Thanks for your reply! This seems like the best approach. I'm going ahead with this.Attempting to control IPv4 vs. IPv6 precidence by advertising prefixes on the local LAN is not the way to achieve this, off-link prefix information options are not route information options. To advertise some routes with no default the regular RA lifetime would be zero and there would be RIO options for each route per RFC4191, I don't believe Mikrotik have implemented this.I am still not sure how to convince the routing tables on laptops etc. to only route to those three ipv6 address blocks and perfer-v4 otherwise. Perhaps I need to just live with the default route and use firewall to achieve what I want? Maybe I send back an ICMP unreachable for all but the blocks I want to speed up the happy-eyeballs v4 fallback process?
Set up your IPv6 properly to advertise just the local LAN subnet and gateway to clients. Then prevent clients resolving IPv6 addresses so they only use IPv4 (this would require a better DNS proxy than the inbuilt Mikrotik one), or change their prefix policy lists (for Windows netsh interface ipv6, then show/set prefixpolicies). Having an unreachable default route plus the routes to your desired target on the Mikrotik may work, it depends on how the clients network stack handles the ICMP unreachable responses.
Statistics: Posted by evergreen — Wed Dec 13, 2023 7:33 am