mpls - os3 · faster ip forwarding atm and mpls mpls (multi protocol label switching) deﬁned in...

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MPLSMulti Protocol Label Switching (an introduction)

Karst Koymans

Informatics InstituteUniversity of Amsterdam

(version 4.3, 2015/03/09 13:07:57)

Thursday, March 12, 2015

Karst Koymans (UvA) MPLS Thursday, March 12, 2015 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 packetsNormally done by destination IP addressRouting protocols are used to distribute layer 3 informationDecisions are made hop-by-hop independently

Connectionless operationRouting protocol should offer consistency

ShortcomingsRouting tables may become very large

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

Limited traffic engineering optionsLayer 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)Karst Koymans (UvA) MPLS Thursday, March 12, 2015 6 / 26


MPLS (Multi Protocol Label Switching)

Defined in RFC 3031Combine the best of both worlds

Packet forwardingCircuit switchingRoute at the edges, switch at the core

Multi ProtocolAgnostic to underlying protocols used at layer 2 or 3

Label SwitchingUses labels instead of IP addressesRouting at the speed of switching

Hybrid, “layer 2.5”, shim protocolKarst Koymans (UvA) MPLS Thursday, March 12, 2015 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 RouterPositioned at the edge of the MPLS networkAdds or removes labels for incoming and outgoing trafficAlso called Edge Label Switch Router (eLSR)

Label Switch RouterPositioned in the core of the MPLS networkSwaps labels and forwards packetsDoes not need to know about IP forwarding



FEC (Forwarding Equivalence Class) and

LSP (Label Switched Path)

Forwarding Equivalence ClassPackets which are forwarded in the same mannerEach label on a link determines a unique FECEvery FEC is associated with a certain LSP

Label Switched PathSequence of intermediate routers on same stack depthon the path from ingress to egress router

Hop-by-hop routingExplicit 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 LIBDetails 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 PlaneExchange 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 PlaneSwitch (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 bindingsDownstream LSR determines the labelOn 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-stateExpected to work until explicitly torn down



RSVP-TE

(Resource Reservation Protocol – Traffic Engineering)

Extension of RSVPUnreliable 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 resourcesWith the help of RSVP-TE and OSPF-TE or IS-IS-TEFull network view (OSPF, IS-IS) and extra information about link stateRSPV-TE creates LSPs on demand

QoS (Quality of Service)Different types of service across the networkEnforcing 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 networksLayer 2 or layer 3 basedBusiness can choose the needed type of serviceStacked labels: egress router and VPN identityLDP (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/interfaceIdentified by using an inner label



Layer 2 VPN (2)

VPLS (Virtual Private LAN Service)Transports layer 2 frames over an MPLS NetworkWorks multipoint-to-multipointThe IP/MPLS core operates as a big virtual switch

Outer label used for normal MPLS forwardingInner 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 labelEach VPN has its own VRF (VPN Routing and Forwarding) instance

Keeping separate routing tables for the VPNsAlso separate from the global routing table

MPLS forwarding uses stacked labelsOuter label for LSP forwardingInner label to differentiate between different VPNs


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