MPLS Traffic Engineering

What is Traffic Engineering? The ability to put traffic where you want it Adapt in the face of topology changes Adhere to administrator-defined policies Copyright © 1998, Juniper Networks, Inc.

Motivation for traffic engineering IGP metrics tend to attract or repel all traffic Insufficient granularity Little predictability Results are unused capacity and congestion Copyright © 1998, Juniper Networks, Inc.

Traffic patterns Copyright © 1998, Juniper Networks, Inc.

Constraint Based Routing Use the IGP to distribute more information about the network Compute paths based on IGP information, policy information Use RSVP to set up MPLS LSPs Use MPLS as a forwarding mechanism Copyright © 1998, Juniper Networks, Inc.

IGP information Per link Flooded through IGP area Link bandwidth Reservation multiplier Per-priority reserved bandwidth IPv4 interface address Resource class Flooded through IGP area Copyright © 1998, Juniper Networks, Inc.

IGP modifications OSPF opaque LSA IS-IS new TLV, plus subTLVs implemented not yet documented IS-IS new TLV, plus subTLVs (almost) interoperable Copyright © 1998, Juniper Networks, Inc.

Constrained Shortest Path First Compute shortest path with sufficient capacity minimal IGP path metric matching resource classes matching other policies Result: complete path Copyright © 1998, Juniper Networks, Inc.

CSPF details Similar to a normal SPF, except during link examination: reject links without capacity reject links that don’t match color constraints (include or exclude) reject links that don’t match configured policy (e.g., a loose source route) Copyright © 1998, Juniper Networks, Inc.

RSVP establishes LSPs Propagate label setup along path Hop by hop propagation RSVP provides liveness, enforces priorities Extensions Negotiate label vales Allow LSPs to move gracefully Specify the path Record the path Copyright © 1998, Juniper Networks, Inc.

Why RSVP? Existing protocol machinery, doing almost exactly what’s necessary Change scope from a flow to an LSP Small number of modifications No need to inject prefixes into signaling Already carries nice encoding of traffic description Copyright © 1998, Juniper Networks, Inc.

MPLS forwarding Forwarding structure is now established At entry points, map traffic for exit points into LSP to exit router Automatically tied into BGP Result: most traffic can easily be engineered Copyright © 1998, Juniper Networks, Inc.