Advanced Topics in Networking:MPLS and GMPLS

Hang LiuThomson Inc., Corporate Research Lab

Princeton, NJ

Note: Thank Dr. Debanjan Saha for the teaching materials on MPLS

MPLS: Multi-protocol Label Switching

3

Topics

Introduction History and motivation MPLS mechanisms

MPLS protocols RSVP-TE/CR-LDP

MPLS applications VPNSs, traffic engineering, restoration

Shirl Grant NLANR Engineering Services

4

WHY MPLS ?

Ultra fast forwarding Use switching instead of

routing IP Traffic Engineering

Constraint-based routing Virtual Private Networks

Controllable tunneling mechanism

Protection and restoration

5

IP Forwarding Table

47.1.*.*

47.2.*.*47.3.*.*

Dest Out

47.1 147.2 2

47.3 3

1

23

Dest Out

47.1 147.2 2

47.3 3

Dest Out

47.1 147.2 2

47.3 3

1

23

1

2

3

6

Hop-by-Hop IP Forwarding

47.1

47.247.3

IP 47.1.1.1

Dest Out

47.1 147.2 2

47.3 3

1

23

Dest Out

47.1 147.2 2

47.3 3

1

2

1

2

3

IP 47.1.1.1

IP 47.1.1.1IP 47.1.1.1

Dest Out

47.1 147.2 2

47.3 3

7

Routing Lookup

Longest prefix match is (was) expensive. Label matching is much less expensive.

10 Gbps 10 Gbps

20M packets/sec

Switchfabric

Control CPU

I/F I/F

9.*.*.* 14.1.2.1 29.1.*.* 67.1.2.2 49.2.*.* 71.1.2.3 69.1.1.* 113.1.2.1 89.2.1.* 113.1.2.1 89.1.1.1 71.1.2.3 69.1.1.2 14.1.2.1 29.2.1.1 71.1.2.3 6

Prefix Next Hop Interface

8

IntfIn

LabelIn

Dest IntfOut

3 0.40 47.1 1

IntfIn

LabelIn

Dest IntfOut

LabelOut

3 0.50 47.1 1 0.40

MPLS Labels

47.1

47.247.3

1

2

31

2

1

2

3

3IntfIn

Dest IntfOut

LabelOut

3 47.1 1 0.50 Mapping: 0.40

Request: 47.1

Mapping: 0.50

Request: 47.1

9

Label Switched Path

IntfIn

LabelIn

Dest IntfOut

3 0.40 47.1 1

IntfIn

LabelIn

Dest IntfOut

LabelOut

3 0.50 47.1 1 0.40

47.1

47.247.3

1

2

31

2

1

2

3

3IntfIn

Dest IntfOut

LabelOut

3 47.1 1 0.50

IP 47.1.1.1

IP 47.1.1.1

10

Forwarding Equivalence Classes

FEC = “A subset of packets that are all treated the same way by a router” The concept of FECs provides for a great deal of flexibility and scalability In conventional routing, a packet is assigned to a FEC at each hop (i.e. L3

look-up), in MPLS it is only done once at the network ingress

Packets are destined for different address prefixes, but can be mapped to common pathPackets are destined for different address prefixes, but can be mapped to common path

IP1

IP2

IP1

IP2

LSRLSRLER LER

LSP

IP1 #L1

IP2 #L1

IP1 #L2

IP2 #L2

IP1 #L3

IP2 #L3

11

MPLS Terminology

LDP: Label Distribution Protocol LSP: Label Switched Path FEC: Forwarding Equivalence Class LSR: Label Switching Router LER: Label Edge Router

12

Label Distribution Methods

LSR1 LSR2

Downstream Label Distribution

Label-FEC Binding

• LSR2 discovers a ‘next hop’ for a particular FEC

• LSR2 generates a label for the FEC and communicates the binding to LSR1

• LSR1 inserts the binding into its forwarding tables

• If LSR2 is the next hop for the FEC, LSR1 can use that label knowing that its meaning is understood

LSR1 LSR2

Downstream-on-Demand Label Distribution

Label-FEC Binding

• LSR1 recognizes LSR2 as its next-hop for an FEC

• A request is made to LSR2 for a binding between the FEC and a label

• If LSR2 recognizes the FEC and has a next hop for it, it creates a binding and replies to LSR1

