5.11. LDP Command Reference

This command administratively disables an entity. When disabled, an entity does not change, reset, or remove any configuration settings or statistics.

The operational state of the entity is disabled as well as the operational state of any entities contained within. Many objects must be shut down before they can be deleted.

The no form of this command administratively enables an entity.

Unlike other commands and parameters where the default state is not indicated in the configuration file, the shutdown and no shutdown states are always indicated in system-generated configuration files.

This command enables the context to configure an LDP protocol instance.

When an LDP instance is created, the protocol is enabled (in the no shutdown state). To suspend the LDP protocol, use the shutdown command. Configuration parameters are not affected.

The no form of the command deletes the LDP protocol instance, removing all associated configuration parameters. The LDP instance must first be disabled with the shutdown command before being deleted.

This command enables LDP to use the aggregate prefix match function rather than requiring an exact prefix match.

When this command is enabled and an LSR receives a FEC-label binding from an LDP neighbor for a prefix-address FEC element, FEC1, it will install the binding in the LDP FIB if:

When the FEC-label binding has been installed in the LDP FIB, LDP programs an NHLFE entry in the egress data path to forward packets to FEC1. LDP also advertises a new FEC-label binding for FEC1 to all its LDP neighbors.

When a new prefix appears in the RIB, LDP checks the LDP FIB to determine if this prefix is a closer match for any of the installed FEC elements. If a closer match is found, this may mean that the LSR used as the next hop will change; if so, the NHLFE entry for that FEC must be changed.

When a prefix is removed from the RIB, LDP checks the LDP FIB for all FEC elements that matched this prefix to determine if another match exists in the routing table. If another match exists, LDP must use it. This may mean that the LSR used as the next hop will change; if so, the NHLFE entry for that FEC must be changed. If another match does not exist, the LSR removes the FEC binding and sends a label withdraw message to its LDP neighbors.

If the next hop for a routing prefix changes, LDP updates the LDP FIB entry for the FEC elements that matched this prefix. It also updates the NHLFE entry for the FEC elements.

The no form of this command disables the use of the aggregate prefix match function. LDP then only performs an exact prefix match for FEC elements.

This command specifies the policy name containing the prefixes to be excluded from the aggregate prefix match function. Against each excluded prefix, LDP performs an exact match of a specific FEC element prefix, rather than a longest prefix match of one or more LDP FEC element prefixes, when it receives a FEC-label binding or when a change to the prefix occurs in the routing table.

The no form of this command removes all policies from the configuration; therefore, no prefixes are excluded.

This command specifies export route policies that determine which routes are exported to LDP neighbors. Configuring an export policy allows the LSR (Label Switch Router) to advertise addresses other than the system IP address. Policies are configured in the config>router>policy-options context. Refer to the “Route Policies” section in the 7705 SAR Router Configuration Guide.

If no export policy is specified, non-LDP routes will not be exported from the routing table manager to LDP, and only LDP-learned routes will be exported to LDP neighbors.

If multiple policy names are specified, the policies are evaluated in the order they are specified. The first policy that matches is applied. If multiple export commands are issued, the last command entered will override the previous command. A maximum of five policy names can be specified. The specified names must already be defined.

The no form of the command removes all policies from the configuration.

This command enables LDP Fast Reroute (FRR). LDP FRR provides local protection for an LDP FEC by precalculating and downloading a primary and a backup NHLFE for the FEC to the LDP FIB.

When LDP FRR is enabled and an LFA backup next hop exists for the FEC prefix in the RTM, or for the longest prefix the FEC prefix matches to when the aggregate-prefix-match option is enabled, LDP will program the data path with both a primary NHLFE and a backup NHLFE for each next hop of the FEC.

The backup NHLFE is enabled for each affected FEC next hop when any of the following events occurs:

The tunnel-down-damp-time command, when enabled, does not cause the corresponding timer to be activated for a FEC as long as a backup NHLFE is still available.

