Enabling LDP

LDP must be enabled in order for the protocol to be active. MPLS must also be enabled. MPLS is enabled in the config>router>mpls context.

Use the following CLI syntax to enable LDP on a 7705 SAR router:

The following example displays the enabled LDP configuration output.

Configuring Graceful Restart Helper Parameters

Graceful Restart Helper advertises to its LDP neighbors by carrying the fault tolerant (FT) session TLV in the LDP initialization message, assisting the LDP in preserving its IP forwarding state across the restart. Alcatel-Lucent’s SAR recovery is self-contained and relies on information stored internally to self-heal.

Maximum recovery time is the time (in seconds) that the sender of the TLV would like the receiver to wait, after detecting the failure of LDP communication with the sender.

Neighbor liveness time is the time (in seconds) that the LSR is willing to retain its MPLS forwarding state. The time should be long enough to allow the neighboring LSRs to resynchronize all the LSPs in a graceful manner, without creating congestion in the LDP control plane.

Use the following syntax to configure graceful restart parameters:

The following example displays the import policy configuration output.

Applying Import and Export Policies

Inbound filtering (import policy) allows a route policy to control the label bindings that an LSR accepts from its peers. An import policy can accept or reject label bindings received from LDP peers. Label bindings can be filtered based on the following:

Outbound filtering (export policy) allows a route policy to control the label bindings advertised by the LSR to its peers. Label bindings can be filtered based on the following:

Import or export policies must already exist before they are applied to LDP. Policies are configured in the config>router>policy-options context. Refer to the “Route Policies” section in the 7705 SAR OS Router Configuration Guide for details.

Note: The 7705 SAR supports a specific number of labels, which varies by platform and software release. If the number of labels is exceeded for a specific protocol (for example, LDP or RSVP), a log message will appear by default in logs 99 and 100. The log message states the affected protocol and the label count that was exceeded. For example: “mpls_label_ilm_helper: XXXX XXX XXXX limit reached max obj count of YYYY”. For the LDP protocol, when the label count is exceeded, LDP sessions will be shut down and all labels will be removed. To recover the LDP sessions, perform a shutdown/no shutdown combination of commands in the config>router>ldp context.

Use the following CLI syntax to apply import or export policies:

The following example displays the import and export policy configuration output.

Configuring Interface Parameters

Use the following CLI syntax to configure LDP interface parameters:

The following example displays the LDP interface parameter configuration output.

Specifying Targeted Session Parameters

Use the following CLI syntax to specify targeted session parameters:

The following example displays the LDP targeted session configuration output.

Specifying Peer Parameters

Use the following CLI syntax to specify LDP peer parameters:

The following example displays the LDP peer parameters configuration output.

Enabling LDP Signaling and Services

When LDP is enabled, targeted sessions can be established to create remote adjacencies with nodes that are not directly connected. When service destination points (SDPs) are configured, extended discovery mechanisms enable LDP to send periodic targeted hello messages to the SDP’s far-end point. The exchange of LDP hellos triggers session establishment. The SDP’s signaling default enables tldp. The SDP uses the targeted-session parameters configured in the config>router>ldp>targeted-session context.

The service>sdp>ldp and router>lsp commands are mutually exclusive; you can either specify an LSP or enable an LDP. There cannot be two methods of transport in a single SDP.

To enable LDP on the SDP when an LSP is already specified, the LSP must be removed from the configuration using the no lsp lsp-name command. For further information about configuring SDPs, refer to the 7705 SAR OS Services Guide.

Use the following CLI syntax to enable LDP on an MPLS SDP:

The following example displays an SDP configuration output with the signaling default tldp enabled.

Disabling LDP

The no ldp command disables the LDP protocol on the router. All parameters revert to the default settings. LDP must be shut down before it can be disabled.

Use the following CLI syntax to disable LDP:

Modifying Targeted Session Parameters

You can modify targeted session parameters without shutting down entities. However, for any LDP timers (hello or keepalive timers), the changes do not take effect until a shutdown/no shutdown command is performed on the LDP session.

The no form of a targeted-session parameter command reverts modified values back to the default.

The following example displays the CLI syntax to revert targeted session parameters back to the default values.

The following example displays the default value output.

Modifying Interface Parameters

You can modify LDP interface parameters without shutting down entities. However, at the global timer configuration level (ldp>interface-parameters), the hello and keepalive parameter modifications do not take effect until a shutdown/no shutdown command is performed on the LDP session. At the interface timer configuration level (ldp>interface-parameters>interface), any changes to the keepalive parameter do not take effect until a shutdown/no shutdown command is performed on the LDP session. For all other parameters, the changes take effect immediately.

Individual parameters cannot be deleted. The no form of an interface-parameter command reverts modified values back to the defaults.

The following example displays the CLI syntax to revert interface parameters back to the default values.

The following example displays the default value output.