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MPLS Architectural Principles. George Swallow ( swallow@cisco.com). MPLS Guiding Principles. Co-existence with IP IP based Control Planes Reuse of IP protocols Extendable protocols Pragmatism. MPLS Architectural Principles. Separation of Control Plane and Data Plane

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MPLS Architectural Principles


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mpls architectural principles
MPLSArchitecturalPrinciples

George Swallow

(swallow@cisco.com)

mpls guiding principles
MPLS Guiding Principles
  • Co-existence with IP
  • IP based Control Planes
  • Reuse of IP protocols
  • Extendable protocols
  • Pragmatism
mpls architectural principles1
MPLS Architectural Principles
  • Separation of Control Plane and Data Plane
  • Label semantics (except reserved) belong to application
    • Forwarding Equivalence Class
  • Compact Header
  • Multiple, Independent Control Planes
  • Label Stack
some contextual background
Some contextual background
  • Ratio of processor speeds to data-link speed much lower
  • Cost of a bit orders of magnitude higher
  • Getting links was very slow
  • IP community did not like ATM and particularly the “cell tax”
dataplane requirements
Dataplane Requirements
  • Very fast (i.e few gates and/or few cycles per packet)
  • Very widerange of equipment
  • Simple Data Plane
  • StableData Plane
    • Needs to work for lifetime of equipment (>10 yrs)
      • Including boxes for which
      • New linecards cannot be cost justified
      • Software has become “functionally stable”
mpls components
MPLS Components

BGP RFC3107

  • Control components
      • Applications directly define and manipulate label bindings
      • Essentially they use labels to program data plane
  • Forwarding component
    • Simple label-swapping paradigm

LDP

SDN

L2VPN

mLDP

L3VPN

EVPN

MPLS-TP

Pseudo-

wires

RSVP-TE

Efficient label processing

simple forwarding plane
Simple Forwarding Plane

Label Stack Entry

  • Label determines simple forwarding operations
    • Push, Pop, Swap, Outgoing interface(s)
  • Class of Service + Label defines queuing, drop priority

0 1 2 3

0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

| Label | COS |S| TTL |

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

COS = Class of Service S = Stack Bit TTL = Time to Live

label semantics
Label Semantics
  • Defined by the application
  • Need only be known by LSRs that Push/Swap/Pop that label
  • Full semantics need only be known to the consumer of the label
  • Forwarding Equivalence Class
    • Simple powerful concept
    • Single label assigned to a set of packets that are to be treated identically
      • Note that CoS bits are not part of this definition
label space
Label Space
  • One Million Labels
  • 16 Reserved Labels

Intentionally a limited number

New values impact dataplane

  • Label Spaces per
    • LSR
    • Interface
context labels
Context Labels
  • One label can define a new label space
  • Powerful means of expanding the available labels
  • If you need more labels, this is the proper way to do it!
label stack
Label Stack
  • Arbitrary number of labels
  • Multiple control planes act on packets
  • Control planes are totally independent
  • Control plane at one level can be replaced
    • No impact on levels above or below

Unicast

Routing

Traffic

Engineering

VPN

VPN

Traffic Engineering

Unicast Routing

Virtual Private Network

Virtual Private Network

The single most important element in MPLS’ success

ideas proposed over and over
Ideas proposed over and over
  • Global Labels
  • Source Labels
  • Special encodings of labels
    • Special meanings to label bits
  • Special semantics for double labels
    • PoPtop label; processnext label; push PoP’ed label back on
    • 8 byte label stack entry
    • Special uses for CoSand / or TTL bits
  • Multiple EOS bits set in the label stack
other rejected abandoned ideas
Other rejected / abandoned ideas
  • Encoding labels into VLAN-IDs
  • Encoding labels into the IPv6 flow label
  • Label Stack Header
  • Labels in PIM
  • I’m sure I’ve missed some