Unknown iPhone connected to network

No one can know that remotely. Cross-reference that MAC addy with everything you own and see.

You should first try rebooting your gateway.  If the device is still there, see ifyou can ping it.  If so, and you are absolutely positive it is not one of your devices, change your login and password. 

What will "pinging it" prove ? Suppose it is listed in the section of *allowed devices that are currently offline* / not connected to the network.

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@NoNoBadPuppy wrote:

If it is a rogue device, it will not respond to a ping.

 

Why not ?

 

The MAC address he gave is a valid MAC for an Apple device, per Mac Vendor. 

 

I know. I looked it up yesterday...

 

Since that is the case, the next step would be to see if it responds to a ping. 

 

Still won't prove anything. The only true proof is to cross reference the MAC addy with the actual physical MAC addys of their owned devices and compare them as I stated. It's concrete. Anything else is speculation.

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If it is a rogue device, it will not respond to a ping. If it responds to a ping, it will indicate that it has an active connection on the network.  If the latter, and the OP is sure it is not one of his devices, then the advice to change the login password should be followed.  Yes, I am aware that some devices will not respond to a ping, but it literally only takes a few seconds to ping a device and see if it *does* respond.  The MAC address he gave is a valid MAC for an Apple device, per Mac Vendor.  Since that is the case, the next step would be to see if it responds to a ping. 

I dont get the idea of pinging it.

You did the right thing by checking the MAC address.

If the IP is on your network without permission.

Get it off of your network..

Change your pass to something difficult..

If you have some simple wifi Password 

Like 'Ilovemydogrover' and everyone in your neighbor hood knows you have a dog rover... well bad password.

I am assuming that is not the case.. but just saying..

I think original post mentioned static IPs for your devices. that is a good thing..

My next response would have been to set up access control and static IP's, but I am pretty sure that the user does not have that ability in a rented gateway. 

If devices are assigned static IP's it is easy to see when there is a device that is unrecognized. 

If access control is enabled, devices can be blocked from accessing the network wirelessly, provided the login credentials are changed in case the interloper has guess the password. 

There are a number of reasons that a 'rogue" device might appear on your network...meaning a device that is seen by your router, but it not actually a part of yoru network.  There are many good articles about it on the web, but here is just one of them:

https://appuals.com/fix-unknown-strange-devices-showing-network/

The first step is to determine whether the device is just 'appearing' of is actually attached to the network.  Ping is just one tool to use to determine this. There is nothing wrong with using tools like ping, and arp, to see what is happening on your network.  The amount of time it has taken to type all of these responses took far, far longer than a simple 'ping' and 'arp -a', and tools such as that can help you determine how to proceed.