• Both LSRs then have a common understanding

Request for Binding

Both methods are supported, even in the same network at the same time

13

Distribution Control

Independent LSP ControlIndependent LSP Control Ordered LSP ControlOrdered LSP Control

Next Hop(for FEC)

OutgoingLabel

IncomingLabel

• Each LSR makes independent decision on when to generate labels and communicate them to upstream peers

• Communicate label-FEC binding to peers once next-hop has been recognized

• LSP is formed as incoming and outgoing labels are spliced together

• Label-FEC binding is communicated to peers if: - LSR is the ‘egress’ LSR to particular FEC - label binding has been received from

upstream LSR

• LSP formation ‘flows’ from egress to ingress

DefinitionDefinition

ComparisonComparison • Labels can be exchanged with less delay• Does not depend on availability of egress node• Granularity may not be consistent across the nodes

at the start• May require separate loop detection/mitigation

method

• Requires more delay before packets can be forwarded along the LSP

• Depends on availability of egress node• Mechanism for consistent granularity and freedom

from loops• Used for explicit routing and multicast

Both methods are supported in the standard and can be fully interoperable

14

Label Retention Methods

Liberal Label Retention Conservative Label Retention

LSR1

LSR2

LSR3

LSR4

Label Bindingsfor LSR4

Valid Next Hop

LSR4’s LabelLSR3’s LabelLSR2’s Label

LSR1

LSR2

LSR3

LSR4

Label Bindingsfor LSR4

Valid Next Hop

LSR4’s LabelLSR3’s LabelLSR2’s Label

• LSR maintains bindings received from LSRs other than the valid next hop

• If the next-hop changes, it may begin using these bindings immediately

• May allow more rapid adaptation to routing changes

• Requires an LSR to maintain many more labels

• LSR only maintains bindings received from valid next hop

• If the next-hop changes, binding must be requested from new next hop

• Restricts adaptation to changes in routing

• Fewer labels must be maintained by LSR

Label Retention method trades off between label capacity and speed of adaptation to routing changes

15

Label Encapsulation

ATM FR Ethernet PPP

MPLS Encapsulation is specified over various media types. Top labels may use existing format, lower label(s) use a new “shim” label format.

VPI VCI DLCI “Shim Label”

L2

Label

“Shim Label” …….

IP | PAYLOAD

16

Label Format

Exp field used to identify the class of service Stack bit is used identify the last label in the

label stack TTL field is used as a time-to-live counter. Special

processing rules are used to mimic IP TTL semantics.

Label 20 bits

Exp 3 bits

Stack1 bit

TTL8 bits

17

Label Distribution Protocols

Label Distribution Protocol (LDP) Constraint-based Routing LDP (CR-

LDP) Extensions to RSVP Extensions to BGP

18

LDP:Label Distribution Protocol

Label distribution ensures that adjacent routers havea common view of FEC <-> label bindings

Routing Table:

Addr-prefix Next Hop47.0.0.0/8 LSR2

Routing Table:

Addr-prefix Next Hop47.0.0.0/8 LSR2

LSR1 LSR2 LSR3

IP Packet 47.80.55.3

Routing Table:

Addr-prefix Next Hop47.0.0.0/8 LSR3

Routing Table:

Addr-prefix Next Hop47.0.0.0/8 LSR3

For 47.0.0.0/8use label ‘17’

Label Information Base:

Label-In FEC Label-Out17 47.0.0.0/8 XX

Label Information Base:

Label-In FEC Label-Out17 47.0.0.0/8 XX

Label Information Base:

Label-In FEC Label-OutXX 47.0.0.0/8 17

Label Information Base:

Label-In FEC Label-OutXX 47.0.0.0/8 17

Step 1: LSR creates bindingbetween FEC and label value

Step 2: LSR communicatesbinding to adjacent LSR

Step 3: LSR inserts labelvalue into forwarding base

Common understanding of which FEC the label is referring to!

19

LDP: Basic Characteristics

Provides LSR discovery mechanisms to enable LSR peers to find each other and establish communication

Defines four classes of messages DISCOVERY: deals with finding neighboring LSRs ADJACENCY: deals with initialization, keep alive, and shutdown of

sessions LABEL ADVERTISEMENT: deals with label binding advertisements,

request, withdrawal, and release NOTIFICATION: deals with advisory information and signal error

information Runs over TCP for reliable delivery of messages, except

for discovery, which uses UDP and IP multicast Designed to be extensible, using messages specified as

TLVs (type, value, length) encoded objects.

