False IP conflict message...?

K

Kenneth

Howdy,

We have six systems, a wireless access point, and a wireless
print server, behind a router.

The WAP, and the WPS have static IP addresses, and the
systems are all DHCP.

On occasion, we get an error on one of the systems saying
that there is a duplicate IP address.

We have checked with care, and it ain't so...

What might be causing the error, and (other than the modest
inconvenience) can I ignore it?

Also, is there a way to find out what the system displaying
the error thinks the problem is specifically?

(I should add that I have checked the event viewer tree, but
it shows nothing relevant. Oddly, the System branch shows a
string of information entries dated 7-9-09 which caused me
to check the system date, which is fine. Weird...)

Thanks for any help,
 
M

Malke

Kenneth said:
Howdy,

We have six systems, a wireless access point, and a wireless
print server, behind a router.

The WAP, and the WPS have static IP addresses, and the
systems are all DHCP.

On occasion, we get an error on one of the systems saying
that there is a duplicate IP address.

We have checked with care, and it ain't so...

What might be causing the error, and (other than the modest
inconvenience) can I ignore it?

Also, is there a way to find out what the system displaying
the error thinks the problem is specifically?

(I should add that I have checked the event viewer tree, but
it shows nothing relevant. Oddly, the System branch shows a
string of information entries dated 7-9-09 which caused me
to check the system date, which is fine. Weird...)
Click to expand...

My guess is that you haven't set the static IP addresses outside of the DHCP
address range. So if your print server, for ex., is 192.168.1.3 and one of
the computers gets 192.168.1.3 before the print server "wakes up" as it
were, you'll get this kind of IP conflict.

Go into your router's configuration utility and check your DHCP range. Set
it to something like 192.168.1.2-192.168.1.149 (obviously substitute your
correct subnet). Then assign static IPs for printers, print servers,
wireless access points, etc. to addresses above that.

Malke
 
K

Kenneth

My guess is that you haven't set the static IP addresses outside of the DHCP
address range. So if your print server, for ex., is 192.168.1.3 and one of
the computers gets 192.168.1.3 before the print server "wakes up" as it
were, you'll get this kind of IP conflict.

Go into your router's configuration utility and check your DHCP range. Set
it to something like 192.168.1.2-192.168.1.149 (obviously substitute your
correct subnet). Then assign static IPs for printers, print servers,
wireless access points, etc. to addresses above that.

Malke
Click to expand...

Hi Malke,

I will certainly give it a try, and thank you for the
suggestion,
 
K

Kenneth

Hi Malke,

I will certainly give it a try, and thank you for the
suggestion,
Click to expand...

Hi again Malke,

Well, it was such a good idea, that I apparently had done it
already:

The router's DHCP range is set to provide 40 addresses
starting from 192.168.1.100.

The two static addresses are 192.168.1.245, and
192.168.1.150, so they are out of range.

Might you have any other thoughts about this?

Thanks again,
 
M

Malke

Kenneth said:
Well, it was such a good idea, that I apparently had done it
already:

The router's DHCP range is set to provide 40 addresses
starting from 192.168.1.100.

The two static addresses are 192.168.1.245, and
192.168.1.150, so they are out of range.

Might you have any other thoughts about this?
Click to expand...

No, I'm sorry but I don't. But hopefully one of the networking gurus will
come around. You might want to check on MVP Jack's site to see if he covers
this.

http://www.ezlan.net

Malke
 
J

Jack \(MVP-Networking\).

Hi
If your Router can do IP reservation within the DHCP (aka Static IP) set it
so that the Wired and Wireless computers that you have onsite would obtain
always the same IP (it usually goes by their MAC number) and would benefit
from being on a DHCP server. This way any additional transient computers
would choose an IP that is Not reserved, and the onsite computers would
always get their personal address. It is also better for the Mapped and
Shared Drives to be on Reserved the IP since they would be always at the
same Network spot.
Jack (MS, MVP-Networking)
 
K

Kenneth

Hi Jack,

Unfortunately, my router will not do the "reserved address"
stuff.

It does seem to me that the error message is spurious, and
it seems not to have caused any difficulty (other than its
occasional appearance), but I would like to learn more about
what might be causing it.

Is there any way that this problem could be caused by
flakiness in the router itself? I ask because in the last
month or so, I have found that, on occasion, one, or more,
of our systems seems to "disappear" from the lan. When we
spot that problem, we have rebooted the router and all has
been well. The router is a Linksys, and I do suspect that it
is entering its last days.

