Brocade Multi-Service IronWare Multiprotocol Label Switch (MPLS) Configuration Guide (Supporting R05.6.00) - Manual (Page 386)

362 Multi-Service IronWare Multiprotocol Label Switch (MPLS) Configuration Guide
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MPLS LDP-IGP synchronization
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When the timer is not expired the LSR uses the labels and next-hop information received from the
neighbor to lookup and clear the stale flag for the corresponding label-FEC entries. When the timer
is expired, all the entries that are still marked as “stale” are deleted and the LDP GR procedure is
completed.
Procedure for the GR helper LSR
When the LSR detects that its LDP session with a neighbor went down and the neighbor is capable
of preserving its forwarding state, the LSR does the following:
1. Retain the label-FEC bindings received by way of the session and mark them as “stale”.
2. Start the Reconnect timer with the timeout value set to the lesser of the peer FT Reconnect
Timeout and the locally configured maximum Reconnect timeout.
3. Attempt to re-establish LDP session with the neighbor using the normal LDP procedure.
All the stale label-FEC bindings are deleted when either condition is true:
• The Reconnect timer has expired and the LDP session to the neighbor is not established.
• LSR receives FT TLV in the Initialization message from the neighbor and the FT Recovery Time
is set to 0.
After the session is re-established, the LDP GR helper resends Label Mappings to its neighbor. For
the stale label-FEC bindings received from the neighbor, they are recovered during the recovery
period which is set to the lesser of the peer Recovery Timeout and the locally configured maximum
recovery time. If the stale entries are not recovered after the Recovery Timer has expired, they are
deleted.
Session down detection on GR helper
A LDP GR enabled router goes into helper-only mode (GR helper) when any of the following events
occur on the router’s neighbors.
• MP failover occurs
• HLOS upgrade occurs
• Remove and re-add of the MPLS configuration
• TCP communication broken (such as, session KeepAlive timer expires)
• UDP communication broken (i.e. adjacency goes down)
• Restarting LDP component by disabling and enabling the loopback
• Restarting a LDP session by issuing the clear mpls ldp neighbor command
In helper-only mode, the LDP GR procedure works at the session level. Any of the above events
causes the helper to detect session down and start the GR procedure. The operation of the GR
helper is the same independent of what has happened on the restarting LSR that triggers the GR
procedure.