Oda000015 Mpls Basic Knowledge Issue2.0

7/31/2019 Oda000015 Mpls Basic Knowledge Issue2.0

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ISSUE

Fixed Network Curriculum

Development Section

ODA000015 MPLS BasicKnowledge

2.0


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2Confidential Information of Huawei.No Spreading without Permission. Security Level: Internal

Course Contents

Chapter 1 MPLS Overview

Chapter 2 Label and Label Stack

Chapter 3 Label Forwarding and Allocation

Chapter 4 LDP and Configuration


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MPLS

MPLSMulti-Protocol Label Switching

Multi-Protocol

Support multiple Layer-3 protocols, such as IP, IPv6, IPX, SNA

Label Switching Label packets, and replace IP forwarding with label switching


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Origin: To Integrate IP with ATM

Connectionlesscontrol plane

Connectionlessforwarding plane

IP

Connection-orientedcontrol plane

Connection-orientedforwarding plane

ATM

Connectionlesscontrol plane

Connection-orientedforwarding plane

MPLS


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Connectionless: packet route

Path 1 = S1, S2, S6, S8 Path 2 = S1, S4, S7, S8

The data reach their destinationout of order along different paths

connection-oriented: cell switching

VC = S1, S4, S7, S8

The data reach their destination inorder along the same connection

Fixed time delay, easy to control

Connection types: PVC SVC

S2 S6

S4 S7

S3 S5

S1 S8

1

1

1

2 2

2

S2 S6

S4 S7

VC

S1 S8S3 S5

Connection-oriented Features


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Traditional IP Forwarding

Parse IP headermapped to next hop



IP header is parse at each hop, resulting in low efficiency.

It is hard to deploy QoS and the efficiency is rather low.

All routers are expected to know all routes in the entire

network.


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Virtual Channel Connection

(VCC)

Virtual Path Connection(VPC)

VPswitching

VCswitching

VCswitching

NNI NNI

VPI = 2VCI = 44

VPI = 1VCI = 1

VPI = 26VCI = 44

VPI = 20VCI = 30

UNIUNI

ATM Switching Process

Connection-oriented, N2 problem

Routing depending on link layer, based on VPI/VCI or label

Ensure QoS and real-time service


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+ XR = X

Router ATM switch MPLSRouter

MPLSmulti-protocol label switching

Layer 3 routing scalable and flexible

Layer 2 switching High reliability and traffic engineering

management

Technology Combining the Advantages of ATM and

IP


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Core LSR

Basic Working Process of MPLS

IP IP L1 IP L2 IP L3 IP

Traditional IPforwarding

TraditionalIP forwarding Label forwarding

Edge LSR Edge LSR


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Basic MPLS Concepts

LSR: Label Switch Router

LER: Label Edge Router

LSP: Label Switch Path

LER

LER

LER

LER

LSR LSR

LSR

MPLS domain

IP

MPLS

LSP


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MPLS Advantages

Replace IP header with short and fixed-length labels as

forwarding basis to improve forwarding speed

Better integrate IP with ATM better

Provide value-added service without prejudice to efficiency:

VPN

Traffic engineering

QOS


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Course Contents






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MPLS Encapsulation Format and Label

MPLS headerLayer 2header IP header Data

Label SEXP TTL

200 23 24 31

32 bits

Two types of MPLS encapsulation for ATM and FR:

shim encapsulation: similar to other link layers Cell mode: VC (VPI/VCI for ATM, DLCI for FR) is directly

used as the label


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Label Position in Packet

Ethernet header/PPP header Label Layer-3 data

Ethernet/SONET/SDH packet

ATM header Label Layer-3 dataFrame modeATM packet

Cell modeATM packet VPI/VCI Layer-3 data


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MPLS TTL Processing

Regard the entire MPLS domain as one hop

IP TTL --MPLS TTL255 MPLS TTL -- IP TTL --

Ingress LER LSR Egress LER

Include MPLS TTL in IP TTL

IP TTL --MPLS TTLIP TTL MPLS TTL --

MPLS TTL --IP TTLMPLS TTL

Ingress LER LSR Egress LER


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Confidential Information of Huawei.No Spreading without Permission. Security Level: Internal

Label Stack

Theoretically, label stack enables limitless nesting toprovide infinite service support. This is simply thegreatest advantage of MPLS technology.

MPLSheader

Layer2header IP header Data

MPLSheader


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Course Contents






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Basic Concepts of Label Forwarding

FEC (Forwarding Equivalence Class): Import the packets

with identical characteristics into the same LSP

NHLFE (Next Hop Label Forwarding Entry): Describe label

operations

next hop

label operation types: push/pop/swap/null

Link layer encapsulation types

FTN (FEC to NHLFE): Map FEC to NHLFE

ILM (Incoming Label Map): Map MPLS label to NHLFE


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Label Forwarding

Parse IP headerFEC bound with LSPFTN->NHLFE

ILM->NHLFE

ILM->NHLFEParse IP headerdistribute FECmapped to next hopILM->NHLFE

Ingress LER LSR LSR Egress LER

Label operation: push

Label operation: swapLabel operation: swap

label operation: pop

The traditional routing protocol and Label Distribution Protocol (LDP) serve to create routing table and label

mapping table (FEC-Label mapping) in each LSR for FECs with service requirement, i.e. create LSPsuccessfully.

