MPLS LDP-IGP synchronization also provides the following benefits:
Provides a means to disable LDP-IGP synchronization on interfaces that you do not want enabled
Allows you to globally enable LDP-IGP synchronization on each interface associated with an IGP Open Shortest Path First (OSPF) or IS-IS process. OSPF and IS-IS each operate independently.
MPLS LDP-IGP synchronization may be enabled on an interface or globally. LDP determines convergence (receipt of all labels) for a link through one of two methods:
Receive Label silence mechanism
End Of Lib mechanism (RFC 5919)
The following figure provides an example of LDP-IGP synchronization.
Example with LDP-IGP
synchronization
When the LDP peer is not reachable, the IGP establishes the adjacency to enable the LDP session to be established. When an IGP adjacency is established on a link but LDP-IGP Synchronization is not yet achieved or is lost, the IGP advertises the maximum metric (max-metric) on the link.
Configuration Considerations
Supports only point-to-point interfaces but not tunnel interfaces
On IS-IS, wide metric-style is required
When enabled on IS-IS, the feature applies to both level-1 and level-2 metrics
