I worked at an ISP. The DHCP server we use for our DSL offering was made in the 90s and hasn’t been updated since.
I’ve worked for a few of the larger ISPs in the US. They all have their own special weird shit like a windows NT machine shoved in a corner in a CO in west Texas that you have to remote desktop into and run some java applet from the 90 to log into a hardwired machine from the 70s just to set up a voicemail box for a phone line. Ain’t broke don’t fix it leads to some wild setups at companies you wouldn’t expect it from.
Frankly, I don’t see this a a problem as long as the software is up to date and the hardware is sound. I bet there are thousands of SPARC servers out there processing data 24/7 since 1995.
I don’t know, I remember hearing that everything would soon be IPV6 a couple decades ago.