68To configure the LDP label distribution control mode:Step Command Remarks1. Enter system view. system-view N/A2. Enter MPLS LDP view. mpls ldp N/A3. Specify the label distributioncontrol mode.label-distribution { independent |ordered }Optional.Ordered by default.For LDP sessions existing before thecommand is configured, you mustreset the LDP sessions for thespecified label distribution controlmode to take effect.4. Enable label re-advertisementfor DU mode. du-readvertise Optional.Enabled by default.5. Set the interval for labelre-advertisement in DU mode. du-readvertise timer value Optional.30 seconds by default.Configuring LDP loop detectionLSPs established in an MPLS domain may be looping. The LDP loop detection mechanism can detectlooping LSPs and prevent LDP messages from looping forever.LDP loop detection can be in either of the following modes:1. Maximum hop countA label request message or label mapping message carries information about its hop count, whichincrements by 1 for each hop. When this value reaches the specified limit, LDP considers that aloop is present and terminates the establishment of the LSP.2. Path vectorA label request message or label mapping message carries path information in the form of pathvector list. When such a message reaches an LSR, the LSR examines the path vector list of themessage for its MPLS LSR ID. If its MPLS LSR ID is not in the list, the LSR adds its LSR ID to the pathvector list. If it is in the list, the LSR considers that a loop has occurred and terminates theestablishment of the LSP.The path vector mode also limits the number of hops of an LSP. An LSR also terminates theestablishment of an LSP when the hop count of the path, or the length of the path vector, reachesthe upper limit.Configuration guidelines• The loop detection modes configured on two LDP peers must be the same for setting up an LDPsession.• To implement loop detection in an MPLS domain, you must enable loop detection on every LSR inthe MPLS domain.• Configure loop detection before enabling LDP capability on any interface.• All loop detection configurations take effect for only the LSPs established after the configurations.Changing the loop detection settings does not affect existing LSPs. You can perform the reset mplsldp command in user view, so the loop detection settings also take effect for existing LSPs.
