We have a router supplied by Google Fiber. According to the router website, its IPv6 address is:
2605:a600:1d84:bec3::1

But in the PingPlotter time line the first hop is to:
2605:a601:aae5:f900::1

The "official" address doesn't appear anywhere as a hop to the destination. The computer is connected by Ethernet cable to the router.

So what is going on here?

Hey Lem3,

I know we've been communicating about this over email the last few days as well but wanted to make sure this was covered here in case anyone else ever has a similar question!

Since we confirmed over email that PingPlotter and traceroute via Command Prompt show the same thing for hop #1, the likely scenario is that your Google Fiber router has different IPv6 addresses for WAN and LAN. PingPlotter and tracert are probably hitting the router's WAN interface and not its LAN interface, which seems common for IPv6 networks.

The way to check this is to log into your router from a web browser and look for something along the lines of Network Status or Advanced Settings to view the WAN and LAN IPv6 addresses. I'd expect you see the WAN listed as what PingPlotter shows as hop #1 and that the LAN is the address Google has on the router website.