Thanks for your thoughts,
 
K

Kenneth

Hi
Yap, the Linksys line does not do DHCP Reservation.
However if it is a model that can be flashed with DD_WRT you might be able
to flash the firmware have Reservation and infuse new life to the Router.
Look here, http://www.dd-wrt.com/wiki/index.php/Main_Page
Jack (MS, MVP-Networking)
Click to expand...

Hi Jack and All,

I had been having occasional error messages telling me that
two devices on our LAN had the same IP address, but I could
not trace it down because when I looked at each address,
they were, indeed, unique.

Well, it happened again today, but this time, something
showed up in Event Viewer.

It provided the MAC address of the device assigned the IP
address that was in conflict.

('Sounds good so far, huh...?)

Well, I can't find a device with that MAC address. I know
it's out there, but I have not been able to find it.

Is there an approach to this situation that I am missing?

Many thanks for any help,
 
L

Lem

Kenneth said:
Hi Jack and All,

I had been having occasional error messages telling me that
two devices on our LAN had the same IP address, but I could
not trace it down because when I looked at each address,
they were, indeed, unique.

Well, it happened again today, but this time, something
showed up in Event Viewer.

It provided the MAC address of the device assigned the IP
address that was in conflict.

('Sounds good so far, huh...?)

Well, I can't find a device with that MAC address. I know
it's out there, but I have not been able to find it.

Is there an approach to this situation that I am missing?

Many thanks for any help,
Click to expand...

The first six characters of the MAC address identify the device
manufacturer. Perhaps that would help you find it.
http://www.coffer.com/mac_find/

Otherwise ... how is your network protected from intruders?

--
Lem -- MS-MVP

To the moon and back with 2K words of RAM and 36K words of ROM.
http://en.wikipedia.org/wiki/Apollo_Guidance_Computer
http://history.nasa.gov/afj/compessay.htm
 
S

smlunatick

Hi again,

Our 7 systems are behind a router...

(and I will check the site you suggested.)

Many thanks,
Click to expand...

Is this a wireless router?
If yes, does the wireless network have a WiFi security access key
(WEP, WPA or WPA2?) If it does not, you may have someone "piggy-
backing" onto your Internet access.

Also, you might want to check the router's status pages and check to
see what "devices" are currently connected to the router. Check which
are truly yours.
 
K

Kenneth

Is this a wireless router?
If yes, does the wireless network have a WiFi security access key
(WEP, WPA or WPA2?) If it does not, you may have someone "piggy-
backing" onto your Internet access.

Also, you might want to check the router's status pages and check to
see what "devices" are currently connected to the router. Check which
are truly yours.
Click to expand...

Hi again,

The router is not wireless...

I had not thought to check the status page and will do that
later today.

Thanks,
 
K

Kenneth

Hi again,

The router is not wireless...

I had not thought to check the status page and will do that
later today.

Thanks,
Click to expand...

Hi again All,

It took a while, but, I am making progress...

I just got the "System detected an IP address conflict"
error that I had described.

Event viewer told me the MAC address of the hardware with
which there was a conflict.

It was my iPhone.

It had an ip address of 192.168.1.105.

I turned off the iPhone, and looked at the ip address of the
system that displayed the error. It was the same as the
iPhone, 192.168.1.105.

(Things will get stranger in a moment, but...)

I rebooted the iPhone, and it got an ip address of
192.168.1.106. So, at that point, there was no conflict.

Of course, I had no idea how the DHCP could dole out the
same address twice.

Next, with several systems (and the iPhone) on the LAN, I
went into the router's configuration and looked at the DHCP
table.

It showed the system with the original error message as
192.168.1.104, and I thought that I had recalled something
incorrectly (because I remembered it as 192.168.1.105) so I
ran ipconfig, and it showed 192.168.1.105.

At that point the DHCP table did not match the actual
assignments, so I click to refresh the table. The screen
refreshed, but nothing was modified.

With apologies for what may be excessive detail, I am stuck:

The router's DHCP table does not match the reality of the
assignments, and the router apparently assigns addresses
that are already in use.

Is it new router time?

Thanks for any help on this,

Many thanks,
 
J

John Wunderlich

It took a while, but, I am making progress...

I just got the "System detected an IP address conflict"
error that I had described.

