DHCPNAK reporting "wrong network" sometimes? What is it?

[Hexabion]

What does this mean?

I have some VPN on at times, but they do not use 192.168.*.*
and my LAN uses 10.0.*.*

Jan 19 16:19:34 dnsmasq-dhcp[839]: DHCPNAK(br0) 192.168.1.43 *macaddress* wrong network
Jan 19 16:20:04 dnsmasq-dhcp[839]: DHCPNAK(br0) 192.168.1.73 *macaddress* wrong network
Jan 19 17:26:11 dnsmasq-dhcp[839]: DHCPNAK(br0) 192.168.1.169 *macaddress* wrong address

Where it says "*macaddress*" I have just cut out the mac-address due to security, but it's my deviced confirmed, so not any "unknown" devices at all.


Thanks in advance for any enlightenment.

 

[coldwizard]

Computers remember the last IP address they used. When they connect to a network, they ask if they can continue to use that address. The DHCP server will respond with a NAK (no) or ACK (yes).

If you just connected a computer that was connected somewhere else (like work), then the message is fine, because the saved network address is from there and the computer needs to get one for your network.

If you did not use the computer on another network, then it is possible that you have a second DHCP server on your network. You need to find it and turn it off.

 

[Hexabion]

Computers remember the last IP address they used. When they connect to a network, they ask if they can continue to use that address. The DHCP server will respond with a NAK (no) or ACK (yes).

If you just connected a computer that was connected somewhere else (like work), then the message is fine, because the saved network address is from there and the computer needs to get one for your network.

If you did not use the computer on another network, then it is possible that you have a second DHCP server on your network. You need to find it and turn it off.

Well, that solves that mystery my friend. It so happens to be that all the devices (mac-addresses) in the list are android devices, namely phones, in which connect to... wait for it... waaaaaait for it... my work/office, and then I get home, one thing leads to another and bada bing, the rest is history

Thank you a billion times for such an obvious and simple explanation, I can sleep without paranoia one more night! (I'm sorry the "thanks"-button is only clickable once, but atleast you have a 1:1 ratio of posts and thanks, impressive. )

 

[SeCrEt_BoY]

I have the same problem... And my network just have 1 DHCP is my RT-AC87R...

 

[kevindb]

What problem?

 

[coldwizard]

I have the same problem... And my network just have 1 DHCP is my RT-AC87R...

You already asked and got the answer for this message from Merlin on Thursday.

http://www.snbforums.com/threads/asuswrt-merlin-378-51-is-out.23198/page-12#post-171801

 

[SeCrEt_BoY]

You already asked and got the answer for this message from Merlin on Thursday.

http://www.snbforums.com/threads/asuswrt-merlin-378-51-is-out.23198/page-12#post-171801

But it is not... The MAC is iPhone MAC which is just stay at home. The same with my Note 4... all day I stay at home and systemalog still show wrong network with Note 4 MAC...

Gửi từ SM-N910C của tôi bằng cách sử dụng Tapatalk

 

[coldwizard]

But it is not... The MAC is iPhone MAC which is just stay at home. The same with my Note 4... all day I stay at home and systemalog still show wrong network with Note 4 MAC...

Gửi từ SM-N910C của tôi bằng cách sử dụng Tapatalk

OK, you have checked and only one DHCP server on your network and devices always stay home. No trips outside home with devices.

Does the message always have the same starting IP?
DHCPNAK(br0) 192.168.11.xx

When you do a network scan (or get a list of wifi in your area) from the device do any of the other networks show as open or not secured?

 

[SeCrEt_BoY]

OK, you have checked and only one DHCP server on your network and devices always stay home. No trips outside home with devices.

Does the message always have the same starting IP?
DHCPNAK(br0) 192.168.11.xx

When you do a network scan (or get a list of wifi in your area) from the device do any of the other networks show as open or not secured?

My Network Tree: Fiber - Converter - RT-AC87R -> No more router behind AC87R.
Around my house there are many secure WIFI and I dont know any pass... and there is no open WiFI...



Gửi từ SM-N910C của tôi bằng cách sử dụng Tapatalk

 

[kevindb]

Can we please move on from a default position of 'something is wrong with dnsmasq' to perhaps considering that the DHCP client is buggy. It wouldn't be the first and it most certainly won't be the last.

 

[coldwizard]

My Network Tree: Fiber - Converter - RT-AC87R -> No more router behind AC87R.
Around my house there are many secure WIFI and I dont know any pass... and there is no open WiFI...
Gửi từ SM-N910C của tôi bằng cách sử dụng Tapatalk

Great, that rules out a random connection to nearby router.

Does it happen more than once a day?
Does the message always have the same starting IP address?
DHCPNAK(br0) 192.168.11.xx



@kevindb We are not investigating dnsmasq - Both Merlin and I have said the messages were correct - dnsmasq is working correctly and with no second DHCP server on the network, the messages could be safely ignored. What I am trying to understand is how 2 different devices with no trips outside home can connect to a different dhcp server.

 

[kevindb]

Good

Do we know what these 2 different devices are? As missus dB returned from shopping with her iThing earlier I saw a dhcpnak as it tried to reuse an IP address from when it was out...a thought occurred that if these devices were mobile phones might they be trying to re-use addressed obtained from mobile data access rather than just wifi.

A wire shark on the lan is the only way to be really sure some other device isn't trying to provide dhcp service (eg an over enthusiastic & incorrectly bridge adsl/cable modem.)

 

[coldwizard]

Do we know what these 2 different devices are? As missus dB returned from shopping with her iThing earlier I saw a dhcpnak as it tried to reuse an IP address from when it was out...a thought occurred that if these devices were mobile phones might they be trying to re-use addressed obtained from mobile data access rather than just wifi.

A wire shark on the lan is the only way to be really sure some other device isn't trying to provide dhcp service (eg an over enthusiastic & incorrectly bridge adsl/cable modem.)

Devices are "The MAC is iPhone MAC which is just stay at home. The same with my Note 4... all day I stay at home and system log still show wrong network with Note 4 MAC"

I had dismissed the idea of a mobile data access since I would expect a cell tower would want to handle more than 254 clients and therefore would use a 10.x.x.x (class A address) rather than a 192.168.11.x (class C address).

Rather than using wire shark, we could just turn off the DHCP server on the RT-AC87R and try to re-connect. If a second DHCP server exists, it would assign an address from it's address pool. We would need to assign a static IP address to reach the RT-AC87R to turn on it's DHCP server again.
But I don't think we need to do the test for the DHCP server because secret boy would have problems getting to the Internet during the time his machine are using the wrong DHCP server.

 

[RMerlin]

Could also be a neighbour with an unprotected wireless to which your devices are occasionally connecting to.

 

[coldwizard]

Could also be a neighbour with an unprotected wireless to which your devices are occasionally connecting to.

Asked that question in posting #8/9 this thread. No open devices.

Waiting to hear back if happening daily and same IPs.
If nothing since first few days after upgrade, maybe old configuration was using different DHCP range.