madbrain76's profile

Contributor

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46 Messages

Fri, Feb 26, 2021 6:00 PM

XB6 - how to set static DHCP reservation for LAN devices ?

I have the Comcast XB6 xFi gateway configured in router mode. I have the DHCP range set to 10.0.0.2 through 10.0.0.253 . I'm trying to assign (private) static IPs to my (many!) LAN devices.

1) First, I go to "Connected Devices -> Devices"

2) Then I choose a device and click "Edit".

3) Then, I change the configuration from "DHCP" to "Reserved IP", choosing a new, previously unused IP address from the DHCP range, 10.0.0.50

4) I click "Save"

5) I get "Operation in progress" then after a few seconds : "Failure! Please check your inputs."

 

I tried to modify the DHCP range from 10.0.0.2 to 10.0.0.30 .

I repeated steps 1-4 above. Then I get "Reserve IP address is not in valid range: 10.0.0.2 - 10.0.0.30"

I tried another IP address from the range, 10.0.0.4. And now I get again "Failure! Please check your inputs".

 

Does this feature work at all ? And if so how ?

 

Responses

Accepted Solution

jlavaseur

Problem Solver

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615 Messages

7 m ago

Ok, I was looking for the documentation, I found it and I read it wrong, sorry i doing a extra step, this is what you have to do, do your steps you were doing, but, where it says comments, for some reason you have to put something, anything will do, then it will work, sorry for the mistake, I was using my iPhone, and had a setting that randomly changed my MAC address, causing me problems, once you put something in the comments box, it will work from then on, even if you delete the comment, It will remember it for some reason, that's why I thought it was a bug, I just found it odd that it was mandatory that you add a comment for it too work, I don't remember having to do that in the past with other Comcast gateways, I just found this by accident, I had set some in the past, when I look at them, I had added a comment, so there wasn't a obvious problem because it worked 

madbrain76

Contributor

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46 Messages

7 m ago

That didn't work for me. Even after resetting the router, the UI always enforces that the selected "reserved address" must fall in the DHCP range. If not, it is immediately rejected as being outside the range. If inside the range, it just ends up with "Failure! Please check your inputs".

If anyone actually made this feature work, I'd love to know how. It looks completely broken.

 

jlavaseur

Problem Solver

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615 Messages

7 m ago

this is something I wrote for another post, maybe it will help you
static ips and reserved ips each pull from a different ip range, static ips are set manually and can't be in the set dhcp range, reserved ips have to be in the set dhcp range, as far as I know your can only set one or the other, so if you set a static ip, there can never be a conflict, as it's not in the dhcp range, there for the dhcp server can't attempt to assign that ip, I can be wrong but i always did things this way and never had a problem or conflict of any kind,

Also when a device connects and is assigned a dhcp ip, it gets a lease also, so with that lease it reserves that ip for that device for the duration of the lease, I think the default lease duration is 5 days, or there about, you can set the lease duration time in the gateway, so I am not positive, but the lease probably doesn't show up anywhere, so that might be why you get the already assigned error, because there is a lease involved, I personally set the lease time to forever, so the ip never changes, but hey that's just me being lazy

jlavaseur

Problem Solver

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615 Messages

7 m ago

Did you read what I wrote in the other post you were participating in? I tried to explain it the best I could, If you do it right it works just fine 

madbrain76

Contributor

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46 Messages

7 m ago

Yes, I saw it and just responded there, but it was not helpful unfortunately.

