• Multiprotocol Label Switching
  • RFC3031
  • Multiprotocol
    • Can transport different payloads
  • Layer 2 Payloads
    • Ethernet, Frame Relay, ATM, PPP, HDLC, etc.
  • Layer 3
    • IPv4, IPv6, etc.
  • Extensible for new future payloads
  • Label Switching
    • Switches traffic between interfaces based on locally significant label values.
  • Similar to legacy virtual circuit switching
    • Frame Relay input/output DLCI
    • ATM input/output VPI/VCI
  • Why?
    • Transparent tunneling over SP network
    • BGP Free core
      • Saves routing table space on Provider routers
    • Offer L2/L3 VPN service to customers.
      • No need for overlay VPN model
    • Traffic Engineering
      • Distribute load over underutilized links
      • Give Bandwidth guarantees
      • Route based on service type
      • Detect and repair failures quickly
        • Fast Reroute (FRR)
  • Label format
    • 4 byte header used to “switch” packets
      • 20 bit label – locally significant
      • 3 bit EXP – Class of Service
      • S bit – Defines last label in label stack
      • 8 bit TTL – TTL
  • Labels
    • MPLS labels are bound to FECs
      • Forwarding equivalency class
      • IPv4 or IPv6 for CCIE purposes.
        • Binding between label and IP prefix.
    • Router uses MPLS LFIB instead of IP routing table to switch traffic.
    • Switching Logic
      • If traffic comes in if1 with label X, send it out if2 with label Y
  • MPLS Device Roles
    • Consists of three types of devices
      • Customer Edge (CE)
      • Provider Edge (PE)
      • Provider (P)
  • CE
    • Last hop device in customer’s network.
      • Connects to provider’s network.
    • Can be layer 2 or 3.
    • Typically not aware any MPLS is running.
  • PE
    • Also called Label Edge Router (LER)
    • Last hop device in provider’s network.
      • Connects to CE and provider core devices.
    • Performs both IP routing and MPLS lookups.
    • Traffic from customer to core
      • Receives unlabeled packets (e.g. IPv4/6)
      • Adds one or more MPLS labels
      • Forwards labeled packet to core
    • Traffic from core to customer
      • Receives MPLS labeled packets.
      • Removes one or more MPLS labels.
      • Forwards packet to customer.
  • P
    • Also called Label Switch Router (LSR)
    • Core devices in provider’s network
    • Connects to PEs and other P routers
    • Switches traffic based ONLY on MPLS labels
  • Operations
    • PE and P routers perform three major functions:
      • Label push
        • Add a label to incoming
          • label imposition
      • Label Swap
        • Replace the label on an incoming packet
      • Label pop
        • Remove the labelfrom an outgoing packet
  • Label Distribution
    • Advertised via LD protocol
    • Label Distribution Protocol (LDP)
      • Advertises labels for IGP learned routes.
      • RFC 5036
    • MP-BGP
      • Advertises labels for BGP learned routes.
      • RFC 3107
    • RSVP
      • Used for MPLS Traffic Engineering (MPLS TE)
      • RFC 3209

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