78Task Command RemarksPerform MPLS LSP tracert to locateerrors along an MPLS LSP.tracert lsp [ -a source-ip | -expexp-value | -h ttl-value | -rreply-mode |-t time-out ] * ipv4dest-addr mask-length[ destination-ip-addr-header ]Available in any view.When equal-cost LSPs existbetween the ingress node and theegress mode, you cannot use MPLSLSP tracert to locate node errors onthe LSPs.Configuring BFD for LSPsYou can configure BFD to detect the connectivity of an LSP. After the configuration, a BFD session isestablished between the ingress and egress of the LSP, and the ingress will add the label for the FEC intoa BFD control packet, forward the BFD control packet along the LSP to the egress, and determine thestatus of the LSP according to the reply received. Upon detecting an LSP failure, BFD triggers a trafficswitchover.A BFD session for LSP connectivity detection can be static or dynamic.• Static—If you specify the local and remote discriminator values by using the discriminator keywordwhen configuring the bfd enable command, the BFD session is established with the specifieddiscriminator values. Such a BFD session is used to detect the connectivity of a pair of LSPs inopposite directions (one from local to remote, and the other from remote to local) between twodevices.• Dynamic—If you do not specify the local and remote discriminator values when configuring the bfdenable command, the MPLS LSP ping is run automatically to negotiate the discriminator values andthen the BFD session is established based on the negotiated discriminator values. Such a BFDsession is used for connectivity detection of an LSP from the local device to the remote device.Configuration prerequisites• The BFD session parameters configured on the loopback interface whose IP address is configuredas the MPLS LSR ID are used, and the BFD packets use the MPLS LSR ID as the source address.Before enabling BFD for an LSP, you must configure an IP address for the loopback interface andconfigure the IP address as the MPLS LSR ID. You can also configure BFD session parameters for theloopback interface as needed. For more information about BFD, see High AvailabilityConfiguration Guide.• To establish a static BFD session, ensure there is already an LSP from the local device to the remotedevice and an LSP from the remote device to the local device.Configuration guidelines• You cannot establish both a static BFD session and a dynamic BFD session for the same LSP.• After a static BFD session is established, you cannot modify the discriminator values of the BFDsession.• In a BFD session for detecting LSP connectivity, the ingress node always operates in active modeand the egress node always operates in passive mode. The bfd session init-mode command doesnot take effect on the ingress and egress nodes of such a BFD session. Even if you configure the twonodes to both operate in passive mode, the BFD session can still be established successfully.• BFD for MPLS LDP is for detecting the IP connectivity between two remote LDP peers. BFD for LSP isfor detecting the connectivity of LSPs.
