When an interface goes down, any neigbors learnt on that interface

When an interface goes down, any neigbors learnt on that interface
using IPv6 Router Advertisements (RAs) must be deleted. When an
interface comes up and neighbors are learnt on that interface, the
BGP FSM for any interface peer must be started only if a valid
local address exists; the local address may come up later after IPv6
Duplicate Address Detection.