Because LDP can detect the loss of a neighbor/next hop independently, it is possible that it will switch to the LFA next hop while the IGP (OSPF or IS-IS) is still using the primary next hop. As well, when the interface for the previous primary next hop is restored, the IGP may reconverge before LDP completes the FEC exchange with its neighbor over that interface. This may cause LDP to deprogram the LFA next hop from the FEC and blackhole traffic. In order to avoid this situation, IGP-LDP synchronization should be enabled on the LDP interface with the config>router>if>ldp-sync-timer command (refer to the 7705 SAR Router Configuration Guide, “IP Router Command Reference”, for information on configuring the ldp-sync-timer).

This command adds a FEC to the LDP prefix database with a specific label operation on the node.

Permitted operations are swap to originate a FEC for which the LSR is not egress or pop to originate a FEC for which the LSR is egress.

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, 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 the user-configured next hop for the swap operation must match one of the next hops in the route-table entry.

The next-hop, advertised-label, and swap-label parameters are optional. If a next-hop is configured but no swap-label is specified, the swap occurs with label 3 (implicit null), then the label is popped and the packet is forwarded to the next hop. If the next-hop and swap-label parameters are configured, a regular swap occurs. If no parameters are specified, a pop and forwarding is performed.

This command enables graceful restart helper.

The no form of the command disables graceful restart.

This command configures the local maximum recovery time, which 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.

The no form of the command returns the default value.

This command configures the neighbor liveness time, which 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.

The no form of the command returns the default value.

This command specifies import route policies that determine which routes are accepted from LDP neighbors. Policies are configured in the config>router>policy-options context. Refer to the “Route Policies” section in the 7705 SAR Router Configuration Guide.

If no import policy is specified, LDP accepts all routes from configured LDP neighbors. Import policies can be used to limit or modify the routes accepted and their corresponding parameters and metrics.

If multiple policy names are specified, the policies are evaluated in the order they are specified. The first policy that matches is applied. If multiple import commands are issued, the last command entered will override the previous command. A maximum of five policy names can be specified. The specified names must already be defined.

The no form of the command removes all policies from the configuration.

This command configures the hold time. This is the time interval to wait before declaring a neighbor down. The factor parameter derives the hello interval.

Hold time is local to the system and is sent in the hello messages to the neighbor. Hold time cannot be less than three times the hello interval. The hold time can be configured globally (applies to all LDP interfaces) or per interface. The most specific value is used.

When an LDP session is being set up, the hold time is negotiated to the lower of the two peers. Once an operational value is agreed upon, the hello factor is used to derive the value of the hello interval.

The no form of the command:

This command configures the time interval, in seconds, that LDP waits before tearing down the session. The factor parameter derives the keepalive interval.

If no LDP messages are exchanged for the configured time interval, the LDP session is torn down. Keepalive timeout is usually three times the keepalive interval. To maintain the session permanently, regardless of the activity, set the value to zero.

When an LDP session is being set up, the keepalive timeout is negotiated to the lower of the two peers. Once a operational value is agreed upon, the keepalive factor is used to derive the value of the keepalive interval.

The no form of the command:

This command allows interoperability with third-party legacy IPv4 LSR implementations that do not comply with RFC 5036 with respect to the processing of Hello TLVs with the U-bit set.

The command is a global LDP configuration that disables the Nokia proprietary Interface Info TLV (0x3E05) in the Hello message sent to the peer. Disabling this Hello TLV also results in the non-generation of the Nokia proprietary Hello Adjacency Status TLV (0x3E06) because the Interface Info TLV is not sent.

This command enables the mLDP fast upstream switchover feature.

When this command is enabled and LDP is resolving an mLDP FEC received from a downstream LSR, it checks whether an ECMP next hop or an LFA next hop to the root LSR node exists. If LDP finds one, it programs a primary ILM on the interface corresponding to the primary next hop and a backup ILM on the interface corresponding to the ECMP or LFA next hop. Then, LDP sends the corresponding labels to both upstream LSR nodes. Under normal operation, the primary ILM accepts packets while the backup ILM drops them. If the interface or the upstream LSR of the primary ILM goes down, causing the LDP session to go down, the backup ILM starts accepting packets.

