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Enhancing Fault-Tolerance in MPLS Control Plane: LDP and BGP Mechanisms

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timon-velasquez
9 diapositives · 258 Views · Oct 26, 2014

This lecture delves into fault-tolerance architecture for MPLS, focusing on LDP and BGP mechanisms. It outlines three key approaches—Fault Tolerance for LDP, Checkpointing Procedures, and Graceful Restart. The discussion includes challenges with TCP sessions during control plane failures and introduces enhanced behaviors for LDP and BGP required to maintain forwarding states. Additionally, the lecture covers the Graceful Restart Capability for BGP that ensures preservation of MPLS forwarding state during restarts, underscoring its importance for network stability and reliability.

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  1. Lecture 15 MPLS Fault-Tolerance Architecture (For details, see class notes)

  2. LDP Fault-Tolerance Approaches • Three approaches have been proposed to minimize disruption of MPLS forwarding due to LDP restart: • Fault Tolerance for the LDP (RFC 3479) • Checkpointing Procedures for LDP (RFC 3479) • Graceful Restart Mechanism for LDP (RFC 3478)

  3. MPLS Control Plane (BGP/LDP) Restart - Problem Description • LDP and BGP use TCP as a reliable transport mechanism for its protocol messages. • The TCP session between two LDP/BGP peers may go down for several reasons such as control processor switchover due to HW/SW failures. • On detection of TCP session failure, existing LDP and BGP control plane components would disrupt their forwarding state. • To minimize disruption in MPLS forwarding plane due to MPLS control plane (LDP,BGP) restart, LDP and BGP have been enhanced.

  4. LDP Restart Behavior – before/after fault-tolerance enhancement 1 Control Plane Control Plane Control Plane 3 3 3 Data Plane Data Plane Data Plane 2 2 LSPs LSPs 1 Control Plane Control Plane Control Plane Data Plane Data Pane Data Plane 2 2 LSPs LSPs

  5. 0 0 7 7 15 15 23 31 FT Session Type Length Value (TLV) 1 0 FT Session TLV = (0x0503) Length (= 4) FT Flags Reserved FT Reconnect Timeout (in milliseconds) Recovery Time (in milliseconds) R S A C L Reserved L=1 means GR-LDP is selected FT Reconnect = 0 means LSR is not NSF capable FT Recovery Time = 0 means LSR was unable to preserve MPLS forwarding state across restart

  6. B LDP Graceful Restart Operation C A Active Standby LDP Session Setup LDP Session Setup LDP Address messages LDP Address messages LDP Label Mapping (FEC1, L1) LDP Label Mapping (FEC1, L2) LSP through A-B-C is ready Switchover Standby Active LDP Session re-established LDP Session re-established LDP Label Mapping (FEC1, L1) LDP Label Mapping (FEC1, L2) Normal operation Normal operation

  7. BGP/MPLS Graceful Restart • BGP is used as a control plane mechanism for IP and MPLS • BGP Graceful Restart mechanism allows a router to preserve its IP forwarding state across restart (draft-ietf-idr-restart-06.txt). • BGP MPLS graceful mechanism is an extension to the above for allowing an LSR to preserve its MPLS forwarding state across BGP restart (draft-ietf-mpls-bgp-mpls-restart-02.txt) • BGP MPLS Graceful Restart mechanism requires preservation of MPLS forwarding state across BGP restart. • To accomplish this: • a new Graceful Restart Capability is defined which is carried in BGP Open message • an BGP Update message with no reachable NLRI and empty withdrawn NLRI is specified as an End-of-RIB marker. • AFI/SAFI pair in the Graceful Restart Cap is used by an LSR for indicating its ability to preserve MPLS forwarding state across BGP restart

  8. Course Summary

  9. Where do we go from here? (For details, see class notes)