3.9. 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 may be deleted.

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.

The no form of this command places an entity in an administratively enabled state.

This command enables the context to configure LDP parameters. LDP is not enabled by default and must be explicitly enabled (no shutdown).

To suspend the LDP protocol, use the shutdown command. Configuration parameters are not affected. The LDP instance must first be disabled using the shutdown command before being deleted.

The no form of this command deletes the LDP protocol instance, removing all associated configuration parameters.

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

When this command is enabled, LDP performs the following procedures for all prefixes. When an LSR receives a FEC-label binding from an LDP neighbor for a specific FEC1 element, it installs 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 routing table, LDP inspects the LDP FIB to determine if this prefix is a closer match for any of the installed FEC elements. For any FEC for which this is true, LDP may have to update the NHLFE entry for this FEC.

When a prefix is removed from the routing table, 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, it updates the NHLFE entry. If not, it sends a label withdraw message to its LDP neighbors to remove the binding.

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 these FEC elements.

The no form of this command disables the use of the aggregate prefix match function and deletes the configuration. LDP then performs only exact prefix matching 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 this prefix occurs in the routing table.

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

This command specifies the export route policies that determine which routes are exported to LDP. Policies are configured in the config>router>policy-options context.

If no export policy is specified, non-LDP routes are not exported from the routing table manager to LDP, and LDP-learned routes are exported only to LDP neighbors. The currenty implementation of the export policy (outbound filtering) can be used only to add FECs for label propagation. The export policy does not control propagation of FECs that an LSR receives from its 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 overrides the previous command. A maximum of five policy names can be specified. Specified names must already be defined.

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

This command enables LDP Fast-Reroute (FRR). When enabled, LDP uses both the primary next hop and LFA next hop, when available, for resolving the next hop of an LDP FEC against the corresponding prefix in the routing table. This results in LDP programming a primary NHLFE and a backup NHLFE into the forwarding engine for each next hop of a FEC prefix for the purpose of forwarding packets over the LDP 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 or the label-withdrawal-delay command, when enabled, do 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 IGP is still using the primary next hop. Also, when the interface for the previous primary next hop is restored, 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. To avoid this situation, IGP-LDP synchronization should be enabled on the LDP interface.

When the SPF computation determines there is more than one primary next hop for a prefix, it does not program an LFA next hop in RTM. The LDP FEC will resolve to the multiple primary next hops that provide the required protection.

The no form of this command disables LDP FRR.

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.

The next-hop, advertised-label, and swap-label keywords are optional. If next-hop is configured but no out-label is specified, a swap occurs with label 3, such as, pop and forward to the next hop. If the next-hop and swap-label are configured, a regular swap occurs. If no parameters are specified, a pop and route is performed.

This command enables graceful restart helper.

The no form of this command disables graceful restart.

This command enables the implicit null label. Use this command to signal the IMPLICIT NULL option for all LDP FECs for which this node is the egress LER.

The no form of this command disables the signaling of the implicit null label.

This command configures the local maximum recovery time.

The no form of this command reverts to the default value.

This command configures the neighbor liveness time.

The no form of this command reverts to the default value.

This command configures import route policies to determine which label bindings (FECs) are accepted from LDP neighbors. Policies are configured in the config>router>policy-options context.

If no import policy is specified, LDP accepts all label bindings 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 overrides the previous command. A maximum of five policy names can be specified. The specified names must already be defined.

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

This command configures the time interval, in seconds, that LDP will delay the withdrawal of the FEC-label binding it distributed to its neighbors when FEC is deactivated. When the timer expires, LDP then sends a label withdrawal for the FEC to all its neighbors. This is applicable only to LDP transport tunnels (IPv4 prefix FECs) and is not applicable to pseudowires (service FECs).

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

If no LDP messages are exchanged for the configured amount of time, 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 the LDP session is being set up, the keepalive timeout is negotiated to the lower of the two peers. When a operational value is agreed upon, the keepalive factor derives the value of the keepalive interval. The session needs to be flapped for the new settings to work.

