Brocade Multi-Service IronWare Multiprotocol Label Switch (MPLS) Configuration Guide (Supporting R05.6.00) - Manual (Page 385)

Multi-Service IronWare Multiprotocol Label Switch (MPLS) Configuration Guide 361
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MPLS LDP-IGP synchronization
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The router can also support LDP GR in helper-only mode. In this mode, a router does not preserve
its forwarding entries on a LDP GR restart, however, it can help a neighboring router recover its
forwarding entries when the neighbor is going through restart.
A NetIron router implementing LDP GR can play one of the two roles:
• A restarting LSR: An LSR that performs LDP restart. A standby MP must be up on a Brocade
MLX series or Brocade NetIron XMR router acting as a restarting LSR for LDP GR to work.
• A GR helper (helper-only mode): An LSR whose neighbor is restarting its LDP component.
NOTE
Brocade MLX series or Brocade NetIron XMR routers can play either role in an LDP GR procedure.
Brocade NetIron CES and Brocade NetIron CER routers support only the helper-only mode.
When LDP GR is enabled on a router, the configuration does not apply to the current sessions. The
LDP GR configuration is applied for the new sessions brought up after the configuration is added.
MPLS failover support for VPLS
VPLS can preserve its forwarding state across MP failover. Therefore, VPLS using LDP tunnels as its
transport mechanism benefits from the LDP GR support. LDP GR recovers both the LDP tunnel
labels and the VC labels for VPLS. This is supported for all local switching traffic as well as traffic
switched between VPLS peers as long as the peer uses LDP tunnels and that LDP GR is configured.
NOTE
When MCT is configured for the VPLS instance involved then VPLS preserving its forwarding state
between the VPLS peers is not guaranteed.
LDP failover support for transit
LDP GR preserves the LDP transit cross-connects. Therefore, it minimizes the traffic loss of any
application that uses an LDP tunnel as its transport mechanism from the transit LSR perspective.
Graceful restart procedure
The following section describes the restart procedures of an LSR and a GR helper LSR.
Procedure for the restarting LSR
After an LSR restarts its LDP components, when its MPLS forwarding state is not preserved (as in
the case of the Brocade NetIron CES and Brocade NetIron CER routers and routers in helper-only
mode), it sends out the FT TLV with Recovery Time set to 0 in the LDP Initialization message to its
neighbor.
When the MPLS forwarding state has been preserved across the restart, the LSR does the
following:
1. Start the Forwarding State Holding timer.
2. Mark all the MPLS forwarding entries as “stale”.
3. Set the Recovery Time to the current value of the Forwarding State Holding timer when it sends
out LDP Initialization message to its neighbor.