My question is somewhat related to this question: What ISP needs to provide in order to route native IPv6 /56 range to several VLANs Where that question focused on the private side of a router, my question focuses on the public side and is related to how an ISP performs its job.
Let's assume that my ISP has given me an IPv6 network prefix of 2001:db8:beef:a700::/56. Let's assume I don't subnet it - I simply place my router's LAN interface in that subnet. Let's assume the WAN interface of my router has address 2001:db8:face:2000::2/64 (assigned via DHCP), with an upstream gateway of 2001:db8:face:2000::1. When the upstream gateway gets a packet with a destination address of 2001:db8:beef:a700::abcd from the public Internet, it must route that packet to my router at 2001:db8:face:2000::2. How does the upstream gateway learn that this is what it must do?
This question is being asked with these assumptions:
- The customer equipment is not running any dynamic routing protocols. I haven't seen customer equipment running routing protocols, so I must assume that the upstream gateway has learned of the 2001:db8:beef:a700::/56 network through some other means. What means might that be?
- The DHCPv6 server that is handing out prefixes is not running on the upstream gateway. Instead, the upstream gateway is performing DHCP relay. This allows a single DHCP server to serve many networks that may be associated with neighborhoods or towns.
I attempted to test this with some Linux hosts and pfSense routers, but I was unable to replicate the functionality that ISPs provide. I more than welcome corrections to misconceptions I may have developed while learning IPv6.