MPLS LDP IGP Synchronization Explained and Configuration

Why do we need MPLS LDP IGP synchronization

If IGP (Interior Gateway Protocol) adjacency (example OSPF/IS-IS) starts before LDP (Label Distribution Protocol) adjacency when an interface comes up, traffic will start forwarding over the interface to Core MPLS, but LDP labels are not available. The VPN overlay traffic is dropped until LDP adjacency is up and labels are available. To reduce VPN traffic drops when an interface comes up, we need a feature to synchronize IGP with LDP.

What is MPLS LDP IGP synchronization

The MPLS LDP IGP synchronization feature ensures that LDP is fully established before the IGP path
is used for switching.

This feature is supported only on interfaces running Open Shortest Path First (OSPF) or Intermediate
System-to-System (IS-IS) processes.
• This feature works when LDP is enabled on interfaces with either the mpls ip or mpls ldp autoconfig
command.

Configuration

Enables the Multi protocol Label Switching (MPLS) Interior Gateway Protocol (IGP) synchronization for OSPF or IS-IS interfaces, configured under IGP protocol process level:

Device(config-router)# mpls ldp syncCode language: PHP (php)