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Label Assignment and Distribution

Label Assignment and Distribution. Introducing Convergence in Frame-Mode MPLS. Outline. Overview What Is the MPLS Steady-State Operation? What Happens in a Link Failure? What Is the Routing Protocol Convergence After a Link Failure? What Is the MPLS Convergence After a Link Failure?

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Label Assignment and Distribution

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  1. Label Assignment and Distribution Introducing Convergence in Frame-Mode MPLS

  2. Outline • Overview • What Is the MPLS Steady-State Operation? • What Happens in a Link Failure? • What Is the Routing Protocol Convergence After a Link Failure? • What Is the MPLS Convergence After a Link Failure? • What Actions Occur in Link Recovery? • Summary

  3. Steady-State Operation Description • Occurs after the LSRs have exchanged the labels, and the LIB, LFIB, and FIB data structures are completely populated

  4. Link Failure Actions • Routing protocol neighbors and LDP neighbors are lost after a link failure. • Entries are removed from various data structures.

  5. Routing Protocol Convergence • Routing protocols rebuild the IP routing table and the IP forwarding table.

  6. MPLS Convergence • The LFIB and labeling information in the FIB are rebuilt immediately after the routing protocol convergence, based on labels stored in the LIB.

  7. MPLS Convergence After a Link Failure • MPLS convergence in frame-mode MPLS does not affect the overall convergence time. • MPLS convergence occurs immediately after the routing protocol convergence, based on labels already stored in the LIB.

  8. Link Recovery Actions • Routing protocol neighbors are discovered after link recovery.

  9. Link Recovery Actions: IP Routing Convergence • IP routing protocols rebuild the IP routing table. • The FIB and the LFIB are also rebuilt, but the label information might be lacking.

  10. Link Recovery Actions:MPLS Convergence • Routing protocol convergence optimizes the forwarding path after a link recovery. • The LIB might not contain the label from the new next hop by the time the IGP convergence is complete. • End-to-end MPLS connectivity might be intermittently broken after link recovery. • Use MPLS TE for make-before-break recovery.

  11. Summary • MPLS is fully functional when the LIB, LFIB, and FIB tables are populated. • Overall network convergence is dependent upon the IGP. • Upon a link failure, entries are removed from several routing tables. • MPLS convergence after link failure in a frame-mode network does not affect overall convergence time. • MPLS data structures after link failure may not contain updated data by the time the IGP convergence is complete.

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