Different MPLS Modes

An LSR can use different modes when distributing labels to other LSRs. This section covers three distinct modes, as follows:

  • Label distribution mode

  • Label retention mode

  • LSP control mode

Each mode has its own characteristics. This section explains the advantages of each.

Label Distribution Modes

The MPLS architecture has two modes to distribute label bindings:

  • Downstream-on-Demand (DoD) label distribution mode

  • Unsolicited Downstream (UD) label distribution mode

In the DoD mode, each LSR requests its next-hop (that is, downstream) LSR on an LSP, a label binding for that FEC. Each LSR receives one binding per FEC only from its downstream LSR on that FEC. The downstream LSR is the next-hop router indicated by the IP routing table. ...

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