MultiProtocolLabelSwitching(anintroduction) KarstKoymans ... · MPLS MultiProtocolLabelSwitching(anintroduction) KarstKoymans CosminDumitru Informatics Institute University of Amsterdam

MPLS

Multi Protocol Label Switching (an introduction)

Karst Koymans

Cosmin Dumitru

Informatics Institute

University of Amsterdam

(version 1.4, 2013/03/14 15:51:41)

Thursday, March 14, 2013

Karst Koymans Cosmin Dumitru (UvA) MPLS Thursday, March 14, 2013 1 / 26

1 Faster IP forwarding

ATM and MPLS

2 MPLS Operation

Labels, paths and switching

MPLS Control and Label Management

3 MPLS Applications

MPLS VPN techniques


Faster IP forwarding

Outline

1 Faster IP forwardingATM and MPLS

2 MPLS OperationLabels, paths and switchingMPLS Control and Label Management

3 MPLS ApplicationsMPLS VPN techniques


Faster IP forwarding

IP Forwarding

Forwarding IP packets

Normally done by destination IP address

Routing protocols are used to distribute layer 3 information

Decisions are made hop-by-hop independently

Connectionless operation

Routing protocol should offer consistency

Shortcomings

Routing tables may become very large

Search time is ≈ O(logN) for table of size N

Limited traffic engineering options

Layer 2 and layer 3 information is unrelated


Faster IP forwarding ATM and MPLS

Outline






ATM (Asynchronous Transfer Mode)

Uses small fixed size cells to transport dataEach cell contains 53 bytes

A fixed size header of 5 bytesA fixed size payload of 48 bytes

Often data needs to be fragmented

Uses VCs (Virtual Circuits) between endpointsSwitching based on labels

An 8-bit (UNI) or 12-bit (NNI) Virtual Path Identifier (VPI)An 16-bit Virtual Channel Identifier (VCI)

Switching lookup is now O(1)Promises QoS, for instance low jitter

Higher level protocols use the ATM Adaptation Layer (AAL)



MPLS (Multi Protocol Label Switching)

Defined in RFC 3031

Combine the best of both worlds

Packet forwarding

Circuit switching

Route at the edges, switch at the core

Multi Protocol

Agnostic to the protocol used at layer 2

Label Switching

Uses labels instead of IP addresses

Routing at the speed of switching

Hybrid, “layer 2.5”, shim protocolKarst Koymans Cosmin Dumitru (UvA) MPLS Thursday, March 14, 2013 7 / 26

MPLS Operation

Outline





MPLS Operation

MPLS Network

MPLS Network


MPLS Operation Labels, paths and switching

Outline






MPLS Label (RFC 3032)

0 19 20 22 23 24 31

Label Exp S TTL

MPLS packet label fields

Label Per router local semantics

Exp(erimental)a Class of Service

S(tack) Bottom of stack indication

T(ime) T(o) L(ive) Incoming IP TTL

aRenamed to TC (Traffic Class) by RFC 5462



LER (Label Edge Router)

LSR (Label Switching Router)

Label Edge Router

Positioned at the edge of the MPLS network

Adds or removes labels for incoming and outgoing traffic

Also called Edge Label Switch Router (eLSR)

Label Switch Router

Positioned in the core of the MPLS network

Swaps labels and forwards packets

Does not need to know about IP forwarding



FEC (Forwarding Equivalence Class) and

LSP (Label Switched Path)

Forwarding Equivalence Class

Packets which are forwarded in the same manner

Each label on a link determines a unique FEC

Every FEC is associated with a certain LSP

Label Switched Path

Sequence of intermediate routers on same stack depth

on the path from ingress to egress router

Hop-by-hop routing

Explicit routing



LIB (Label Information Base)

Mapping between previous hop (incoming port, label) and FEC

Mapping between FEC and next hop (outgoing port, label)

Each router has its own LIB

Details are implementation dependent

Generates an LFIB (Label Forwarding Information Base)

Input Port Incoming Port Label Output Port Outgoing Port Label

1 green 3 blue

2 red 1 orange



MPLS Operation (continued)

MPLS Network

1

3

2

4 5

6

0 Receive IP packet at edge router

1 Classify into FEC green

2 Push (label green)

3 Swap (label green, label red)

4 Swap (label red, label blue)

5 Pop (label blue)

6 Forward IP packet to destination


MPLS Operation MPLS Control and Label Management

Outline






MPLS Separation of Control and Data

Control Plane

Exchange layer 3 and label information

Several label distribution protocols (LDP, CR-LDP, RSVP-TE)

Also piggybacked on routing protocols (OSPF-TE, ISIS-TE, MP-BGP)

Data Plane

Switch (forward) packets based on labels

Push (ingress)

Swap (intermediate)

Swap and push (start LSP tunnel)

Pop and swap (end LSP tunnel)

Pop (egress)



LDP (Label Distribution Protocol)

UDP discovery and TCP session with peers

Adjacent LSRs inform each other of the label bindings

Downstream LSR determines the label

On demand or unsolicited

An IGP protocol is configured on all LSRs

New IGP routes lead to new label bindings

Labels can be withdrawn when IGP routes are no longer valid

Hard-state

Expected to work until explicitly torn down



RSVP-TE

(Resource Reservation Protocol – Traffic Engineering)

Extension of RSVP

Unreliable delivery (protocol 46; sometimes UDP)

Soft-state

Information needs to be periodically refreshed

An LSP is created by propagating an RSVP message to the endpoint

Paths are terminated if not refreshed on time


MPLS Applications

Outline





MPLS Applications

Applications (1)

TE (Traffic Engineering)

Traffic steering across network in order to fully utilize resources

With the help of RSVP-TE and OSPF-TE or IS-IS-TE

Full network view (OSPF, IS-IS) and extra information about link state

RSPV-TE creates LSPs on demand

QoS (Quality of Service)

Different types of service across the network

Enforcing drop probability, bandwidth and delay (queueing)

CoS bits or FEC (destination + class of service)


MPLS Applications

Applications (2)

VPN (Virtual Private Network)

Private connections over shared networks

Layer 2 or layer 3 based

Business can choose the needed type of service

Stacked labels: egress router and VPN identity

LDP (layer 2) or BGP (layer 3) is used to transport label information


MPLS Applications MPLS VPN techniques

Outline






Layer 2 VPN (1)

AToM (Any Transport over MPLS)

Transports layer 2 frames over an MPLS Network

ATM, Frame-Relay, PPP, Ethernet

Point-to-point service

From ingress router/interface to egress router/interface

Identified by using an inner label



Layer 2 VPN (2)

VPLS (Virtual Private LAN Service)

Transports layer 2 frames over an MPLS Network

Works multipoint-to-multipoint

The IP/MPLS core operates as a big virtual switch

Outer label used for normal MPLS forwarding

Inner label used for VPLS instances



Layer 3 VPN

Uses the MP-BGP (Multi Protocol BGP) extension of BGP

Introduces the VPN-IPv4 address family

Extends the 32-bit IPv4 address with a 64-bit RD (route distinguisher)

A BGP route for VPN-IPv4 includes an MPLS label

Each VPN has its own VRF (VPN Routing and Forwarding) instance

Keeping separate routing tables for the VPNs

Also separate from the global routing table

MPLS forwarding uses stacked labels

Outer label for LSP forwarding

Inner label to differentiate between different VPNsKarst Koymans Cosmin Dumitru (UvA) MPLS Thursday, March 14, 2013 26 / 26

Documents

MultiProtocolLabelSwitching(anintroduction) KarstKoymans ... · MPLS MultiProtocolLabelSwitching(anintroduction) KarstKoymans CosminDumitru Informatics Institute University of Amsterdam