20

LDP Messages

INITIALIZATION KEEPALIVE LABEL MAPPING LABEL WITHDRAWAL LABEL RELEASE LABEL REQUEST

21

IntfIn

LabelIn

Dest IntfOut

3 0.40 47.1 1

IntfIn

LabelIn

Dest IntfOut

LabelOut

3 0.50 47.1 1 0.40

47.1

47.247.3

1

2

31

2

1

2

3

3

IntfIn

Dest IntfOut

LabelOut

3 47.1.1 2 1.333 47.1 1 0.50

IP 47.1.1.1

IP 47.1.1.1

Explicitly Routed LSP

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ER LSP - Advantages

Operator has routing flexibility policy-based, QoS-based

Can use routes other than shortest path

Can compute routes based on constraints in exactly the same manner as ATM based on distributed topology database.(traffic engineering)

23

ER LSP - discord!

Two signaling options proposed in the standards: CR-LDP, RSVP extensions:

CR-LDP = LDP + Explicit Route RSVP ext = Traditional RSVP + Explicit

Route +Scalability Extensions Market will probably have to resolve it Survival of the fittest not such a bad

thing.

24

MPLS and QoS in IP Network

Integrated Services Differentiated Services

25

Integrated Services Internet

Applications specify traffic and service specs Tspec: traffic specs including peak rate, maximum

packet size, burst size, and mean rate Rspec: service spec, specifically service rate

Two classes of service defined Guaranteed service: satisfies hard guarantees on

bandwidth and delay Controlled load service: provides service similar to that

in “unloaded network” RSVP was extended to RSVP-TE support signaling

RSVP was further extend to add MPLS support

26

Differentiated Services Internet

IP packets carry 6-bit service code points (DSCP) Potentially support 64-different classes of services

Routers map DSCP to per-hop-behavior (PHB) PHBs can be standard or local Standard PHBs include

Default: No special treatment or best effort Expedited forwarding (EF): Low delay and loss Assured forwarding (AF): Multiple classes, each class with multiple

drop priorities LSRs don’t sort based on IP headers, hence DSCPs need to

be mapped to EXP field in MPLS shim header Exp field is only 3-bit wide – can support only 8 DSCPs/PHBs Labels can be used if more than 8 PHBs need to be supported Same approach can be used for link layers which do not use

Shim headers, e.g. ATM

27

Traffic Engineering with RSVP

Sender

Receiver

PATH {Tspec}

RESV{Rspec}

PATH {Tspec}

PATH {Tspec} PATH

{Tspec}

RESV{Rspec}

RESV{Rspec}

RESV{Rspec}

28

Label Distribution with RSVP-TE

PATH {Tspec}

RESV{Rspec}

{Label = 5}

RESV{Rspec}

{Label = 10}

Sender

PATH {Tspec}

RESV{Rspec}

PATH {Tspec}

PATH {Tspec} PATH

{Tspec}

RESV{Rspec}

29

MPLS Protection

End-to-end protection Fast node and link reroute

30

MPLS ProtectionEnd-to-end Path Protection

A

C

BD

E

F

Backup LSP

Primary LSP

Backup and primary LSPs should be route diverse

31

MPLS Protection: Fast Reroute

LSR A

LSR F

LSR E

LSR D

LSR C

LSR B

Detour to avoid AB

Detour to avoid BC

Detour to avoid CD

Detour to avoid DE

Detour to avoid link DE

Detour around node or link failures Example LSP shown traverses (A, B, C, D, E, F)

Each detour avoids Immediate downstream node & link towards it Except for last detour: only avoids link DE

32

Detour Merging

LSR A

LSR F

LSR E

LSR D

LSR C

LSR B

Detour to avoid AB

Detour to avoid BC

Merged detour to avoid AB and BC

Reduces state maintained Improves resource utilization

33

MPLS Protection Types

1+1: Backup LSP established in advance, resources dedicated, data simultaneously sent on both primary and backup

Switchover performed only by egress LSR Fastest, but most resource intensive

1:1 : Same as 1+1 with the difference that data is not sent on the backup

Requires failure notification to the ingress LSR to start transmitting on backup

Notification may be send to egress also Resources in the backup may be used by other traffic

Low priority traffic (e.g., plain IP traffic), shared by other backup paths

34

MPLS VPN: The Problem

10.1/16

10.1/16

10.2/16

10.2/16

10.3/16

10.3/16

Provider NetworkCustomer 1

Site 1

Customer 1Site 2

Customer 1Site 3

Customer 2Site 3

Customer 2Site 1

Customer 2Site 2

35

MPLS VPN: The Model

10.1/16

10.1/16

10.2/16

10.2/16

10.3/16

10.3/16

Customer 1Site 1

Customer 2Site 1

Customer 2Site 3

Customer 1Site 3

Customer 2Site 2

Customer 1Site 2

Customer 1Virtual Network

Customer 2Virtual Network

36

MPLS VPN: The Solution

10.1/16

10.1/16

10.2/16

10.2/16

10.3/16

10.3/16

Customer 1Site 1

Customer 1Site 2

Customer 1Site 3

Customer 2Site 3

Customer 2Site 1

Customer 2Site 2

VRF 1

VRF 1

VRF 1

VRF 2

VRF 2

VRF 2

MPLS LSP

MPLS LSP

GMPLS: Generalized MPLS & ASON: Automatically Switched

Optical Network

38

Outline

ASON Control Plane Standards UNI and NNI Protection and Restoration

39

Traditional Management Plane for Optical Transport Networks

A lot of manual operations Integration of different EMS and NMS is complex

multiple types of equipment from different vendors with different technologies

Automatic end-to-end provisioning is not easy planning, path computation, connection establishment

Class 5

IP

Optical Transport Network (OTN)

FR/ATM

IP

FR/ATM

Class 5

Other

Other

NMS

EMS 1 EMS 3

EMS 2

40

Distributed Control Plane

Distributed control plane offers automatic neighbor and topology discovery automatic end-to-end provisioning and connection modification scalability and interoperability unified traffic engineering and protection/restoration

In an environment where IP router networks are interconnected via a mesh optical network

OpticalDomain

OpticalDomain

OpticalDomain

Client Network(IP, ATM, SDH)

Optical TransportNetwork

ENNI

ENNIUNI UNI

signaling and routing over control channel

ENNI

INNI

NMS/EMS

SPC

SC

41

ASON Control Plane

Goals of ASON control plane Facilitate configuration of connections within an optical

transport network in a reliable, efficient, scalable, interoperable and automatic way

Switched connection (SC): requested by a user Soft permanent connection (SPC): initiated by the

management plane Good for applications required for dynamic circuits

(holding time ~ provisioning time) Allow reconfiguring or modifying connections for existing

calls Perform protection and restoration function

42

ASON Control Plane Components

Components of ASON control plane Call Controller Connection Controller Link Resource Manager Routing Controller Discovery Agent Termination and Adaptation Performer Etc.

43

Related Standard Bodies

ITU ASON Architecture and Components UNI and NNI interfaces

IETF Generalized GMPLS Protocols

Extends MPLS/IP protocols based on generalized interface requirements

signaling (RSVP-TE and CR-LDP with GMPLS extensions) routing (OSPF-TE and IS-IS with GMPLS extensions) link management and neighbor discovery (LMP)

OIF Focuses on application of IETF protocols in an overlay model Generates implementation agreements

UNI and NNI

44

GMPLS: Generalized MPLS

GMPLS Handles Nodes With Diverse Capabilities. Packet Switch Capable (PSC) Time Division Multiplexing Capable (TDM) Lambda Switch Capable (LSC) Fiber Switch Capable (FSC)

Each Node Is Treated As an MPLS Label-switching Router (LSR) Lightpaths/TDM Circuits Are Considered Similar to Label-Switched Paths

(LSPs) Selection of s and OXC ports are considered similar to selection of labels

FSC Cloud

LSCCloud

TDM Cloud

PSC Cloud

45

Overview of IETF GMPLS Protocols

GMPLS-based distributed control plane automatic service provisioning (signaling) dynamic network topology and resource availability

dissemination (routing) neighbor discovery and link management (link

management)

46

Control Channel

Bi-directional channel is required between two logically or physically adjacent nodes to exchange control messages

in-band with data (such as two IP routers, SONET overhead bytes)

out-of-band through a separate link or even separate network (such as an IP network)

de-couple data channel and control channel one control channel to one or multiple data channels

data channel 1 (and control channel)

data channel N

IP

control channel

Link Bundlecontrol channel

47

Connection Provisioning through GMPLS

Connection request received from a client or a management agent at ingress node

Ingress node computes the explicit route from ingress to egress node

take into account a set of constraints (bandwidth requirements, resource availability, protection/restoration and traffic engineering constraints)

Require routing protocol to disseminate network topology and link state information

Signaling the connection establishment along the path RSVP-TE or CR-LDP extension

Ingress Node (A)

Egress Node (B)

Request

48

Signaling Protocol

Establishes and deletes paths LSP setup: label request and resource reservation/allocation LSP deletion: label and resource release

GMPLS Signaling Extends MPLS label semantics to accommodate fiber, waveband,

lambda, TDM and packet-capable LSP establishment Extends RSVP-TE and CR-LDP for carrying the generalized label

objects over explicit path Supports bi-directional LSP setup Suggested Label

Upstream node suggests a label to downstream node for speeding up configuration

Label Set Limit the labels what downstream node can choose from

49

Routing Protocol

Disseminates network topology and link resource availability over control channel (CC)

Manages the link state database and routing tables make routing decision

Provides path computation algorithm with the routing information to obtain explicit route

Traffic engineering (TE) and GMPLS routing extensions Extends OSPF or IS-IS

Support multiple types of GMPLS TE links Carry new link attributes TE LSA database for explicit path computation

50

Link Bundling

Neighboring nodes (e.g. OXCs) connected by multiple parallel links For standard OSPF, each physical link between a pair of nodes forms a

routing adjacency not scale well

To improve routing scalability and reduce the amount of information handled by routing protocol, in GMPLS routing protocol

aggregates and abstracts the attributes of the links with similar characteristics between a pair of nodes

advertises as a single link bundle or Traffic Engineering (TE) link aggregation leads to information loss

Control channel and data link may be separated

Data Channel 1

Data Channel NLink Bundle

Component Link

51

Link Management Protocol (LMP)

Multiple fiber links between two adjacent nodes

(e.g. OXC, photonic switches)

Control channels may not use the same physical

medium and interfaces as the data links

Link Management Protocol (LMP) Provides the capability to manage control channel and

data links between neighboring nodes

52

LMP functionality

Control channel management establish and maintain LMP control channel

connectivity between adjacent nodes. Link property correlation (link bundling management)

synchronize TE link (link bundle) properties and verify the TE link properties

one CC per one or more link bundles Link connectivity verification

data link physical connectivity discovery mis-configuration and mis-wiring detection

Fault management localize and handle data link failure

Service discovery automatic discovery of services offered by the

network including signaling protocol type, link and data signal type, transparency level etc...

53

LMP Different Operation Modes

In-fiber and in-band control channel one CC per data component link e.g. using SONET/SDH overhead bytes control channel management and data link management can be

done together neighbor discovery mis-configuration and mis-wiring detection

Out-of-fiber control channel (Ethernet) or in-fiber dedicated channel,

one CC per multiple component links or multiple link bundles transparent devices that the data is not modified or examined in

normal operation.e.g. photonic switches test messages are used for data link neighbor discovery and

connectivity verification

54

LMP In-band Control

CID: Channel ID config: HelloInterval and helloDeadInterval hello: TxSeqNum and RcvSeqNumk

Node A Node BConfig (local CID, msg ID, local node ID, config)

ConfigAck (local CID, local node ID, remote CID, msg ID ACK, remote node ID)

ConfigNack (local CID, local node ID, remote CID, msg ID ACK, remote node ID, config)

ConfigAck (local CID, local node ID, remote CID, msg ID ACK, remote node ID)

Config (local CID, msg ID, local node ID, config)

Hello (local CID, hello)

Hello (local CID, hello)

Hello (local CID, hello)

Hello (local CID, hello)

ParameterNegotiation

Keep-alive

55

LMP Out-Of-Band Control

Most LMP messages are send out-of-band through the control channel In-band Test messages are sent for link verification and correlation TE link (link bundle) is disseminated over routing protocol Routing flooding adjacencies are maintained over control channel and

data forwarding adjacencies (FA) are maintained over component links

Data Channel 1

Data Channel N

Control Channel (CC)

Link Bundle

Test Messages

BeginVerify (control channel)

BeginVerifyAck (control channel)

Test (data link)

TestStatusAck (control channel)

TestStatusSuccess (control channel)

.Test other data component links.EndVerifyAck

56

Unified Control Plane

UNI - User-to-Network InterfaceI-NNI - Internal Network-to-Network InterfaceE-NNI - External Network-to-Network Interface

Optical Network

Optical subnet

Optical subnet

Optical subnet

UNI

UNI

E-NNIE-NNI

E-NNI

I-NNI

ATM Network IP Network

IP Network

ATM Network

ATM Network

ATM Network

ATM NetworkIP Network

ATM Network

ATM Network

57

User-to-Network Interface (UNI)

UNI supports establishment of connections between the client nodes over an OTN (overlay model)

Re-use IETF GMPLS protocols signaling: RSVP-TE, CR-LDP with UNI specific extensions neighbor and service discovery: LMP with UNI specific extensions

Transport network assigned address (TNA) an address assigned to a client by the transport service provider a globally unique address, can be IPv4, IPv6 or NSAP

UNI is used at the edge of the cloud Inside the cloud - LMP, GMPLS signaling and routing

OTNUNI UNI

LMP

Signaling

LMP

Signaling

LMP

Signaling/Routing

End-to-end path

Client Client

58

UNI Connection Setup Using GMPLS RSVP-TE

Source UNI-C

Path

Resv + MESSAGE_ID_ACK

Destination UNI-CIngress UNI-N Egress UNI-N

Path

Resv

ResvConf

ACK

ACK

ResvConf+ MESSAGE_ID_ACK

ACK

ACK

UNI Transport Connection EstablishedSource UNI-C may start transmitting

Destination UNI-C may start transmitting

59

Network-to-Network Interface

Inter-domain signaling: extends GMPLS signaling protocol, e.g. RSVP

Inter-domain routing

extends GMPLS IGP routing protocols: e.g. multi-area OSPF, IS-IS

extends inter-domain routing protocol (BGP) to exchange topology

information across domain boundaries

abstraction and summarization of intra-domain routing information

Neighbor discovery and link management: LMP

OTN1 OTN1 OTN1

Signaling SignalingSignaling

End-to-end path

UNI UNIENNI ENNIClient Client

Routing Routing

60

Path Protection and Restoration in OTN

Dedicated 1+1 Protection Primary and protection path diversified During normal operation mode, both paths are completely provisioned,

carry the optical data traffic and the egress elects the best copy of the two

Primary and protection path provisioning through GMPLS signaling protocols, e.g. RSVP

No delay but not efficient in terms of netwok resource utilization

A B C

D E

F G H

primary

primary

protection

protection

61

Shared Mesh Protection and Restoration

Shared mesh restoration path is pre-computed and pre-provisioned Resource is reserved on the links but no cross-connects are created along the

restoration path The complete establishment of the restoration path occurs only after the primary path

fails The common restoration resource reserved on a link may be shared by multiple

restoration paths to restore multiple primary paths In order to avoid contention during a single node failure, two restoration paths

may share the common reserved restoration resource only if their respective working paths are mutually node disjoint.

The bandwidth reserved for restoration on a link can be smaller than the total bandwidth required by all the working paths recovered by it

the resource reserved for restoration can also be used for low priority pre-emptible traffic in normal operating mode

Efficient but with a delay

A B C

D E

F G H

primary

primary

Shared restoration channel

62

GMPLS Control Plane Prototype

Routing Table

Manager

OSPF-TE

GMPLS Controller

Layer 3 (IP)

Layer 2 (Ethernet)

Switch Control

GUI/CLI Agent

Routing

Path Computation

LSA DB

RSVP-TE

Layer 2 (SONET)

Data Plane Control

GMPLS Interface Adapter

Signaling

IPCLink Management

Link Bundle TablePort Table Path Table

GMPLS Application

GMPLS Management

GUI/CLI

Optical SwitchGMPLS Database