The no form of this command at the interface level sets the timeout and factor to the values defined under the interface-parameters level.

The no form of this command at the peer level sets the timeout and factor to the values defined under the targeted-session level.

This command enables the use of the address of a specific interface as the LSR ID for the hello adjacency of a T-LDP session. 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; however, the system interface must always be configured on the router or the LDP protocol will not come up on the node. There is no requirement to include the system interface in any routing protocol.

At initial configuration, the T-LDP session remains down while the specified interface is down. LDP does not try to bring it up using the system interface.

If the LSR ID is changed on the fly while the T-LDP session is up, LDP immediately tears down the session and attempts to establish one using the new LSR ID, regardless of the operational state of the new interface.

If the interface used as the LSR ID goes down, the T-LDP session also goes down.

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

The no form of this command reverts to the default behavior, in which case the system interface address is used as the LSR ID.

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

This command enables and disables IPv4 prefix FEC capability on the interface.

This command configures 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 sent in the hello messages to the neighbor. Hold time cannot be less than three times the hello interval.

When LDP session is being set up, the hold-down time is negotiated to the lower of the two peers. After a operational value is agreed upon, the hello factor is used to derive the value of the hello interval. The session needs to be flapped for the new settings to operate.

The no form of this command at the targeted-session level sets the hello timeout and the hello factor to the default values.

The no form of this command at the peer level sets the hello timeout and the hello factor to the value defined under the targeted-session level.

This command enables the suppression of periodic targeted hello messages between LDP peers after the targeted LDP session is brought up.

When this feature is enabled, the target hello adjacency is brought up by advertising the hold-time value that the user configured in the hello timeout parameter for the targeted session. The LSR node starts advertising an exponentially increasing hold-time value in the hello message as soon as the targeted LDP session to the peer is up. Each new incremented hold-time value is sent in several hello messages equal to the value of the argument factor (the dampening factor) before the next exponential value is advertised. This functionality provides time for the two peers to settle on the new value. When the hold-time reaches the maximum value of 0xffff (binary 65535), the two peers send hello messages at a frequency of every [(65535-1)/local helloFactor] seconds for the lifetime of the targeted-LDP session; for example, if the local hello factor is three (3), hello messages are sent every 21844 seconds.

The LSR node continues to compute the frequency of sending the hello messages based on the minimum of its local hold-time value and the one advertised by its peer, as in RFC 5036. For the targeted LDP session to suppress the periodic hello messages, both peers must bring their advertised hold-time to the maximum value. If one of the LDP peers does not, the frequency of the hello messages sent by both peers continues to be governed by the smaller of the two hold-time values.

When the user enables the hello-reduction command on the LSR node while the targeted LDP session to the peer is operationally up, the change takes effect immediately. The LSR node starts advertising an exponentially increasing hold-time value in the hello message, starting with the currently configured hold-time value.

When the user disables the hello-reduction command while the targeted LDP session to the peer is operationally up, the change in the hold-time from 0xffff (binary 65535) to the user-configured value for this peer takea effect immediately. The local LSR immediately advertises the user-configured hold-time value and does not wait until the next scheduled time to send a hello to make sure the peer adjusts its local hold timeout value.

In general, any configuration change to the parameters of the T-LDP hello adjacency (modifying the hello adjacency hello timeout or factor, enabling or disabling hello-reduction, or modifying the hello-reduction factor) causes the LSR node to immediately trigger an updated hello message with the updated hold-time value without waiting for the next scheduled time to send a hello.

The no form of this command disables hello reduction.

This command enables LDP on the specified IP interface. The LDP interface must be disabled using the shutdown command before it can be deleted.

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

This command enables tracking of the hello adjacency to an LDP peer using BFD.

