MTNL MPLS Tutorial DrVishalSharma 2006-04-26

7/29/2019 MTNL MPLS Tutorial DrVishalSharma 2006-04-26

1/34

Multi-Protocol Label Switching:

Basics & Applications

Dr. Vishal SharmaEmail: [email protected]: http://www.metanoia-inc.com

Metanoia, Inc.Critical Systems Thinking

Copyright 2002-2005

All Rights Reserved


2/34


Copyright 2002-2005

All Rights Reserved MPLS Seminar, MTNL CETTM, Mumbai, 26th April 2005 2

The Start: Routing Process at a Router

Destination address (DA)based forwarding

Longest prefix matching

Routing Table

DA=my_add orDA= IP brdcst add.

?

RT entry =complete DA?

RT entry =Destn. n/w id?

Default entryexists?

No

No

No

No

Yes

Yes

Yes

Yes

Deliver datagram toprotocol module(TCP/UDP) specifiedin IP hdr.

Send pkt. to next-hop

router or to directlyconnected interface.

Send pkt. to next-hop router or todirectly connected

interface.

Send pkt. tonext-hop router.

Datagram undeliverable. (Use ICMP to inform source.)

Receive incoming pkt.

DA Next hoprouter

NetworkInterface

Host entry 198.168.7.3 X 2

Host entry 198.168.7.4 X 3

Host entry 198.168.7.1 198.168.7.5 1

Host entry 198.168.7.2 198.168.7.5 1

N/w entry 198.100.x.x 198.100.9.1 4

N/w entry 128.72.x.x 128.72.55.4 5

Default x.x.x.x 128.84.73.1 6


3/34


Copyright 2002-2005


How Routing Works Today

How do routers build their routing tables?

By exchanging information with each other using routing protocols

DA Next hoprouter

N/wInt.

Host entry 198.168.7.3 X 2

Host entry 198.168.7.4 X 3

Host entry 198.168.7.1 198.168.7.5 1

Host entry 198.168.7.2 198.168.7.5 1

N/w entry 198.100.x.x 198.100.9.1 4

N/w entry 128.72.x.x 128.72.55.4 5

Default x.x.x.x 128.84.73.1 6

Routing table (RT) at 198.168.7.6

Longest prefix matchgives next hop routeras 198.100.9.1 and

outgoing interface as

4.

198.100.9.75

198.100.9.75

198.100.9.75

198.100.9.75

198.100.9.75198.168.7.4

198.168.7.3

198.168.7.1

198.168.7.2

198.168.7.5

198.168.7.6

198.100.x.x

198.100.9.1

128.72.x.x

128.72.55.4

128.84.x.x

128.84.73.1

23

4

56

1

198.100.9.7

5

DA = 198.100.9.75

Packet generated


4/34


Copyright 2002-2005


How it Would be with Labels

How do routers learn the labels?

By interpreting routing information and through signaling

(as we will learn later)

DA = 198.100.9.75Packet generated

Exact matchinglabelswapping gives outgoing

label as and outgoing

interface as 4.

Incominglabel

Outgoinglabel

Address pref ix N/wInt.

X 2

198.100.x.x 4

128.72.x.x 5

Label Forwarding Table at 198.168.7.6

198.168.7.4

198.168.7.3

198.168.7.1

198.168.7.2

198.168.7.5

198.168.7.6

198.100.x.x

198.100.9.1

128.72.x.x

128.72.55.4

128.84.x.x

128.84.73.1

23

4

56

1

198.100.9.7

5

Attach label


5/34


Copyright 2002-2005


Shortest-Path Routing: Little Flexibility

Shortest path converges traffic on a few network links

Significant increase in congestion

Unbalanced resource utilization

DA Next hop

router

N/w

Int.

