1. CS 672 1 Summer 2003 Lecture 15 MPLS Fault-Tolerance Architecture ( For details, see class notes)

2. CS 672 2 Summer 2003 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. CS 672 3 Summer 2003 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. CS 672 4 Summer 2003 LDP Restart Behavior – before/after fault- tolerance enhancement LSPs Control Plane Data Plane Control Plane Data Plane Control Plane Data Plane 333 1 22 Control Plane Data Plane Control Plane Data Pane Control Plane Data Plane 1 22 LSPs

5. CS 672 5 Summer 2003 FT Session Type Length Value (TLV) FT Session TLV = (0x0503) 07152331 10 Length (= 4) FT FlagsReserved FT Reconnect Timeout (in milliseconds) Recovery Time (in milliseconds) Reserved 0715 RLCAS 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. CS 672 6 Summer 2003 LDP Graceful Restart Operation A ActiveStandby LDP Session Setup LDP Address messages LDP Label Mapping (FEC1, L1) LDP Label Mapping (FEC1, L2) LSP through A-B-C is ready Switchover ActiveStandby LDP Session re-established LDP Label Mapping (FEC1, L1) LDP Label Mapping (FEC1, L2) Normal operation B C

7. CS 672 7 Summer 2003 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. CS 672 8 Summer 2003 Course Summary

9. CS 672 9 Summer 2003 Where do we go from here? ( For details, see class notes)