The IGP-LDP synchronization and the static route to LDP synchronization features are modified to operate on a dual-stack IPv4/IPv6 LDP interface as follows:
If the router interface goes down or both LDP IPv4 and LDP IPv6 sessions go down, IGP sets the interface metric to maximum value and all static routes with the ldp-sync option enabled and resolved on this interface are de-activated.
If the router interface is up and only one of the LDP IPv4 or LDP IPv6 interfaces goes down, no action is taken.
When the router interface comes up from a down state, and one of either the LDP IPv4 or LDP IPv6 sessions comes up, IGP starts the sync timer at the expiry of which the interface metric is restored to its configured value. All static routes with the ldp-sync option enabled are also activated at the expiry of the timer.
Because of the above behavior, it is recommended that the user configures the sync timer to a value which allows enough time for both the LDP IPv4 and LDP IPv6 sessions to come up.