Event viewer told me the MAC address of the hardware with
which there was a conflict.

It was my iPhone.

It had an ip address of 192.168.1.105.

I turned off the iPhone, and looked at the ip address of the
system that displayed the error. It was the same as the
iPhone, 192.168.1.105.

(Things will get stranger in a moment, but...)

I rebooted the iPhone, and it got an ip address of
192.168.1.106. So, at that point, there was no conflict.

Of course, I had no idea how the DHCP could dole out the
same address twice.

Next, with several systems (and the iPhone) on the LAN, I
went into the router's configuration and looked at the DHCP
table.

It showed the system with the original error message as
192.168.1.104, and I thought that I had recalled something
incorrectly (because I remembered it as 192.168.1.105) so I
ran ipconfig, and it showed 192.168.1.105.

At that point the DHCP table did not match the actual
assignments, so I click to refresh the table. The screen
refreshed, but nothing was modified.

With apologies for what may be excessive detail, I am stuck:

The router's DHCP table does not match the reality of the
assignments, and the router apparently assigns addresses
that are already in use.

Is it new router time?
Click to expand...

Two things I would do at this point in time:

1) Unplug your router from its power source for several seconds and
repower it. Perhaps it just needs a fresh reset. Power-cycle all
connecting devices as well. My router's DHCP server fails about
every 2 months or so. Power cycling fixes it for another couple of
months.

2) Check the router manufacturer's web site for updated firmware for
the router. This might be a common problem with that make/model of
router that has been corrected with a new firmware load.

HTH,
John
 
S

smlunatick

Hi again All,

It took a while, but, I am making progress...

I just got the "System detected an IP address conflict"
error that I had described.

Event viewer told me the MAC address of the hardware with
which there was a conflict.

It was my iPhone.

It had an ip address of 192.168.1.105.

I turned off the iPhone, and looked at the ip address of the
system that displayed the error. It was the same as the
iPhone, 192.168.1.105.

(Things will get stranger in a moment, but...)

I rebooted the iPhone, and it got an ip address of
192.168.1.106. So, at that point, there was no conflict.

Of course, I had no idea how the DHCP could dole out the
same address twice.

Next, with several systems (and the iPhone) on the LAN, I
went into the router's configuration and looked at the DHCP
table.

It showed the system with the original error message as
192.168.1.104, and I thought that I had recalled something
incorrectly (because I remembered it as 192.168.1.105) so I
ran ipconfig, and it showed 192.168.1.105.

At that point the DHCP table did not match the actual
assignments, so I click to refresh the table. The screen
refreshed, but nothing was modified.

With apologies for what may be excessive detail, I am stuck:

The router's DHCP table does not match the reality of the
assignments, and the router apparently assigns addresses
that are already in use.

Is it new router time?

Thanks for any help on this,

Many thanks,
Click to expand...

Some DHCP service / servers can have a "bug" assigning IPs. Some seem
to require to detect all "assigned" devices before recycling IP
addresses.
 
K

Kenneth

Some DHCP service / servers can have a "bug" assigning IPs. Some seem
to require to detect all "assigned" devices before recycling IP
addresses.
Click to expand...

Hi again,

Would there be something I can do about the problem...?

Thanks,
 
S

smlunatick

Hi again,

Would there be something I can do about the problem...?

Thanks,
Click to expand...

Depending on the DHCP server / unit / service, there might be an
update / fix / firmware upgrade. May or may not "fix" this "bug"
unless the DHCP "maker" had "deemed" that their DHCP is to work that
way.

It would be easier to take note of this previous problem since it can,
and will, re-occur.
 
K

Kenneth

It would be easier to take note of this previous problem since it can,
and will, re-occur.
Click to expand...

Hi again,

With apology, I do not understand your comment above...

Of course, I understand that it might occur again, but what
do you mean by my taking note of it?

Thanks again,
 
S

smlunatick

Hi again,

With apology, I do not understand your comment above...

Of course, I understand that it might occur again, but what
do you mean by my taking note of it?

Thanks again,
Click to expand...

Note which possible "devices" that might get the "same" IP and write
down the steps you did to fix this problem.

Apple is reported to be releasing a revised platform for the iPhone.
I live in Canada, where the only authorized cell carrier of the iPhone
is "over-charging" the plan. Because of this over-charge, it is
rumoured that "only" Canadian Apple Store is refusing to sell the
iPhones.
 

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