Packet loss can occur because the actions of the Interior Gateway Protocol (IGP) and the Label Distribution Protocol (LDP)
are not synchronized. Packet loss can occur in the following situations:
When an IGP adjacency is established, the device begins forwarding packets using the new adjacency before the LDP label exchange
completes between the peers on that link.
If an LDP session closes, the device continues to forward traffic using the link associated with the LDP peer rather than
an alternate pathway with a fully synchronized LDP session.
The MPLS LDP IGP Synchronization feature does the following:
Provides a means to synchronize LDP and IGPs to minimize Multiprotocol Label Switching (MPLS) packet loss.
Enables you to globally enable LDP IGP synchronization on each interface associated with an IGP Open Shortest Path First
(OSPF) or Intermediate System-to-Intermediate System (IS-IS) process.
Provides a means to disable LDP IGP synchronization on interfaces that you do not want enabled.
Prevents MPLS packet loss due to synchronization conflicts.
Works when LDP is enabled on interfaces using either the
mpls ip or
mpls ldp autoconfig command.
To enable LDP IGP synchronization on each interface that belongs to an OSPF or IS-IS process, enter the
mpls ldp sync command. If you do not want some of the interfaces to have LDP IGP synchronization enabled, issue the
no mpls ldp igp sync command on those interfaces.
If the LDP peer is reachable, the IGP waits indefinitely (by default) for synchronization to be achieved. To limit the length
of time the IGP session must wait, enter the
no mpls ldp igp sync holddown command. If 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 max-metric on that link.