An LSR receives and sends label mapping messages for all FECs, resulting in the establishment of a large number of LDP LSPs. The establishment of a large number of LDP LSPs consumes a great deal of LSR resources and as a result, the LSR may be overburdened. An outbound or inbound LDP policy needs to be configured to reduce the number of label mapping messages to be sent or received, reducing the number of LSPs to be established and saving memory.
The outbound LDP policy filters Label Mapping messages to be sent. The outbound LDP policy does not take effect on L2VPN Label Mapping messages, which means that all the L2VPN Label Mapping messages can be sent. In addition, the ranges of FECs to which routes are mapped can be configured separately.
If FECs in the Label Mapping messages to be sent to an LDP peer group or all LDP peers are in the same range, the same outbound policy is applicable to the LDP peer group or all LDP peers.
In addition, the outbound LDP policy supports split horizon. After split horizon is configured, an LSR distributes labels only to its upstream LDP peers.
If no outbound policy is configured, the LSR sends the Label Mapping message.
If an outbound policy is configured, the LSR checks whether the FEC in the Label Mapping message is within the range defined in the outbound policy. If the FEC is within the FEC range, the LSR sends a Label Mapping message for the FEC; if the FEC is not in the FEC range, the LSR does not send a Label Mapping message.
The inbound LDP policy filters the label mapping messages to be received. The inbound LDP policy does not take effect with L2VPN label mapping messages, which means that all L2VPN label mapping messages can be received. In addition, the range of FECs to which the non-BGP routes are mapped is configurable.
If FECs in the label mapping messages to be received by an LDP peer group or all LDP peers are in the same range, the same inbound policy applies to the LDP peer group or all LDP peers.
If no inbound policy is configured, the LSR receives the label mapping message.
If an inbound policy is configured, the LSR checks whether the FEC in the label mapping message is within the range defined in the inbound policy. If the FEC is within the FEC range, the LSR receives the label mapping message for the FEC; if the FEC is not in the FEC range, the LSR does not receive the label mapping message.
If the FEC fails to pass an outbound policy on an LSR, the LSR receives no label mapping message for the FEC.
If a DU LDP session is established between an LSR and its peer, a liberal LSP is established. This liberal LSP cannot function as a backup LSP after LDP FRR is enabled.
If a DoD LDP session is established between an LSR and its peer, the LSR sends a Release message to tear down label-based bindings.