No new hub comes with its own SSID and password. However there is no reason why you cannot change the new Hub SSID and password to the same as previous hub and that way all your wireless devices will connect automatically
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No, it would have totally different details, however you can change them to match your old home hub.
Is the old home hub faulty? If not, then why are you replacing it, as you may encounter other problems if you are upgrading the the BT Smart Hub 2.
Which username and password are you referring to? If you mean the PPPoE broadband login, then nothing changes but the hub manager admin password, the wifi ID and password will all change.
You can change the new hub to have the same SSid (name) and password if you want to keep them so that you do not need to set a new connection all your devices.
If you don't want to do that and are happy to keep the SSid (Name) and password that comes with the hub you will need to make a new connection to it with all your devices.
Thanks for all of the replies. The new hub is in and running fine. I changed the name a pw to match the old one. I have not discarded the old hub, I may use that to extend the range.