Configuring LDP with CLI
This section provides information to configure LDP using the command line interface.
Topics in this section include:
LDP Configuration Overview
When the implementation of LDP is instantiated, the protocol is in the no shutdown state. In addition, targeted sessions are then enabled. The default parameters for LDP are set to the documented values for targeted sessions in draft-ietf-mpls-ldp-mib-09.txt.
LDP must be enabled in order for signaling to be used to obtain the ingress and egress labels in frames transmitted and received on the service distribution path (SDP). When signaling is off, labels must be manually configured when the SDP is bound to a service.
Basic LDP Configuration
This chapter provides information to configure LDP and remove configuration examples of common configuration tasks.
The LDP protocol instance is created in the no shutdown (enabled) state.
The following displays the default LDP configuration.
Common Configuration Tasks
This section provides information to configure:
Enabling LDP
LDP must be enabled in order for the protocol to be active. MPLS does not need to be enabled on the router except if the network interface uses the Packet over Sonet (POS) encapsulation (Sonet path encapsulation type set to ppp-auto). In this case, MPLS must be enabled and the interface name added into MPLS to allow for the MPLSCP to come up on the PPP link between the two peers and for MPLS to be used on the interface. MPLS is enabled in the config>router>mpls context.
Use the following syntax to enable LDP on a router:
The following displays the enabled LDP configuration.
Configuring FEC Originate Parameters
A FEC can be added to the LDP IP prefix database with a specific label operation on the node. Permitted operations are pop or swap. For a swap operation, an incoming label can be swapped with a label in the range of 16 to 1048575. If a swap- label is not configured then the default value is 3.
A route table entry is required for a FEC with a pop operation to be advertised. For a FEC with a swap operation, a route-table entry must exist and user configured next-hop for swap operation must match one of the next-hops in route-table entry.
Use the following syntax to configure FEC originate parameters:
The following displays a FEC originate configuration example.
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 recovery is self-contained and relies on information stored internally to self-heal. This feature is only used to help third-party routers without a self-healing capability to recover.
Maximum recovery time is the time (in seconds) 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) the LSR is willing to retain its MPLS forwarding state. The time should be long enough to allow the neighboring LSRs to re-sync all the LSPs in a graceful manner, without creating congestion in the LDP control plane.
Use the following syntax to configure graceful-restart parameters:
Applying Export and Import Policies
Both inbound and outbound label binding filtering are supported. Inbound filtering allows a route policy to control the label bindings 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:
- Neighbor — Match on bindings received from the specified peer.
- Interface — Match on bindings received from a neighbor or neighbors adjacent over the specified interface.
- Prefix-list — Match on bindings with the specified prefix/prefixes.
Outbound filtering allows a route policy to control the set of LDP label bindings advertised by the LSR. An export policy can control the set of LDP label bindings advertised by the router. By default, label bindings for only the system address are advertised and propagate all FECs that are received. All other local interface FECs can be advertised using policies.
 | Note:
The system IP address and static FECs cannot be blocked using an export policy. |
Matches can be based on:
- Loopback — loopback interfaces.
- All — all local subnets.
- Match — match on bindings with the specified prefix/prefixes.
Use the following syntax to apply import and export policies:
The following displays export and import policy configuration examples.
Targeted Session Parameters
Use the following syntax to specify targeted-session parameters:
The following example displays an LDP configuration example:
Interface Parameters
Use the following syntax to configure interface parameters:
The following example displays an interface parameter configuration example:
Session Parameters
Use the following syntax to specify interface parameters:
The following example displays an LDP configuration example:
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 distribution paths (SDPs) are configured, extended discovery mechanisms enable LDP to send periodic targeted hello messages to the SDP far-end point. The exchange of LDP hellos trigger session establishment. The SDP signaling default enables tldp. The service SDP uses the targeted-session parameters configured in the config>router>ldp>targeted-session context.
The SDP LDP and LSP commands are mutually exclusive; either one LSP can be specified or LDP can be enabled. If LDP is already enabled on an MPLS SDP, then an LSP cannot be specified on the SDP. If an LSP is specified on an MPLS SDP, then LDP cannot be enabled on the 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 more information about configuring SDPs, refer to the SR OS Services Guide.
The following example displays the command syntax usage to configure enable LDP on an MPLS SDP:
The following displays an example of an SDP configuration showing the signaling default tldp enabled.
The following displays an example of an SDP configuration for the 7750 SR, showing the signaling default tldp enabled.
The following shows a working configuration of LDP over RSVP-TE (1) where tunnels look like the second example (2):
Example 1: LDP over RSVP-TE
Example 2: Tunnels
LDP Configuration Management Tasks
This section discusses the following LDP configuration management tasks:
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 command syntax to disable LDP:
Modifying Targeted Session Parameters
The modification of LDP targeted session parameters does not take effect until the next time the session goes down and is re-establishes. Individual parameters cannot be deleted. The no form of a targeted-session parameter command reverts modified values back to the default. Different default parameters can be configured for IPv4 and IPv6 LDP targeted hello adjacencies.
The following example displays the command syntax usage to revert targeted session parameters back to the default values:
The following output displays the default values:
Modifying Interface Parameters
Individual parameters cannot be deleted. The no form of a interface-parameter command reverts modified values back to the defaults. The modification of LDP targeted session parameters does not take effect until the next time the session goes down and is re-establishes.
The following output displays the default values: