IPv6 multihoming on MikroTik RouterOS: active/standby failover between two ISPs
TL;DR: I wanted IPv6 failover between two ISPs on a MikroTik RB5009. Announcing two prefixes via SLAAC technically works, but failover is slow because Router Advertisement lifetimes don't expire on demand, and LAN clients can't see upstream routing decisions anyway. As an interim workaround, a PPPoE down script that bounces the DHCPv6-PD client forces RouterOS to deprecate the dead prefix immediately, which gets failover down to about a second. The cleaner approaches are conditional Router Advertisements (RFC 8475) or Source Address Dependent Routing with RFC 8028–aware hosts (RFC 8678). Neither is a native turnkey feature on consumer/SMB gear, but both are reachable on RouterOS through scripting and policy routing, with caveats. The setup I recently bought a MikroTik RB5009UPr to replace my primary FTTH ISP's router and optics. It also replaced a PoE switch, letting me reclaim some desk space. It really is a sweet bit of kit. I then had a second fiber line from an...