jlavaseur

Problem Solver

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615 Messages

7 m ago

Ok, I'll try to explain it better, so your device is connected and the dhcp server assigned a ip from within its range, it also assigns a lease with it, reserving that ip to the device for the duration of the set lease, I think the default is something like 3 to 5 days, you can configure that duration in the gateway, so the dhcp server automatically assigns the ip, so when you try to change it from dhcp to reserved, you can't change the iP, it already has a lease, so of course you get a error, you have to use the ip already assigned with the lease, also you can't manually set a static ip in the dhcp range, so if you want to set a static ip, it has to be a ip not in the dhcp server range, also you have to set that ip on the device before you connect it to the router, if you don't the dhcp server will assign a ip and you can't manually change it, so I believe the router can have something like 256 ips, so I set the dhcp range to accommodate the amount of static ips I need, example, 10.0.0.25 to 10.0.0.200 or similar, so I can assign static ips from 10.0.02 to 10.0.0.25, also you can let the dhcp server assign a IP, set the lease duration to forever, if you don't want to mess with all of this, so to some it up, static ips have a specific range, dhcp ips have a specific range also, they can't be mixed, one or the other, as a side note, this is information I learned many years ago, maybe it has changed over time, but I follow these principles and everything works great for me, hope this helps you

jlavaseur

Problem Solver

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615 Messages

7 m ago

Did you read what I posted here? I tried to explain it better, I had the Xb6 before I got the Xb7, I did what I wrote above, it worked flawlessly

madbrain76

Contributor

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46 Messages

7 m ago

I'm not getting the "already assigned" error.

The UI for the XB6 clearly requires the IP under "Reserved IP" to be in the DHCP range, otherwise it complains that it's outside the range.

If choosing an IP in the range, it gives th "invalid input" error.

Ie. the feature in the UI always fails regardless.

 

Note that we are talking about static IP reservations by DHCP here, what is called "Reserved IP" in the XB6 UI. Ie. the devices themselves are all configured as DHCP clients, but the DHCP server always assigns them the same IP address. 

 

This is different from configuring a client with a static IP, where IP addresses are manually configured on each device.

 

jlavaseur

Problem Solver

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615 Messages

7 m ago

I just explained it better in your other post

jlavaseur

Problem Solver

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615 Messages

7 m ago

Ok so I figured it out, it could possibly be a bug, but it works for me now, I need to test a few things

madbrain76

Contributor

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46 Messages

7 m ago

jlavaseur,

 

FYI, I have the XB6, not the XB7. It's possible the problem only exists on the XB6. It most definitely looks like a bug.

 

jlavaseur

Problem Solver

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615 Messages

7 m ago

I was able to duplicate the problem on my Xb7, same error you received, so I did a bold move and read the documentation provided on my gateway, it detailed how to accomplish what your trying to do, the steps you outlined in this post are similar, but not exactly what is specifically detailed in the documentation, so I followed the documentation and was able to successfully setup a reserved ip in the dhcp server, that being said, I discovered a different way to accomplish the same thing, but a key element is different then in the documentation, I would assume the documentation would be the correct way to do it, I usually use static ips not associated with the dhcp server for a couple of reasons , one if the device is a critical piece of hardware and the dhcp server goes down, you lose the ability to connect to the gateway, whereas a static ip even if the dhcp server goes down or malfunctions, you can still connect, also If my gateway needs to be replaced or factory reset, I would lose my dhcp settings, unless I had them backed up, or was able to transfer them over with the new gateway activation, anyway I hope this helps you out

madbrain76

Contributor

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46 Messages

7 m ago

Can you detail the exact steps you used that work for the "Reserved IP" feature in the admin UI of the XB6 ?

 

I specifically want to set a DHCP reservation. I have >70 devices on my network. I don't want to configure them each manually. I want to leave them all set to DHCP, and manage their IP addresses in a central place, and that's in the router's DHCP table. If I change router, I would have to reconfigure the whole table, but that would still have to be done only in one place vs >70 different places.

 

madbrain76

Contributor

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46 Messages

7 m ago

BTW, I was uable to locate a manual for the XB6. All I found on the comcast web site was a "Getting started" document which does not talk about DHCP settings at all.

 

madbrain76

Contributor

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46 Messages

7 m ago

OMG Thank you ! Putting something in the comment box actually worked. This is a really crazy bug.

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