Host entry 198.168.7.4 X 3

Host entry 198.168.7.1 198.168.7.5 1

Host entry 198.168.7.2 198.168.7.5 1

N/w entry 198.101.x.x 198.168.7.4 3

N/w entry 198.100.x.x 198.100.9.1 4

N/w entry 128.72.x.x 128.72.55.4 5

Default x.x.x.x 128.84.73.1 6

Routing table (RT) at 198.168.7.6

198.168.7.4198.168.7.1

198.168.7.2

198.168.7.5

198.168.7.6

198.100.x.x

198.100.9.1

128.72.x.x

128.72.55.4

128.84.x.x

128.84.73.1

3

45

6

1

198.100.9.7

5

198.101.84.21

R1

R2

R3

R4


6/34


Copyright 2002-2005


Labels De-couple Routing andForwarding: Much more Flexibility

Labels enable:

Differentiation based on criteria other than shortest path

Permit policy routing

198.168.7.4198.168.7.1

198.168.7.2

198.168.7.5

198.168.7.6

198.100.x.x

198.100.9.1

128.72.x.x

128.72.55.4

128.84.x.x

128.84.73.1

3

4

56

1

198.100.9.7

5

198.101.84.21

Incominglabel

Outgoinglabel Address Prefix N/wInt.

X 2

198.101.x.x 4

198.101.x.x 3

Label Forwarding Table at 198.168.7.6

R3

R2

R1

R4


7/34


Copyright 2002-2005


Basic Concept of MPLS

Routing fills routing table

Signaling fills label forwarding table

DA Next hoprouter

N/wInt.

128.89.10.x 198.168.7.6 1

179.69.x.x 198.168.7.6 1

128.89.10.x

1

179.69.x.x

2

1

128.89.10.12

179.69.42.3

198.168.7.6

In

label

Outlabel

Address Prefix N/w

Int.

Advertises binding

Advertises binding

128.89.10.x5 1

179.69.x.x7 2

Advertises bindings

128.89.10.x3 1

179.69.x.x4 1

3

4

X

X

DA Next hoprouter

N/wInt.

128.89.10.x 128.89.10.1 1

179.69.x.x 179.69.42.3 2

Routing Table

In

label

Outlabel

Address Prefix N/w

Int.

Label Table

R1 R2

R3

R4


8/34


Copyright 2002-2005


Basic Concept of MPLS

128.89.10.x

1

179.69.x.x

2

1

128.89.10.12

179.69.42.3

198.168.7.6

In

label

Outlabel

Address Prefix N/w

Int.

In

label

Outlabel

Address Prefix N/w

Int.

128.89.10.x5 1

179.69.x.x7 2128.89.10.x3 1

179.69.x.x4 1

3

4

X

X

3

5

Packet arrives

DA=128.89.10.25

3Push

Label

5Pop

labelForward

packet

553

Swap

Label

R2R1

R3

R3 R4


9/34


Copyright 2002-2005


A Word on Network Layer Routing

Control

Plane

Forwarding

/Data Plane

Control Component

Responsible forconstruction and maintenanceof forwarding table. Consists of:

Routing protocols for exchange of routing info.

Algorithms to convert this into forwarding table

Forwarding/data ComponentAlgos. used to make forwarding decision on packet

The algorithms define:

Information from packet used to find an entry inthe forwarding table

Exact procedures used to find that entryFor unicast routing

Information = Network layer (IP) address

Procedure = Longest prefix matching


10/34


Copyright 2002-2005


So What about MPLS Control andForwarding?

Superset of conventional router control

Distribute routing info. via network layer routing (OSPF, BGP, etc.)

Algos. to convert routing info. into forwarding table for fwding component

Create binding from FEC (derived from routing info.) --> label

Assign and distribute labels to peer LSRs via signaling

Uses a label switching forwarding table (or LIB), looking as:

Forwarding algorithm = label swapping, independentof control

component (implementable in optimized hardware or software)

Control

Component

Forwarding

Component

First Subentry Second Subentry

(formulticast orload balancing)

Incoming Label Map

Next hop label forwarding entry (NHFLE)

Outgoing label

Outgoing inf.

Next hop address

Outgoing label

Outgoing inf.

Next hop address

Incoming Label


11/34


Copyright 2002-2005


What does a label represent?The issue of label granularity

Packets treated identically by participating routers form

Forwarding Equivalence Class (FEC

Assigned the same label

Membership of a FEC must be determinable from

IP header

Info. that ingress router has about the packet

Entities grouped into a FEC are flexible, and could involve

A connection between two IP ports on two hosts

All traffic between two IP hosts

All traffic headed for a particular network with same TOS bits

All destination networks with a certain prefix

All traffic headed to a particular router (e.g. an egress)

A manually configured connection and many others


12/34


Copyright 2002-2005


Lets Recap: Elements of MPLS

Label Forwarding

Use data link addressing, e.g. ATM VPI/VCI, FR DLCI

Put shim header between data link and IP header

Label Creation and Binding

Label Assignment and Distribution

Ride piggyback on routing protocols, where possible (BGP)

