© 2006 Cisco Systems, Inc. All rights reserved. MPLS v2.2—2-1 Label Assignment and Distribution Introducing MPLS Label Allocation, Distribution, and Retention Modes

© 2006 Cisco Systems, Inc. All rights reserved. MPLS v2.2—2-2 Outline Overview Label Distribution Parameters Distributing Labels Allocating Labels Retaining Labels Summary

© 2006 Cisco Systems, Inc. All rights reserved. MPLS v2.2—2-3 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 v2.2—2-4 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 v2.2—2-5 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 v2.2—2-6 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 v2.2—2-7 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 v2.2—2-8