I submitted the following as a feature request. Any feedback, support or improvements to the idea are welcome.

When ipv6 is used with a pd and addresses are assigned to interfaces with the from-pool option, the assignment seems totally random. Is there a way there could be a preferred address option (could be read only) that is used by ros so that on reboots each subnet will have more of a sticky assignment for the interface?

Sometimes the interfaces start up so quickly they try to pull the same address from the pool and get stuck in an invalid state. By implementing this option, it works really address two issues. If the pd had changed, then the preferred address would not be used.

Being able to specify an address within the prefix would be useful, e.g. you may wish to use a prefix for devices on a particular VLAN.

For example if you could assign ::10:0:0:0:1/64 to the interface vlan10 and ::23:0:0:0:1/64 to the interface vlan23 and were delegated 2001:DB8:CAFE::/48 the addresses on those interfaces would become 2001:DB8:CAFE:10:0:0:0:1/64 and 2001:DB8:CAFE:23:0:0:0:1/64

I think that would help if you have a static (or fairly static) larger delegation. In my case I get a /60 from comcast and it can change (not often, but it can), so the /48 prefix example would not work in my situation. I am just looking for delegation stickiness when assigning addresses/prefixes from a pool.

The hint method would work with a /60 too. With ::1:0:0:0:1/64 assigned to one interface and ::2:0:0:0:1/64 assigned to a second interface and delegated 2001:DB8:CAFE:BAD0::/60 the addresses on those interfaces would become 2001:DB8:CAFE:BAD1::1/64 and 2001:DB8:CAFE:BAD2::1/64 - you get the same address unless the delegated prefix changes.

It could - just a bit more work on the programming side since the ::1:0:0:0:1/64 etc would need to calculate the source PD and then determine how to apply the value. With a /48 it could be a literal assignment. Perhaps the command could be written as ::{1}:0:0:0:1/64 etc to determine if it is a literal or calculated assignment.

It doesn't have to be anything complicated, it can simply take received subnet and add as many bits as possible from defined address. And it's up to you as user to not go overboard and stick with low numbers, if you suspect that you can receive small(er) prefix.