Igp Synchronization - Cisco ASR 9000 Series Configuration Manual

IGP Synchronization

running using targeted hello adjacency (through R2). When the direct link comes back up, there is no change
in the LDP session state and LDP can converge quickly and begin forwarding MPLS traffic.
Figure 6: Session Protection
Note When LDP session protection is activated (upon link failure), protection is maintained for an unlimited
period time.
Related Topics
Configuring Session Protection, on page 38
Configuring LDP Session Protection: Example, on page 55
IGP Synchronization
Lack of synchronization between LDP and IGP can cause MPLS traffic loss. Upon link up, for example, IGP
can advertise and use a link before LDP convergence has occurred; or, a link may continue to be used in IGP
after an LDP session goes down.
LDP IGP synchronization synchronizes LDP and IGP so that IGP advertises links with regular metrics only
when MPLS LDP is converged on that link. LDP considers a link converged when at least one LDP session
is up and running on the link for which LDP has sent its applicable label bindings and received at least one
label binding from the peer. LDP communicates this information to IGP upon link up or session down events
and IGP acts accordingly, depending on sync state.
In the event of an LDP graceful restart session disconnect, a session is treated as converged as long as the
graceful restart neighbor is timed out. Additionally, upon local LDP restart, a checkpointed recovered LDP
graceful restart session is used and treated as converged and is given an opportunity to connect and
resynchronize.
Under certain circumstances, it might be required to delay declaration of resynchronization to a configurable
interval. LDP provides a configuration option to delay declaring synchronization up for up to 60 seconds.
LDP communicates this information to IGP upon linkup or session down events.
Cisco ASR 9000 Series Aggregation Services Router MPLS Configuration Guide, Release 4.3.x
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Implementing MPLS Label Distribution Protocol
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