0.0.1 20
172.20.255.255 255.255.255.255 172.20.30.42 172.20.30.42 20
172.21.17.152 255.255.255.255 172.20.30.1 172.20.30.42 1
224.0.0.0 240.0.0.0 10.1.1.100 10.1.1.100 20
224.0.0.0 240.0.0.0 172.20.30.42 172.20.30.42 20
255.255.255.255 255.255.255.255 10.1.1.100 10.1.1.100 1
255.255.255.255 255.255.255.255 172.20.30.42 172.20.30.42 1
Default Gateway: 172.20.30.2

Thanks for the additional information. I see one unusual thing in the
route table: the second line shows that NIC1 has its own IP address as
its default gateway.

The default gateway is the address of a router elsewhere on the
network that has a connection to other subnets (such as the Internet)
for use when an IP address isn't on the local network. Remove the
default gateway specification from NIC1.

I don't see anything else that could cause a problem in network
access. However, I don't understand what the problem is that you're
seeing. Please the problem in as much detail as possible, including:

1. What is the equipment software trying to access?

2. How is the equipment software trying to access it?

3. How do you know that it's using the wrong IP address or network?

4. What would be happening if everything worked right? How would you
know?

4. What happens if you disable the house network and try using the
equipment software?

I will try removing the gateway from NIC1 next week as I am out until then.
Also, to answer your questions...

1) When the software is launched, it looks for the two peripheral pieces of
equipment at 10.1.1101 and 102, then checks for the "server" which is the PC
at 10.1.1.100. I found that the subnet mask for the equipment LAN needs to
be 255.255.255.0.

3) You can monitor the software startup in a a status bar as it's loading.
When it gets to the PC IP it says it's trying to access the 172.20.30.42
house address which is incorrect.

4) If everything were operating correctly, the software would launch
successfully and bring up a ready window. As it currently stands, the
software locks up and crashes if it accesses the incorrect IP.

Thanks again for your help.

You're welcome. And thanks for providing more details.

Unfortunately, I don't know anything about the program that you're
running or how it works.

How does the program know where to find the "server"? Do you tell it
the name or the IP address of the "server"?

Does the computer that runs the program have connections to both
networks? Does the "server" have connections to both networks?
--
Best Wishes,
Steve Winograd, MS-MVP (Windows Networking)

Please post any reply as a follow-up message in the news group
for everyone to see. I'm sorry, but I don't answer questions
addressed directly to me in E-mail or news groups.

Microsoft Most Valuable Professional Program
http://mvp.support.microsoft.com

 

[Steve Winograd [MVP]]

The program is "coded" to look for a specific IP, in this case the server (or
PC) at 10.1.1.100. We must enter this specific address for the NIC along
with the subnet mask of 255.255.255.0. The software will lock up if this
entry is different.

The computer has connections to both networks. However, when we remove the
second NIC for the house network, the application runs fine and accesses the
equipment without flaw. It's only when we have the second NIC installed for
the house network that the software has the issues.

Again, I will try removing the gateway address from the house network NIC
next week and see if that helps. Thanks again for your assistance and I was
surprised to see a response over a weekend.

You're welcome.

You don't need to remove the second NIC. You can simply disable the
network connection that uses the second NIC, or unplug the cable from
the second NIC.

I don't know how the program can look for the wrong IP address when
you give it a specific IP address for the server. If you gave the
program the server's name instead, I could understand how it could
look for the wrong IP address: the server's name could resolve to the
IP address of either one of its network connections.

I don't think that removing the invalid default gateway specification
will make any difference. Please report the result.
--
Best Wishes,
Steve Winograd, MS-MVP (Windows Networking)

Please post any reply as a follow-up message in the news group
for everyone to see. I'm sorry, but I don't answer questions
addressed directly to me in E-mail or news groups.

Microsoft Most Valuable Professional Program
http://mvp.support.microsoft.com

 

[Guest]

Problem solved...although I'm still not sure why. Anyway, the fix was to use
a single NIC, plug the house network into a router along with the equipment,
set the NIC to automatically obtain the IP address AND set the alternate
configuration to the SAME IP address, subnet mask, and default gateway that
has already been assigned to the computer. We can now use the equipment and
simultaneously access the house network without any issues. Again thanks for
all of your assistance.

 

[Steve Winograd [MVP]]

Problem solved...although I'm still not sure why. Anyway, the fix was to use
a single NIC, plug the house network into a router along with the equipment,
set the NIC to automatically obtain the IP address AND set the alternate
configuration to the SAME IP address, subnet mask, and default gateway that
has already been assigned to the computer. We can now use the equipment and
simultaneously access the house network without any issues. Again thanks for
all of your assistance.

You're welcome. I'm glad that you were able to find a solution.
Thanks for letting the news group know.
--
Best Wishes,
Steve Winograd, MS-MVP (Windows Networking)

Please post any reply as a follow-up message in the news group
for everyone to see. I'm sorry, but I don't answer questions
addressed directly to me in E-mail or news groups.

Microsoft Most Valuable Professional Program
http://mvp.support.microsoft.com