Hi, There is a way around this..I use a dynamic DNS service. I had the same issues, cameras, ftp and plex servers had issues staying online because every now and then my IP number (public ip) would change and i didnt know the new ip number until i got home. very annoying!
I ended up using a DNS. basically it allows you to create an address like ( joebloggs.mydns.com ) and that stays the same. it acts the same as your ip number but it knows what your public ip number is, so if you isp changes the ip the dns automatically updates the ip address , all you need to use is the dns address so in the camera software when it asks for your external ip number in the settings just type the dns address you created and set up.
i use one and its worked for a couple of years now and ive had several ip number changes. everything works pefectly with it .here is a better explination i found online..
Dynamic DNS, also known as DDNS, solves the problem of ever changing residential IP addresses by associating your address with a consistent domain name without the need to buy a pricey static IP.
Having a home IP address is not as simple as having a business IP address. When you become a residential customer of an ISP, they provide you with an IP address so you can access the internet from your home. However, these dynamic IP addresses frequently change, as the ISP manages their own online systems. This makes it difficult to utilize your residential IP address with other services (webcam, security camera, thermostat, etc.) as the address continues to change without notice.
Thankfully, Dynamic DNS can help by assigning a custom domain name to your home IP address that will update automatically as your home IP continues to change.
All you need to set up a dynamic IP address is a Dynamic DNS host
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