Use separate label distribution protocol RSVP, LDP/CR-LDP

Reliability: TCP or separate ACK/NACK

Variable

L2 header L3 IP headerMPLS shim

headerHigher Layers

4 bytes 20 bytes

Label CoS TTLS

20 bits 3 bits 8 bits

Data

Plane

Control

Plane

EXP/

1 bit


13/34


Copyright 2002-2005


Benefits over Conventional Routing

MPLS forwarding possible by:

Switches incapable of analyzing network layer headers

Unable to do so at adequate speeds

Ingress can use any info.about packet to assign to FEC/LSP

Conventional forwarding only considers info. in the packet

Forwarding decisions can depend on ingress router

Conventional routing, identity of ingress router does not travel with packet

Packet FEC assignment can use complex decision process No impact on forwarding of labeled packets!

Explicit routing packet need not carry encoding of entire route Unlike source routing in conventional IP forwarding


14/34


Copyright 2002-2005


MPLS Header over POS or IEEE 802.3

Label

(20 bits)

TTL

(8 bits)

EXP

(3 bits)

S

(1 bit)

4 octets

MPLS

Shim

Header

IP

HeaderIP Payload

Layer 2 Hdr

(e.g., PPP

or 802.3)

For labeled packets, Layer 2 header indicates whether it is MPLS

unicast packet or MPLS multicast packet

The label stack: sequence of 4-octet label stack entries (no limit

on stack depth)

Network layer packet immediately follows the label stack entry that

has the S bit set. Label values 0 -->16 are reserved


15/34


Copyright 2002-2005


MPLS Header over ATM

Top stack of shim carries placeholder label value of 0. VPI/VCI value in header

represent actual label value (no SNAP/LLC encapsulation used)

Upstream LSR connected to first ATM-LSR adjusts TTL value based on how

many ATM-LSRs are consecutively connected downstream (learnt via LDP)

For ATM LSRs, UNI gives 24-bit VPI/VCI label, NNI gives 28-bit VPI/VCI label

If two ATM-LSRs connected via VPC through ATM cloud, 16-bit VCI label used

Label=0

(20 bits)

TTL

(8 bits)

EXP

(3 bits)

S

(1 bit)

4 octets

MPLS

Shim

Header

IP

Header

IP PayloadAAL5 Trailer

(length, CRC-

32, ...)

ATM

Header

ATM

PayloadATM

Header

ATM

Payload

48 octets 48 octets

M i I


16/34


Copyright 2002-2005


Label Assignment and Distribution(Control Component)

Downstream Upstream

Ordered Solicited (On Demand)Unsolicited

SolicitedUnsolicited

Independent Solicited (On Demand)Unsolicited

SolicitedUnsolicited

Directionfrom which labels flow

Refers to whether LSR distributes

labels on demand or voluntarily

Whether LSR waits to hear from

its upstream/downstream nbrs.

before responding to a request

for label(s)

Label Retention: Liberal or Conservative

Whether LSR keeps labels from a neighbor

who is not currently the next hop for a FEC

Labels

Data

Labels

Data

M t i I


17/34


Copyright 2002-2005


Example Label Assignment andDistribution Modes

4

33

Edge LSR

Edge LSR

Downstream-on-demand

with Independent Control

1 Requests

2

2Assignments

Edge LSR

2

35

6

Edge LSR

Downstream-on-demand

with Ordered Control

1 Requests

4

Assignments

M t i I


18/34


Copyright 2002-2005


Comparison of ATM Switch, IPRouter, LSR, and Optical X-connect

ATMswitch

IP router LSR OXC

ControlPlane

Dynamic routingprotocol for

route exchange

PNNI BGP,OSPF, IS-IS, RIP

BGP,OSPF,IS-IS,

RIP

OSPF, IS-IS

Signalingprotocols

UNI, PNNI RSVP LDP/CR-LDP,extendedRSVP

LDP/CR-LDP,extendedRSVP

Data

Plane

Forwarding

Engine

ASICs Software,ASICs

Software,ASICs

ASICs

Switched entity ATM SVC,PVC.

