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Explicitly Routed Tunnels using MPLS Label Stack draft-gredler-spring-mpls-02

Explicitly Routed Tunnels using MPLS Label Stack draft-gredler-spring-mpls-02. Hannes Gredler hannes@juniper.net Yakov Rekhter yakov@juniper.net Luay Jalil luay.jalil@verizon.com Sriganesh Kini sriganesh.kini@ericsson.com. Rationale for SPRING.

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Explicitly Routed Tunnels using MPLS Label Stack draft-gredler-spring-mpls-02

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  1. Explicitly Routed Tunnels using MPLS Label Stackdraft-gredler-spring-mpls-02 Hannes Gredler hannes@juniper.net YakovRekhteryakov@juniper.net LuayJalilluay.jalil@verizon.com SriganeshKinisriganesh.kini@ericsson.com

  2. Rationale for SPRING • Do we neednew architectural documents for SPRING ? • Can Label stacking for achieving explicit routing be described using existing MPLS architecture (RFC3031) documents ? • Lets have a look at RFC3031 !

  3. Explicitly Routed Tunnels with MPLS • Explicitly Routed Tunnels • “If a Tunneled Packet travels from Ru to Rd over a path other than the Hop-by-hop path, we say that it is in an "Explicitly Routed Tunnel“(section 3.27.2 of RFC3031) • Explicitly routed tunnels realized by explicitly routed LSPs established via either RSVP-TE or CR-LDP require intermediate nodes of these tunnels to maintain per tunnel (per path) state • Is it possible to establish explicitly routed tunnels without requiring intermediate nodes of these tunnels to maintain per tunnel (per path) state ?

  4. Stacked LSPs for Explicitly Routed Tunnels (1) • YES ! • Insteadof an explicitly routed LSP, one can use stack of LSPs to realize explicitly routed tunnels • Such stack of LSPs provides the functionality to forward a packet through a sequence of LSP egress of the LSPs on the stack • the sequence of LSP egress represents the explicit route • Stack of LSPs in the control plane correspondsto the stack of labels in the data plane

  5. Constructing Label Stack at the Ingress • To construct label stack for an explicitly routed tunnel the ingress of that tunnel has to obtain label binding from the first intermediate nodes of each LSPs in the stack • First intermediate nodes of all LSPs in the stack, except for the topmost LSP, are remote label distribution peers of the ingress • Obtaining label bindings from remote label distribution peers could be done by extending link-state protocols (ISIS/OSPF) to provide label distribution • In certain scenarios Targeted LDP (T-LDP) couldbe used to obtain label bindings from remote label distribution peers

  6. Example

  7. “Rosetta Stone” of Segment Routing with MPLS • Segment = MPLS label advertised by the first intermediate point of an LSP • Segment list = MPLS label stack • Advertising segments in OSPF/ISIS = extending OSPF/ISIS to provide label distribution functionality

  8. Summary • For SPRING there is no need for further architectural documents to define MPLS label stacking • MPLS Label stacking for achieving explicit routing can perfectly be described using existing MPLS architecture (RFC3031) documents

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