Hierarchical Labels in LDP draft-kini-mpls-ldp-hierarchy-00 Author: - PowerPoint PPT Presentation

Hierarchical Labels in LDP draft-kini-mpls-ldp-hierarchy-00 Author: Sriganesh Kini IETF 80 Prague, March 27 – April 1, 2011

Problem statement › Typical LDP deployments advertise a unique label per FEC › When nexthop changes (e.g. due to failure), ILM and FTN entries need to be updated. › Under scaled scenarios this leads to slower convergence – Detection time (Nexthop change) – Download time (Control to data plane) Sriganesh Kini | IETF80 Prague | March 27 - April 1, 2011 | Page 2 (11)

Alternatives considered › Scale IGP › Use another protocol to distribute FECs (e.g. BGP) › Targeted LDP Sriganesh Kini | IETF80 Prague | March 27 - April 1, 2011 | Page 3 (11)

Solution › Changes restricted to LDP › Include “Egress LSR Address” for a FEC in LDP messages. The label is referred to as a hierarchical label or H-Label . › Transport the label mapping with H-Label to all LSRs in the area. (Note: Label mapping to Egress LSR address is unchanged) › Transport the metric info for a FEC in LDP. › Install LSP to the shortest-path to the FEC Sriganesh Kini | IETF80 Prague | March 27 - April 1, 2011 | Page 4 (11)

Solution (contd) › Use label hierarchy by stacking a label to the Egress above the label of the FEC › Under failure, downloading the changed nexthop to the egress results in traffic being restored Sriganesh Kini | IETF80 Prague | March 27 - April 1, 2011 | Page 5 (11)

Solution characteristics › Works with both link-state and non link-state IGPs › Enables IGP to carry minimal info – Added side effect of IGP speed up due to carrying less state › With PHP no extra labels required on data path Sriganesh Kini | IETF80 Prague | March 27 - April 1, 2011 | Page 6 (11)

New/Changed TLVs › Hierarchical Label TLV › Metric TLV › More Label TLV › Capability Parameter TLV Sriganesh Kini | IETF80 Prague | March 27 - April 1, 2011 | Page 7 (11)

Messages and procedures › Supports all current label distribution/control and retention modes – Label Mappings received from the neighbor that has the nexthop to the Egress is chosen for advertisement to neighbors › Metric comparison procedure – Allows preference between different metric types Sriganesh Kini | IETF80 Prague | March 27 - April 1, 2011 | Page 8 (11)

Example IP hdr Data FEC-1 FEC-1 FEC-1 A B FEC- n C › Pre-failure packet flow (with PHP) Sriganesh Kini | IETF80 Prague | March 27 - April 1, 2011 | Page 9 (11)

Example (contd) FEC-1 FEC-1 A B FEC- n Lbl IP hdr IP hdr Data Data FEC-1 FEC-1 B C › On failure when A updates FTN/ILM entry for egress B › Traffic to FEC-1 recovers Sriganesh Kini | IETF80 Prague | March 27 - April 1, 2011 | Page 10 (11)

Comments/Questions Sriganesh Kini | IETF80 Prague | March 27 - April 1, 2011 | Page 11 (11)