RT-AX router sporadic IP conflicts

[rahman]

Recently switched to an Asus RT-AX88U from a Netgear AX500. I must say the UI/UX on the Asus is far superior; the Netgear had an absolute garbage UI and UX- designed to look cool for people who would never actually use the features. However the Asus has many more network problems.

We recently tested out a few of the other cheaper Asus RT-AX routers as well, which I would assume share much of the same code. This problem happened on them as well so it is definitely firmware related and not a single bad unit. All have been running the latest firmware.


The router keeps trying to assign IPs via DHCP to devices while the same IP is being used as a static IP on another device.

For example one machine has a static of 192.168.1.102 and has always had that IP, but today I notice one of the ESP based IoT devices is offline. I go to the network list and see that that IP is now showing up under the IoT device, with its MAC and device name. The IoT device has no connectivity while the computer still does. This computer is always on btw.

Every few days I have to reset it and then it works for another few days before one device or another starts malfunctioning.

There are no other DHCP servers on the network; and everything worked fine before we got the Asus, and it also works fine most of the time.

Other times it will just randomly refuse to route certain cameras to their dvr server, but they can still be accessed by their app.

We never have more than 55 clients at any one time, most of which are IoT devices and should not be using many resources. I don't know if there is an unofficial maximum number of devices this thing can handle or what- but for such an expensive router it should be able to handle this.

Please advise; thanks!

 

[ColinTaylor]

The router keeps trying to assign IPs via DHCP to devices while the same IP is being used as a static IP on another device.

When you say the devices have a "static IP" what do you mean? Do you mean that the device is not using DHCP but has it's IP manually configured in its network interface? Or do you mean that the device is using DHCP but has an IP reservation created for it in the router's DHCP server?

 

[Tucu]

Have you modified the IP pool range of your DHCP server to exclude the range of addresses that you want to use as static addresses?

 

[rahman]

@ColinTaylor manually configured

@Tucu That has not been necessary on previous routers; every other brand has not tried to assign the DHCP addresses of the static-IP servers.

If that is the problem, why does resetting the router fix the issue temporarily?

 

[ColinTaylor]

@ColinTaylor manually configured

@Tucu That has not been necessary on previous routers; every other brand has not tried to assign the DHCP addresses of the static-IP servers.

If that is the problem, why does resetting the router fix the issue temporarily?

If you have manually set the IP address on the client's network adapter and not changed the DHCP range on the router accordingly you will see this sort of issue. The router has no way of knowing what IP addresses have been set manually on the clients, so it's random chance whether there is a conflict each time a DHCP client connects.

So for example, if you are manually configuring clients in the range 192.168.1.200 - 192.168.1.254 you need to change the router's DHCP range to 192.168.1.2 - 192.168.1.199.

Alternatively, do not manually configure the clients but instead change them to use DHCP and create reserved IP addresses for them on the router (LAN > DHCP Server > Manually Assigned IP...).

 

[rahman]

Seriously this never happened on the Netgear. Asus must assign addresses differently- i.e. randomly pick from the whole pool range, while the Netgear maybe used the upper portion of the 255?

But I get what you're saying. I will manually limit the DHCP range.

The router has no way of knowing what IP addresses have been set manually on the clients

Then why do the static assigned IPs show up in the client list marked as static? I know some routers don't even show you any static clients but this one does.

 

[Tucu]

@ColinTaylor manually configured

@Tucu That has not been necessary on previous routers; every other brand has not tried to assign the DHCP addresses of the static-IP servers.

If that is the problem, why does resetting the router fix the issue temporarily?

Are you sure you didn't have the addresses reserved in your old Netgear?
There are multiple ways you can handle this:
1) configure the DHCP server to have the IPs reserved for the MACs of the devices with fixed IPs, but keep assigning them static addresses. Not ideal, but the DHCP server will not assign those IPs again and will not complain about the client.
2) configure the DHCP server to have the IPs reserved for the MACs of the devices that you want set for fixed IPs, and configure the devices to use dynamic IPs
3) configure the DHCP server pool to leave out a range of addresses and use those for your static ip devices. In my own setup I leave a block of 20 or so free for devices like APs and switches that I like using static addresses

 

[avtella]

No even I stopped reserving IPs in the router and simply fixed them client side (ie NAS & Ooma) long back, generally no issues on Netgear routers and now on pfSense, they simply don’t try to use those IPs as the router does know those clients are connecting with said IPs.

However I agree with the others just try setting up reservation router side and it’s probably also a better practice as in rare cases when a fixed IP client (that has no reservation) is off /disconnected long enough the router may re-use the IP causing a conflict (especially if this coincided with a router or dhcp service restart) when that client device is turned back on or reconnected, this situation I have faced on rare occasions.

 

[ColinTaylor]

Seriously this never happened on the Netgear. Asus must assign addresses differently- i.e. randomly pick from the whole pool range, while the Netgear maybe used the upper portion of the 255?

The DHCP server assigns new IP addresses pseudo-randomly from across the whole DHCP range based on a hash of the client's MAC address.

Then why do the static assigned IPs show up in the client list marked as static? I know some routers don't even show you any static clients but this one does.

The client list is dumb (but tries to be clever). If there is a DHCP reservation for a client it says it's "Manual" otherwise it looks at the list of DHCP leases the server has issued and if it finds a match it's shown as "DHCP". For everything else it assumes it to be static. The DHCP server itself has no knowledge of any IP addresses other than those it has issued since the router was turned on.