Label Assignment and Distribution Introducing MPLS Label Allocation

Outline • Overview • Label Distribution Parameters • Distributing Labels • Allocating Labels •

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 © 2006 Cisco Systems, Inc. All rights reserved. MPLS v 2. 2— 2 -3

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. © 2006 Cisco Systems, Inc. All rights reserved. MPLS v 2. 2— 2 -4

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. © 2006 Cisco Systems, Inc. All rights reserved. MPLS v 2. 2— 2 -5

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. © 2006 Cisco Systems, Inc. All rights reserved. MPLS v 2. 2— 2 -6

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 © 2006 Cisco Systems, Inc. All rights reserved. MPLS v 2. 2— 2 -7