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Label Assignment and Distribution. Introducing MPLS Label Allocation, Distribution, and Retention Modes. Outline. Overview Label Distribution Parameters Distributing Labels Allocating Labels Retaining Labels Summary. Label Distribution Parameters.
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Label Assignment and Distribution Introducing MPLS Label Allocation, Distribution, and Retention Modes
Outline • Overview • Label Distribution Parameters • Distributing Labels • Allocating Labels • Retaining Labels • Summary
Label Distribution Parameters • Frame-mode MPLS architecture defines several label allocation and distribution parameters: • Per-platform label space • Unsolicited downstream label distribution • Independent label allocation control • Liberal label retention
Label Distribution: Unsolicited Downstream • The label for a prefix is allocated and advertised to all neighbor LSRs, regardless of whether the neighbors are upstream or downstream LSRs for the destination.
Label Allocation: Independent Control • An LSR can always assign a label for a prefix, even if it has no downstream label. • Independent control can be used only for LSRs with Layer 3 capabilities.
Label Retention: Liberal Retention Mode • Each LSR stores the received label in its LIB, even when the label is not received from a next-hop LSR. • Liberal label retention mode improves convergence speed.
Summary • There are four MPLS label distribution parameters: label space, label distribution, label allocation, and label retention. • Frame-mode MPLS distributes labels using downstream unsolicited label distribution • Frame-mode MPLS allocates labels to neighbors using independent control • Frame-mode MPLS uses liberal label retention