In order to make use of the ECMP next hop, the user must configure the ecmp value in the system to at least “2”, using the following command:

config>router>ecmp

In order to make use of the LFA next hop, the user must enable LFA using the following commands (as needed):

config>router>isis>loopfree-alternate

config>router>ospf>loopfree-alternate

Enabling the IP FRR or LDP FRR feature is not strictly required since LDP only needs to know the location of the alternate next hop to the root LSR so it can send the Label Mapping message to program the backup ILM at the initial signaling of the tree. Therefore, enabling the LFA option is sufficient. However, if unicast IP and LDP prefixes need to be protected, then these features and the mLDP fast upstream switchover can be enabled concurrently.

The mLDP FRR fast switchover relies on the fast detection of a loss of an LDP session to the upstream peer to which the primary ILM label had been advertised. It is strongly recommended that the following be performed:

The no form of this command disables fast upstream switchover for mLDP FECs.

This command configures the maximum time a point-to-multipoint transit or bud node must wait before switching over to the new path if the new node does not send an MBB TLV to inform the transit or bud node of the availability of the data plane.

The no form of the command sets the wait time to the default.

This command enables LDP over tunnels.

The no form of the command disables tunneling.

This command configures an LSP destined for this peer to be used for tunneling an LDP FEC over RSVP-TE. A maximum of four RSVP-TE LSPs can be used for tunneling LDP FECs to the T-LDP peer.

It is not necessary to specify any RSVP-TE LSP in this context unless there is a need to restrict the tunneling to selected LSPs. All RSVP-TE LSPs with a to address matching that of the T-LDP peer are eligible by default. The user can also exclude specific LSP names by using the ldp-over-rsvp exclude command in the config>router>mpls>lsp lsp-name context.

The no form of this command removes the LSP association.

This command specifies the time interval, in seconds, that LDP waits before posting a tunnel down event to the Tunnel Table Manager (TTM).

When LDP can no longer resolve a FEC and deactivates it, it deprograms the NHLFE in the data path. It will, however, delay deleting the LDP tunnel entry in the TTM until the tunnel-down-damp-time timer expires. This means that users of the LDP tunnel, such as SDPs (for all services) and BGP (for Layer 3 VPNs), will not be notified immediately. Traffic is still blackholed because the NHLFE has been deprogrammed.

If the FEC gets resolved before the tunnel-down-damp-time timer expires, LDP programs the IOM with the new NHLFE and posts a tunnel modify event to the TTM, updating the dampened entry in the TTM with the new NHLFE information.

If the FEC does not get resolved and the tunnel-down-damp-time timer expires, LDP posts a tunnel down event to the TTM, which deletes the LDP tunnel.

The no form of the command resets the damp timer value back to the default value of 3. If the timer value is set to 0, tunnel down events are not dampened but are reported immediately.

This command enables the context to configure LDP interfaces and parameters applied to LDP interfaces.

This command enables LDP on the specified IP interface.

The no form of the command deletes the LDP interface and all configuration information associated with the LDP interface.

The LDP interface must be disabled using the shutdown command before it can be deleted.

This command enables the use of the address of the link LDP interface as the LSR ID in order to establish an LDP adjacency and session with a directly connected LDP peer.

By default, the LDP session uses the system interface address as the LSR ID unless the LSR ID is explicitly configured. This means that targeted LDP (T-LDP) and interface LDP share a common LDP TCP session and therefore a common LDP label space. The system interface must always be configured on the router or the LDP protocol will not come up on the node.

At initial configuration, the LDP session to the peer remains down while the interface is down. If the user changes the LSR ID while the LDP session is up, LDP immediately tears down the session and attempts to re-establish it using the new LSR ID. If the interface used for the local LSR ID goes down, the LDP session will also go down.

The interface option is the recommended setting when static route-LDP synchronization is enabled.

When the interface option is selected, the transport connection (TCP) for the link LDP session configured by the transport-address command is automatically set to interface. Having both the local-lsr-id and transport address set to the local interface creates two TCP sessions to the peer and therefore two different LDP label spaces: one to the interface IP address for link LDP (L-LDP) and one to the system IP address for T-LDP.

The no form of the command resets the local-lsr-id to the default value.