When this command is enabled on an LDP interface, LDP registers with BFD and starts tracking the LSR ID of all peers it formed hello adjacencies with over that LDP interface. The LDP hello mechanism determines the remote address to be used for the BFD session. The parameters used for the BFD session, that is, transmit-interval, receive-interval, and multiplier, are those configured under the IP interface in the config router interface bfd command.

When multiple links exist to the same LDP peer, a hello adjacency is established over each link and a separate BFD session is enabled on each LDP interface. If a BFD session times out on a specific link, LDP immediately associates the LDP session with one of the remaining hello adjacencies and triggers the LDP FRR procedures. As soon as the last hello adjacency goes down because of BFD timing out, the LDP session goes down and the LDP FRR procedures are triggered.

Note: For more information about the list of protocols that support BFD, see 7210 SAS-D, Dxp, K 2F1C2T, K 2F6C4T, K 3SFP+ 8C Router Configuration Guide.

The no form of this command disables BFD on the LDP interface.

This command enables the context to configure IPv4 LDP parameters for the interface.

This command configures the transport address used when setting up LDP TCP sessions. The transport address can be configured as interface or system. 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, users set up the LDP interface to the connection that can be set to the interface address or 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, because 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 formed, the TCP endpoint is chosen. If one LDP interface is set up as transport-address interface and another as transport-address system, 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.

For any specific ILDP interface, as the local-lsr-id parameters is changed to interface, the transport-address configuration loses effectiveness, because it is ignored and the ILDP session always uses the relevant interface IP address as the transport address even though system is chosen.

The no form of this command at the global level reverts the transport address to the default value.

The no form of this command at the interface level sets the transport address to the value defined under the global level.

This command enables the context to configure peer-specific parameters.

This command configures parameters for an LDP peer.

This command configures the export prefix policy to local addresses advertised to this peer.

Policies are configured in the config>router>policy-options context. A maximum of five policy names can be specified. The specified names must already be defined.

The no form of this command removes the policy from the configuration.

This command configures the export route policy used to determine which prefixes received from other LDP and T-LDP peers are redistributed to this LDP peer via the LDP/T-LDP session to this peer. A prefix that is filtered out (deny) is not exported. A prefix that is filtered in (accept) is exported.

If no export policy is specified, all FEC prefixes learned are exported to this LDP peer. This policy is applied in addition to the global LDP policy and targeted session policy.

Policies are configured in the config>router>policy-options context. A maximum of five policy names can be specified. The peer address must be the peer LSR ID address. The specified names must already be defined.

The no form of this command removes the policy from the configuration.

This command enables the context to configure FEC type capabilities for the session or interface.

This command enables or disables IPv4 prefix FEC capability on the session or interface.

This command configures whether LDP provides translation between non-compliant FEC 129 Cisco formats. Peer LDP sessions must be manually configured towards the non-compliant Cisco PEs.

When enabled, Cisco non-compliant format is used to send and interpret received label release messages. The FEC129 SAII and TAII fields are reversed.

The no form of this command disables use and support of Cisco non-compliant forms. The peer address must be the peer LSR ID address.

This command configures the import FEC prefix policy to determine which prefixes received from this LDP peer are imported and installed by LDP on this node. If resolved, these FEC prefixes are then redistributed to other LDP and T-LDP peers. A FEC prefix that is filtered out (deny) is not imported. A FEC prefix that is filtered in (accept) is imported.

If no import policy is specified, the node imports all prefixes received from this LDP/T-LDP peer. This policy is applied in addition to the global LDP policy and targeted session policy. Policies are configured in the config>router>policy-options context. A maximum of five policy names can be specified. The peer address has to be the peer LSR ID address. The specified names must already be defined.

The no form of this command removes the policy from the configuration.

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 SDP triggered automatic generated 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 this command enables the set up of any targeted sessions.

This command configures parameters for an LDP peer.

This command enables LDP over tunnels.

The no form of this command disables tunneling.

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

It is not necessary to specify an RSVP LSP in this context unless there is a need to restrict the tunneling to selected LSPs. All RSVP 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 configure>router>mpls>lsp context.