IP packetsor flows

LSPs SONETchannels,Wavelengths,fibers

M t i I


19/34


Copyright 2002-2005


More on the MPLS Control Plane:Hop-by-hop Routed LSPs

LSPs whose routes are determined by IP routing protocolsShortest path, based on destination IP address of packet

Effectively creates labels for each route in forwarding table

Label distribution for hop-by-hop routed LSPs

LDP (Label Distribution Protocol)

Defined by IETF MPLS Working Group

LDP messages:

Notification, Hello, Initialization, KeepAlive, Address, Address Withdraw, Label

Mapping, Label Request, Label Withdraw, Label Release

Peer discovery msgs. over UDP, rest over TCP for reliability

Piggyback on existing IP routing protocols

Example: Add label information to BGP

Not all IP interfaces may be enabled for dynamic routing protocols

Metanoia Inc


20/34


Copyright 2002-2005


Hop-by-hop Routed LSP Setupusing LDP

Edge LSR

Edge LSR

Label Req.

Label Req.

Label Req.

Label Mapping.

Label Mapping.

Label Mapping.

LSR1 learns new IP

network prefix

1.1.1.0/24 via

dynamic IP routing

Each LSR forwards Label Req. along hop-by-hop routedpath to 1.1.1.0/24

Path established via a dynamic IP routing protocol

When next hop to 1.1.1.0/24 changes in LSR2 (e.g. due to

topology or link metric change)

LSR2 releases original LSP

Starts setting up new LSP from that point on

Several other options available

1.1.1.0/24.

Metanoia Inc


21/34


Copyright 2002-2005


ER-LSPs: Explicitly Routed LSPs

Routes determined by operators or n/w management appsBased on specific TE policy, QoS, or VPN membership

Significantly more efficient than conventional IP source routing

Label distribution for ER-LSPs

Extended RSVP (significantly different from original RSVP)

Associates labels with RSVP flows, supports aggregate flows

Control messages run on raw IP transport, requiring refreshes

CR-LDP (Constraint-based Routed LDP)

Now mostly of historical value

Metanoia Inc


22/34


Copyright 2002-2005


Strict ER-LSP Setup using CR-LDP

Edge LSR

Edge LSR

Label Req.

Label Req.

Label Req.

Label Mapping

Label Mapping

Label Mapping

Network operator or

network management

creates ER-LSP

request with path andtraffic parameters

Traffic parameter TLV contains: Frequency, weight

Peak data rate, Peak burst rate Committed data rate, committed burst rate, excess burst size

Frequency specifies granularity at which CDR is made available

Weight determines excess bandwidth possible above CDR

1.1.1.2 2.2.2.2

3.3.3.2

Metanoia Inc


23/34


Copyright 2002-2005


Loose ER-LSP Setup using CR-LDP

Edge LSR

Edge LSR

Label Req.

Label Req.

Label Req.

Label Mapping.

Label Mapping.

Label Mapping.

Network operator or

network management

creates ER-LSP

request with path and

traffic parameters

4.4.5.6 4.4.5.7

3.3.3.2

AS100

Metanoia Inc

A th i li ti f


24/34


Copyright 2002-2005


Are there any implications forhardware/ASICS?

Label stacking depth (if any) supported depends on hardware

processing capabilities and speeds

Hardware engine needs ability to examine both EXP bits and LABEL,

and map it to any control hardware used for scheduling MPLS

packets

Ability to push and/or pop labels determines whether switch can be

an edge LSR, or only a core LSR (doing only swapping)

Number of queues in the switch/router determines per-label queueing

or per-class queueing ability

Label merging capabilitydetermined by ability to re-assemble

packets from interleaved cells

Metanoia Inc


25/34


Copyright 2002-2005


Advantages of MPLS

Original justification was fast, amortized, ATM hardware

Eliminated by hardware forwarding engines at multi-gigabit rates

Current justifications include:

Separates forwarding from control, enabling

Evolution of routing functionality independently of forwarding algorithm

(which can continue to be label swapping)

Use of MPLS to control non-packet technologies like SONET/SDH

channels or optical light-paths

Facilitates scalable hierarchical routing(via label stacking)

Scalability by reducing number of IP peers/neighbors

Provides explicit, manageable IP routes: enablespolicy routingand

traffic engineering(can setup routes different than default shortest-path)

Metanoia Inc


26/34


Copyright 2002-2005


Reducing number of IP Peers

VCs between routers connected overATM network

O(n^2) VCs for full adjacency

O(n^4) routing info. exchange

overwhelms routers and network

LSR (runs

IP routing)

IP routing

peers

Interior switches participate in IProuting protocolsminimizes IP nbrs.

