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

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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

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Hierarchical Labels in LDP

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

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Sriganesh Kini | IETF80 Prague | March 27 - April 1, 2011 | Page 2 (11)

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)

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Alternatives considered

› Scale IGP › Use another protocol to distribute FECs (e.g. BGP) › Targeted LDP

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Sriganesh Kini | IETF80 Prague | March 27 - April 1, 2011 | Page 4 (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
r 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

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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

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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

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New/Changed TLVs

› Hierarchical Label TLV › Metric TLV › More Label TLV › Capability Parameter TLV

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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

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Example

› Pre-failure packet flow (with PHP)

A C B

FEC-1 FEC-1 FEC-n IP hdr FEC-1 Data

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Example (contd)

› On failure when A updates FTN/ILM entry for egress B › Traffic to FEC-1 recovers