RFC 3031: Multiprotocol Label Switching Architecture Chapter 3.27 – /07/14 (Thu) Shinichi Ishida 2005/07/14 (Thu) Shinichi Ishida

3.27. Tunnels and Hierarchy Ru takes explicit action to deliver packet to Rd, even though Ru&Rd is not consecutive and Rd is not the ultimate destination => encapsulate the packet inside a network layer Hop-by-Hop Routed Tunnel Tunneled Packet follows the Hop-by-Hop path Explicitly Routed Tunnel Tunneled Packet travels over a path other than the Hop-by-Hop path Ru takes explicit action to deliver packet to Rd, even though Ru&Rd is not consecutive and Rd is not the ultimate destination => encapsulate the packet inside a network layer Hop-by-Hop Routed Tunnel Tunneled Packet follows the Hop-by-Hop path Explicitly Routed Tunnel Tunneled Packet travels over a path other than the Hop-by-Hop path

LSP Tunnels implemeting a tunnel as a LSP use label switching rather than network layer encapsulation the set of packets through the LSP tunnel constitutes a FEC, each LSR in the tunnel must assign a label to that FEC. implemeting a tunnel as a LSP use label switching rather than network layer encapsulation the set of packets through the LSP tunnel constitutes a FEC, each LSR in the tunnel must assign a label to that FEC.

Hierarchy: LSP Tunnels within LSPs R1R2R3R4 R21R22R23 IP L L L L

(1/3) Label Distribition Peering and Hierarchy when two LSRs are IGP neighbors > local label distibution peers not IGP neighbors > remote … when two LSRs are IGP neighbors > local label distibution peers not IGP neighbors > remote … R2R3 R21 IGP neighbors R1

(2/3) Label Distribition Peering and Hierarchy  Explicit Peering distribute labels by sending messages which are addressed to the peer useful when the number of remote peer is small the number of higher level label bindings is large the remote peers are in distinct routing areas  Explicit Peering distribute labels by sending messages which are addressed to the peer useful when the number of remote peer is small the number of higher level label bindings is large the remote peers are in distinct routing areas

(3/3) Label Distribition Peering and Hierarchy  Implicit Peering - encode a higher level label as an attribute of a lower label - distribute the lower leve label to local peers - local peers propagate the information to their local peers - continue till the information reaches the remote peer useful when the number of remote peers is large (not require n-square peering mesh)  Implicit Peering - encode a higher level label as an attribute of a lower label - distribute the lower leve label to local peers - local peers propagate the information to their local peers - continue till the information reaches the remote peer useful when the number of remote peers is large (not require n-square peering mesh)

3.28. Label Distribution Protocol Transport label distribution protocol : establish and maintain the label binding Needs: reliability, in sequence, flow control use TCP as the underlying transport [MPLS-LDP] [MPLS-BGP] label distribution protocol : establish and maintain the label binding Needs: reliability, in sequence, flow control use TCP as the underlying transport [MPLS-LDP] [MPLS-BGP]

3.29. Why More than one Label Distribution Protocol ? ‘ which ’ label distribution protocol to use in ‘ which ’ circumstances ? # this architecture does NOT establish hard and fast rules for choosing point out some of the considerations in the following sections ( – ) ‘ which ’ label distribution protocol to use in ‘ which ’ circumstances ? # this architecture does NOT establish hard and fast rules for choosing point out some of the considerations in the following sections ( – )

BGP and LDP desirable to bind labels to FECs idetified with routes to address prefixes If there is a standard, widely deployed routing algorithm -> label distribution is best achived by piggybacking on that ex) BGP a number of advantages RR:significant scalability desirable to bind labels to FECs idetified with routes to address prefixes If there is a standard, widely deployed routing algorithm -> label distribution is best achived by piggybacking on that ex) BGP a number of advantages RR:significant scalability

Labels for RSVP Flowspecs When RSVP is used for particular flows desirable to label the packets in those flows → RSVP filterspec: not need to be applied at each hop most efficient method of distributing labels = having RSVP distribute the labels as part of its path/reservation setup process ? When RSVP is used for particular flows desirable to label the packets in those flows → RSVP filterspec: not need to be applied at each hop most efficient method of distributing labels = having RSVP distribute the labels as part of its path/reservation setup process ?

Labels for Explicitly Routed LSPs It is desirable for traffic engineering - to set up an explicitly routed path - to apply resource reservations along that path two approaches It is desirable for traffic engineering - to set up an explicitly routed path - to apply resource reservations along that path two approaches start with existing protocolextend to supportexample 1resource reservationsexplicit routing & label distribution MPLS-RSVP- TUNNELS 2label distributionexplicit routing & resource reservations MPLS-CR- LDP