Eliminates full VC mesh for adjacency,

as LSRs run IP routing protocols

Router

ATM Switch

IP routing

peers

ATM Network

Metanoia Inc


27/34


Copyright 2002-2005


Hierarchical Label Stacking/Switching

Inside transit AS each interior router must keep trackof all networks reachable through it

With hierarchical labels, an arrangement is possible

where only Border Routers need to know whatnetworks might eventually be reached through them

All transit traffic can tunneled through interior routers

of the AS using LSPs with stacked labels

Metanoia Inc


28/34


Copyright 2002-2005


Utility of Hierarchical Label Switching

Interior LSRs

Border LSRs

Swap andPush

Pop

Swap

Metanoia, Inc.

E li it M bl R t


29/34


Copyright 2002-2005


Explicit Manageable Routes --Policy Routing, Traffic Engineering

Carriers want certain traffic to go overcertain routesThis type of network engineering:

Keeps network loads balanced

Enhances network stability and reliability

Enables better QoS and performance assurances

Allows carriers to meet SLAs

Constraint-based routing + MPLS

Allows carriers to bind specific traffic to an LSP

Place (or route) LSP over a desired sequence of LSRs

Metanoia, Inc.


30/34


Copyright 2002-2005


Constraint Based Routing

A class of routing systems that computes routes through a

network subject to a set of constraints and requirements

QoS-based Routing

Path of flows determined by

Knowledge of resource

availability in network

QoS requirements of flows

Policy-based Routing

Path/routing decision based

on administrative policy

Can be on-line or off-line

Metanoia, Inc.


31/34


Copyright 2002-2005


CB Routing System

Inputs

Flow/path attributes:

required b/w, hop count, ...

Resource attributes:

properties of nodes/links

Network topology & state

Outputs

Computed feasible path

Explicit route of the path

Constraint-Based

Routing Process

Attributes

Resources

Topology

Feasible Path

ERO {1,3,4,5}

1

3

4

5

2

Metanoia, Inc.

TE T l R l


32/34

,Critical Systems Thinking

Copyright 2002-2005


TE Topology versus RegularRouted Topology

A

B

C D

E

Network Diagram

Regular Routed

Topology

A

B

C

D

E

4

11

1

3

2

3

Link weights

A

B

CD

E

Traffic Engineering

Topology

OC-3

OC-12

OC-192OC-12

DS3

Best effort shortest

path from D to E

TE Path from D Eavoiding green linkswith at least STS-3 b/w

Metanoia, Inc.Automatic Reroute Using MPLS


33/34

,Critical Systems Thinking

Copyright 2002-2005


LSP ID = L2

Automatic Reroute Using MPLSRSVP-TE

Rerouting is done when

A better path is available

Upon failure along LSP

Use SESSION Obj. & SE style

Tunnel uniquely identified by

Destination IP address

Tunnel ID

Ingress IP address

Tunnel ingress made to appear

as 2 different senders to the

RSVP session (via LSP ID)

Src

Rcvr

LSP ID = L1

On these links the

LSPs share resources

Tunnel ID inSession Obj

Originates LSPs

with IDs 1 and 2

Here they are treated as different

LSPs within the same Session

LSPs 1 and 2 have a common SESSION Obj, but

a new LSP ID in the SENDER_TEMPLATE and a

different ERO (with possibly common hops)

Metanoia, Inc.

So what did we look at?


34/34

Critical Systems Thinking

Copyright 2002 2005 34

So what did we look at?Lets summarize

Looked at conventional IP routing and its limitations

Saw how labels decouple data plane from control plane

Examined basics of MPLS

Control and forwarding components

Label granularity (forwarding equivalence class, FEC)

Benefits over conventional routing

Label assignment and distribution methods

Downstream-on-demand, with ordered or independent control

Hop-by-hop routed LSPs, strict- and loosely explicitly-routed LSPs

Advantages of MPLS efficient hierarchical routing, reduces

number of IP peers, facilitates explicit routing

Use of MPLS for traffic engineering, protection, automatic

rerouting

Date post:	04-Apr-2018
Category:	Documents
Upload:	yousry-el-fowey
View:	216 times
Download:	0 times

MTNL MPLS Tutorial DrVishalSharma 2006-04-26

Documents