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windows7 computer NIC doesn't work with LINUX network

Posted on 2014-11-17
Medium Priority
Last Modified: 2014-12-05
in my company i have 2 networks:
1. regular LAN (windows)
2 LAB (linux servers with dhcp)

The networks are totally separated,
lately people who tried to connect to the LAB network were getting "IP conflict" messages from the NIC although the IP addresses were given by the LAB network DHCP.
also when they tried to configure a static IP address on the NIC it was not possible.

few important issues:
1. it happens only with the LINUX network
2. in the past (2 weeks ago) it didn't happen
3. LINUX computers and XP computers that are trying to connect doesn't suffer from this problem

which bring me to the conclusion that it probably happened because of some windows update that was send lately
does anybody knows something about this problem ?
Question by:sikadmin
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LVL 84

Expert Comment

by:Dave Baldwin
ID: 40446746
It is Not a problem between Linux and Windows, it is a problem with how your network is set up.  If you have two sources for DHCP, you may want to make sure that they are using different IP segments so they won't ever give out the same address.  For example, make one use and the other to be  The first will give out IPs from to and the second will provide IPs from to

Author Comment

ID: 40446760
Hello and thank you for the quick response.
we have two different DHCP segments for the networks:
LAN: 192.168.42.xx
lab 192.168.0.xx

also your answer doesn't explain why LINUX and XP computers work.
and also this problem happens when the computer is connected only to LAB network not to both.
LVL 32

Expert Comment

ID: 40446783
and also this problem happens when the computer is connected only to LAB
- servers should have static IP addresses
- your DHCP device have no idea from what network came DHCP request - so DHCP gives IP address from wrong subnet

you need to have way to tell DHCP server from which subnet request came from - in Cisco world it is ip helper-address <ip-address-of-DHCP-server> set on subnet - to convert DHCP request (broadcast) to unicast so DHCP knows from which network (ip address of default gateway for that network)
But, anyhow, to resolve this issue you need to get settings of your DHCP server, or you need to change setings of some of your network devices.
on Cisco for example this should be
Interface VLAN 50
ip address x.x.x.x y.y.y.y
ip helper-address z.z.z.z
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Author Comment

ID: 40446787
few questions:
if what you are saying is the problem i should have problems with all of my computers, and currently it works fine for LINUX and XP computers
Also it worked perfectly for all computers until ~ 2 weeks ago

also when i set a static IP on the WIN7 computer  (for example:, the NIC doesn't accept the static address when in LAB network
LVL 72

Expert Comment

ID: 40446795
How should a NIC be able to reject that IP? What is the message?
LVL 32

Expert Comment

ID: 40446796
Not all. If you have 2 subnets.
Just one subnet would be affected, other one will always work fine, since all addresses will be given from that range. That is in case that if wrong IP is appearing on one subnet.

NIC will always accept static address (from my experience - I never heard  or had case that NIC won't accept static IP). But can NIC communicate with that address with rest of network that is question.

AND for this part "IP conflict"
Your problem look like you have mix of static and DHCP addresses, but you did not exclude static IP addresses from IP range on DHCP server. So DHCP thinks he can lease addresses that are already statically assigned.
Just few days ago I had that situation.

Author Comment

ID: 40446813
each time i set a fixed IP... the NIC throws a "IP conflict" message although we know that the IP is not taken (by checking the lease list on the Linux DHCP server.

also why i don't experience any of the problems i mentioned in XP and Linux computers ?
if the problems was in the subnet of DHCP MIX, etc. ...shouldn't everyone suffer regardless to the type of OS ?
LVL 84

Expert Comment

by:Dave Baldwin
ID: 40446892
You wrote '," which describe a network segment with 512 addresses.  Most networks in that range use ",".   You can have some problems if the network mask (the second set of numbers) is not the same for all computers on that network.

I have Windows XP and Vista here along with Linux and Mac on the same network without any problems.  The computers I use for web servers have static IP addresses and I leave the ones I rarely use to connect thru DHCP.  My network segment is and I started the static IP address at and went up from there.  

That leaves the DHCP part to be from to and I haven't had any problems except a few years ago I found out that I had accidentally set the network mask on of the computers to "" instead of "".  That moves the 'broadcast' address to a different IP so it wasn't communicating properly with the other computers.  It worked fine after I fixed that.
LVL 32

Expert Comment

ID: 40446893
each time i set a fixed IP... the NIC throws a "IP conflict" message although we know that the IP is not taken (by checking the lease list on the Linux DHCP server).
OK. DHCP lease list won't show static IP addresses.
Try to ping that address, if it is unreachable then something strange is happening.

When NIC asks IP address from DHCP server it is standardized process. There should be no difference if it is  Windows or Linux. -- covers range - - so both subnets are in same range in this case

DHCP Lease Process Overview

    The DHCP client requests an IP address by broadcasting a DHCPDiscover message to the local subnet.

    The client is offered an address when a DHCP server responds with a DHCPOffer message containing an IP address and configuration information for lease to the client. If no DHCP server responds to the client request, the client sends DHCPDiscover messages at intervals of 0, 4, 8, 16, and 32 seconds, plus a random interval of between -1 second and 1 second. If there is no response from a DHCP server after one minute, the client can proceed in one of two ways:

        If the client is using the Automatic Private IP Addressing (APIPA) alternate configuration, the client self-configures an IP address for its interface.

        If the client does not support alternate configuration, such as APIPA, or if IP auto-configuration has been disabled, the client network initialization fails.

    In both cases, the client begins a new cycle of DHCPDiscover messages in the background every five minutes, using the same intervals as before (0, 4, 8, 16, and 32 seconds), until it receives a DHCPOffer message from a DHCP server.

    The client indicates acceptance of the offer by selecting the offered address and broadcasting a DHCPRequest message in response.

    The client is assigned the address and the DHCP server broadcasts a DHCPAck message in response, finalizing the terms of the lease.

When the client receives acknowledgment, it configures its TCP/IP properties by using the DHCP option information in the reply, and completes its initialization of TCP/IP.

In rare cases, a DHCP server might return a negative acknowledgment to the client. This can happen if a client requests an invalid or duplicate address. If a client receives a negative acknowledgment (DHCPNack), the client must begin the entire lease process again.
LVL 72

Expert Comment

ID: 40446967
DHCP leases *do* show static IPs if in their range and detected, that is if they were tried to give out via DHCP, but the test ping to confirm it is unused succeeded. However, that is nothing to rely on, so the IP can be used elsewhere.

There is also a chance that the same PC is sending out test ping on more than one (virtual) NIC, getting each other responses. Or some device (router) sending back the packet.

You need to decide whether you want to use two static IP addresses (best with the same last octett to keep things simple), one for each network, or use a single combined network. In no case you may have a router involved (this includes a L3 switch acting as router).

Author Comment

ID: 40446979
this happened also in a computer with one active NIC and a static IP address.

Thank you all,

i will check your answers and get back to you

Author Comment

ID: 40447116
what i have described above is not happening because a problem in network mix or overlapping,
it happnes also when the computer is connected only to one NIC to LAB
the range of static IP is separated from the range of the dynamic IP
and still we get a duplicate IP notification altough when you ping that IP it doesn't respond...

Accepted Solution

sikadmin earned 0 total points
ID: 40472467
the issue was resolved after Microsoft update release last week...
i still think it was a Microsoft update issue that was fixed with another update
thank you all for your help !

Author Closing Comment

ID: 40482486
nothing else solved the bug,
the bug was solved probably after Microsoft solved it by a new update

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