This command enables or disables multicast traffic forwarding on the interface. The multicast-traffic command must be configured on a per-LDP interface basis to enable point-to-multipoint LDP setup on the interface. Point-to-multipoint LDP must be configured as an inclusive or selective provider tunnel per MVPN to dynamically initiate a point-to-multipoint LSP to the leaf PE nodes learned via NG-MVPN auto-discovery signaling. S-PMSI is for efficient data distribution and is optional.

Use the mldp command to configure point-to-multipoint LDP for an MVPN. The mldp command is found under the config>service>vprn>mvpn>provider-tunnel>inclusive or selective contexts.

This command configures the transport address to be used when setting up the LDP TCP sessions. The transport address can be configured globally (applies to all LDP interfaces) or per interface. The most specific value is used.

With the transport-address command, you can set up the LDP interface to the connection that can be set to the interface address or the system address. However, there can be an issue of which address to use when there are parallel adjacencies. This address selection situation can also occur when there is a link and a targeted adjacency, since targeted adjacencies request the session to be set up only to the system IP address.

The transport-address value should not be interface if multiple interfaces exist between two LDP neighbors.

Depending on the first adjacency to be formed, the TCP endpoint is chosen. In other words, if one LDP interface is set up as transport-address interface and another as transport-address system, then, depending on which adjacency was set up first, the TCP endpoint addresses are determined. After that, because the hello contains the LSR ID, the LDP session can be checked to verify that it is set up and then the adjacency can be matched to the session.

The no form of the command:

This command configures targeted LDP sessions. Targeted sessions are LDP sessions between non-directly connected peers. Hello messages are sent directly to the peer platform instead of to all the routers on this subnet multicast address.

The discovery messages for an indirect LDP session are addressed to the specified peer and not to the multicast address.

This command disables support for targeted sessions. Targeted sessions are LDP sessions between non-directly connected peers. The discovery messages for an indirect LDP session are addressed to the specified peer and not to the multicast address.

The no form of the command enables the setup of any targeted sessions.

This command configures parameters for an LDP peer.

This command enables or disables bidirectional forwarding detection (BFD) tracking of the LDP session for the interface or the T-LDP session for the peer.

The no form of this command disables BFD tracking.

This command enables the use of the address of a specific interface as the LSR ID in order to establish a targeted LDP (T-LDP) adjacency and session with one or more non-directly connected LDP peers. The interface can be a regular interface or a loopback interface, including the system interface.

By default, a T-LDP session uses the system interface address as the LSR ID, unless the LSR ID is explicitly configured. This means that T-LDP and interface LDP share a common LDP TCP session and therefore a common LDP label space. The system interface must be always be configured on the router or the LDP protocol will not come up on the node.

At initial configuration, the LDP session to the peers remains down while the interface is down. If the user changes the LSR ID while the LDP session is up, LDP immediately tears down the session and attempts to re-establish it using the new LSR ID. If the interface used for the local LSR ID goes down, the LDP session to all peers using this LSR ID will also go down.

The user-configured LSR ID is used for extended peer discovery to establish the T-LDP hello adjacency. It is also used as the transport address for the LDP TCP session when it is bootstrapped by the T-LDP hello adjacency. The user-configured LSR ID is not used in basic peer discovery to establish a link-level LDP hello adjacency.

The no form of the command resets the local-lsr-id to the default value, which means that the system interface address is used as the LSR ID.

This command enables the context to configure peer specific parameters.

This command configures parameters for an LDP peer.

This command associates an authentication keychain with LDP. The keychain is a collection of keys used to authenticate LDP messages from remote peers. The keychain allows the rollover of authentication keys during the lifetime of a session and also supports stronger authentication algorithms than clear text and MD5.

The keychain must already be defined in the config>system>security>keychain context.

Either the authentication-key command or the auth-keychain command can be used by LDP, but both cannot be supported at the same time. If both commands are configured, the auth-keychain configuration will be applied and the authentication-key command will be ignored.

By default, authentication is not enabled.

This command specifies the authentication key to be used between LDP peers before establishing sessions. Authentication uses the MD5 message-based digest.

Either the authentication-key command or the auth-keychain command can be used by LDP, but both cannot be supported at the same time. If both commands are configured, the auth-keychain configuration will be applied and the authentication-key command will be ignored.

The no form of this command disables authentication.