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Question: High Sierra and Router DHCP Issues

I’ve purchased two new routers in the past couple of weeks due to the fact that Comcast increased my Internet speed and I needed the new high speed protocols to take advantage of it..


Both routers have crashed due to IP address conflicts... On both routers (one a Netgear, the other a Linksys) my MacBook Pro running High Sierra 10.13.1 has all of a sudden started generating IP address conflict error messages... One message will say the conflict is: “Another unit has 192.168.1.120”, a little later the error message will say: “Another unit has 192.168.1.130”...


Both routers were reset to factory settings multiple times and re configured... Same result.


I‘ve spent a frustrating amount of time on the phone with technical support with no resolution...


I decided maybe the MacBook was the problem so I gave it a dedicated IP address below the DHCP range of the router. So far the router (Linksys AC1750) is happy and all is well...


Anyone have any idea why the macbook is causing problems??

MacBook Pro with Retina display, OS X Yosemite (10.10.2)

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Dec 10, 2017 8:56 AM in response to N7BY In response to N7BY

OK.


That problem is caused because the Mac (and probably other devices as well) really wants to hold onto the IP Address it was using before. So it goes ahead and uses it, and does not ask for a new DHCP Address.


Meanwhile, The Router thinks that address lease has expired, and therefore seems to be free, so the Router passes it out as a new DHCP Address to the next device that needs one.


If your home network devices did not come and go as much you would rarely run into this problem. If you have Network Printers, it is a good idea in general to give them at a fixed IP addresses they way you already described, using an Address "out of line" with the DHCP Addresses.


There was a bug in some Apple software (five years ago or more) that caused a device to hold its DHCP Address across sleep, and when it woke and tried to use the same address, it wreaked havoc on the Network for the same reasons you are describing here. If this is similar bug, you are the first to describe it.


Do you have the Time and Time Zone set correctly on all devices?

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Dec 9, 2017 8:52 PM in response to N7BY In response to N7BY

To use more than one Router on your network, pick ONE that provides DHCP addresses, the other two are set to "Bridge Mode" that is, they do not provide DHCP addresses, but merely act as access points. Then give each Router the same Network-name and password, and you have a working Roaming Network or Wirelessly Extended Network.


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Dec 9, 2017 8:52 PM

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Dec 10, 2017 8:56 AM in response to N7BY In response to N7BY

OK.


That problem is caused because the Mac (and probably other devices as well) really wants to hold onto the IP Address it was using before. So it goes ahead and uses it, and does not ask for a new DHCP Address.


Meanwhile, The Router thinks that address lease has expired, and therefore seems to be free, so the Router passes it out as a new DHCP Address to the next device that needs one.


If your home network devices did not come and go as much you would rarely run into this problem. If you have Network Printers, it is a good idea in general to give them at a fixed IP addresses they way you already described, using an Address "out of line" with the DHCP Addresses.


There was a bug in some Apple software (five years ago or more) that caused a device to hold its DHCP Address across sleep, and when it woke and tried to use the same address, it wreaked havoc on the Network for the same reasons you are describing here. If this is similar bug, you are the first to describe it.


Do you have the Time and Time Zone set correctly on all devices?

Dec 10, 2017 8:56 AM

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Dec 10, 2017 9:00 AM in response to Grant Bennet-Alder In response to Grant Bennet-Alder

Thanks Grant. I’ll check time zones and I think your advice on assigning more static ip addresses is wise... we’ve got 28 devices connected to our router. The network is still working fine so I think that the MacBook Pro/Linksys router we’re not playing well together for whatever reason....

Dec 10, 2017 9:00 AM

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Dec 10, 2017 11:01 AM in response to N7BY In response to N7BY

I have a similar situation on my Home Router. I set up the Printers and secondary Routers with manual addresses way down low in the range, and was using DHCP in the range of 192.168.0.150. So all the Macs got addresses in that range at one time.


They refuse to let go of them.


I changed the DHCP range to start at 192.168.0.101 (up through .250) a few months ago. Not one device has moved to new addresses starting in that range -- they are all sticking with their "original" DHCP Addresses in the 150 range.

Dec 10, 2017 11:01 AM

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Question: High Sierra and Router DHCP Issues