Sky hub not seeing all IP addresses

[HKMC]

Our new Sky broadband hub, (new service connected today 27 Mar 2023), is not seeing all the IP addresses on our network. 

Our old Plusnet Hub One had no problem, it saw all the IP addresses automatically.

Does the new Sky hub need configuring to see the whole network?

Grateful for any help

[JPR007]

@HKMC Not quite sure what you mean? The router assigns IP addresses within a network when devices connect, assuming it is being used with DHCP on? The devices don't have there own IP address, unless you are getting confused with MAC addresses?

[HKMC]

Thanks @JPR007.
Yes, I was saying it wrongly. The new Sky Connect hub can't see all the devices on the network.
When I do Windows CMD arp -a  I can see only a small number of devices.
I think that command should show the IP and MAC addresses of all the devices on the network, but lots of them are missing.
All the devices were on the network with the previous Plusnet hub but now they are missing.
What do you think please?

[TimmyBGood · Accepted solution]

@HKMC 

I think that's a subnet mask thing.

A Sky Hub has a default IP address of 192.168.0.1

If it (or the PC you are using) also has a default subnet mask of 255.255.255.0 then the only IP addresses 'visible' will be 192.168.0.0 to 192.168.0.254

Addresses outside that range will not be on the same subnet.

Given Plusnet is really BT its Hub will have been on 192.168.1.254 so devices still using addresses allocated by it are not in a 192.168.0.x / 255.255.255.0 range.  This should be resolved automatically once they renew IP address using DHCP, but if you have anything hard-set in that range you'll need to manually change either them or the Sky Hub.

[HKMC]

Yes @TimmyBGood, that's the problem, thank you.

Both the Sky and Plusnet hubs have subnet mask 255.255.255.0.

So what to do? Should I change the Sky gateway address from 192.168.0.1 to 192.168.1.1 ?

Would this give it the same host address range as the Plusnet gateway? And therefore it would "see" all the devices that were in that IP address range on the Plusnet?

The Plusnet router had a DHCP Network Range of 192.168.1.64 to 192.168.1.253.  We were using 14 of the addresses outside the DHCP range for devices we want as static addresses (from 192.168.1.11 to 192.168.1.24).

Should we try to reserve those static addresses in the Sky router?

[jamesn123]

@HKMC 

Any devices that had a static address assigned with the PlusNet hub need to be changed back to DHCP or you need to change the LAN address space on the Sky hub to 192.168.1.xxx rather than 192.168.0.xxx

[wind-up+merchant]

I'm getting this too.

Would connect everything to a switch help.

[Chrisee]

@wind-up+merchant no adding a switch wont solve network addressing issues indeed managed switches can make them worse.

If you have set your devices to use fixed IP addresses either you need to ef=dit them to fit in the range the Sky hub can "see`' which is 192.268.0.2 to 192.q68.0.254 or change the Hubs LAN I`p settings to match the addess range your devices are in. Other so,ution is set everything to automatic and ghe hub's DHCP server will sort it out.