@Mesa Usually, home internet services have dynamic IPs so it usually changes the IP on reboot. You might have to ask your ISP for a static IP. I might be misundersanding this but that's my best guess.

@Mesa Actually, there are quite a few postings regarding people trying to change their IP address.  Simple rebooting their router does not change their IP address.  With DHCP protocol the device (in this case router) should ask for a renewal of the existing IP address on reboot.  The ISP service issued the IP address with a time of life.  As long as the device requests a renewal within that time of life, the IP address should not change.  You can see this in those posts where the person has to leave their router down for 24 hours to get a different IP address.  In my case, either the router is not issuing a renewal and just makes a request for a new IP address on reboot, or Spectrum is changing the IP address despite the renewal request.  Since my last router did not change the IP address on reboot, I thought I would start with asking the Tp-Link team.  Their support is great.   

@Mesa,

Mesa wrote

I thought I would start with asking the Tp-Link team.  Their support is great.   

This is a USER to USER forum. However, some TP-Link employees are here as moderator's and will assist users.

First, what you see 'could' be normal'.

I should also add, I have Spectrum as well, and it is rare when my IP Address changes. Usually when the Internet signal is lost, like in a power outage that thier 'head' is on.

Those 'heads' can handle just so many connections. I understand they try to keep the number of connections to the 'head' below the capability. However, that may not be all of them that can have this done, and they are 'over subscribed'. In that case, when there is a connection made looking for an IP Address, you get the first available. They then drop off one connection that was idle the longest IF all connections are full.

That might not be the situation you are seeing though.

Mesa wrote

In my case, either the router is not issuing a renewal and just makes a request for a new IP address on reboot, or Spectrum is changing the IP address despite the renewal request.  Since my last router did not change the IP address on reboot,

I also think the router does the request at the 1/2 life of the IP Lease time. Not when it expires.

A lot depends on the DHCP server you connect to as well. Some are 'sticky' in that they know what you had and give it back to you, others are not. About the only way I can change mine is to change the MAC Address of my router, so it looks like a new device. I suspect if you put your old router back, it might have a new IP Address now too.

In any event, I suspect this is a question you should be asking Spectrum?

Always possible your router is having a problem, so you might want to actually contact TPL support @ https://www.tp-link.com/us/support/contact-technical-support/ and use either Live or Email and ask them.

Can you get to your NAS using a DDNS?

Also are you using a VPN?

@ArcherC8 No, I need to know the IP address.  It is an additional security feature only allowing one IP address. 

@Mesa 

I use a DDNS service for my security cameras which keeps track of any IP address changes. I can get to the cameras with my iPad or laptop anywhere I have WIFI connection.

In my devices, I use the 'register mode' or 'hostname' instead of the IP mode and enter my previously setup DDNS name. The DDNS name gets updated with the changing IP address either manually, by one of your computers, or by the router. Many router models support DDNS generally for select providers.

I would think most devices would support it. You do not indicate the NAS vendor but here is some info from Synology NAS https://www.synology.com/en-us/knowledgebase/DSM/help/DSM/AdminCenter/connection_ddns

Mesa wrote

@ArcherC8 No, I need to know the IP address.  It is an additional security feature only allowing one IP address. 

@Mesa 

Some ISP's will provide a Fixed IP address to residential customer's (usually for a fee). Others to Business accounts only (and may not provide that to a non-business, and could cost more.

Again, contact your ISP or check its web site for info on that.