Ingress LER receives a packet, determines the FEC that the packet belongs to, and label the packet

In MPLS domain, packets are forwarded in accordance with labels and label forwarding table via the

forwarding unit

Egress LER removes the label and continues forwarding the packet

A B C D


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NHLFE

A:

Add label L1E1B10.0.1.0/24

OthersLabel operationTransmitting interfacenext hop

NHLFEFEC

Remove the previous label and add L2E1CL1

Otherslabel operationTransmitting

interfaceNext hop

NHLFEIngresslabel

B,C:

Remove labelDL2

OthersLabel operationTransmittinginterface

Next hop

NHLFEIngresslabel

D:


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Pop at Last Hop But One (PHP)

Parse IP headerDistribute FECMapped to next hop

Label operation: popParse IP headerFEC bound with LSPFTN->NHLFE ILM->NHLFE ILM->NHLFE

Ingress LER LSR LSR Egress LER

Label operation: pushLabel operation: swap

The label at the outmost layer does not make any sense to the last hop. Thus, it

is advisable to pop the label at the last hop but one to ease the burden of the

last hop.

If there is only one layer of label, the last hop will perform IP forwarding directly;

otherwise, it will perform the internal label forwarding.


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Creating LSP

LSP drive modes:

Driven by stream: incoming packets drive LSP creation

Driven by topology: topology information (route) drives LSP

creation

Driven by application: application (like QoS) drives LSP creation

Signaling protocol is used to distribute labels between LSRs

and establish LSP:

LDP: Label Distribution Protocol

CR-LDP: Constrained Route LDP

RSVP-TE

MP-BGP

PIM

S l I C i


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Several Issues ConcerningLabel Distribution

Label allocation mode

DoD : downstream-on-demand

DU: downstream unsolicited

Label control mode

Ordered

Independent

Label hold mode

Conservative retention mode : upon receiving a label, if there is

no route destined for the corresponding FEC, hold the label for

later use

Liberal mode: upon receiving a label, if there is no route

destined for corresponding FEC, discard the label


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Label Allocation Mode: DU

UpstreamDownstream

Routetriggering

Once the LDP session is set up successfully, the downstream

LSR will initiatively advertise the label mapping message to its

upstream LSR.The upstream router will save the label in the label mapping table.

171.68.10/24

20Label 20 can be usedto reach 171.68.10/24

171.68.10/24171.68.40/24

171.68.10/24

18

Label 18 can be usedto reach 171.68.10/24


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Label Control Mode: Ordered

Upstream Downstream

Not until it receives a label mapping message from its

downstream LSP will it send the message upstream


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Label Control Mode: Independent

UpstreamDownstream

Whether it receives a label mapping message from its downstreamLSR, it will send upstream a label mapping message immediately.


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Label Retention: Conservative Retention Mode

LSR1 LSR2 LSR3 LSR4

LSR5

172.16.2/24

mapping

label 20mapping

label 30

mapping

label 17

mapping

label 16

Drop

An LSR stores only the labels received from next-hop

LSRs; all other labels are ignored.


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Label Retention: Liberal Retention Mode

LSR1 LSR2 LSR3 LSR4

LSR5

172.16.2/24

mapping

label 20mapping

label 30

mapping

label 17

mapping

label 16

store

Every LSR stores the received label in its LIB, even when the

label is not received from a next-hop LSR.

Common Collocation 1


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Common Collocation 1:DoD + Ordered + Liberal

Upstream Downstream

It is relatively easy to control the use of labels and the

creation of LSPs

ATM/FR frame mode can only use DoD

Common Collocation 2:


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Common Collocation 2:DU + Ordered + Conservative

Upstream Downstream

A waste of label resources

Useless LSPs would be created

Label merge is required at branches

LSPs can be set up quickly and reliably


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Label Forwarding Table

IN interface IN label Prefix/MASK OUT interface (next hop) OUT label

Serial0 50 10.1.1.0/24 Eth03.3.3.3 80

Serial1 51 10.1.1.0/24 Eth03.3.3.3 80

Serial1 62 70.1.2.0/24 Eth03.3.3.3 52

Serial1 52 20.1.2.0/24 Eth14.4.4.4 52

Serial2 77 30.1.2.0/24 Serial35.5.5.5) 3pop

The in and out is correspond to the label swap not

the label distribution.

The in label is that I distribute to the others, I will not put it

to the packet

The out label is the others distribute to me, I will put it to

the packet


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LSP Loop Detection

Path looping shall be avoided even in setting up

LSP within the MPLS domain.

LSP path looping can be avoided in two ways:

Maximum hop number;

Path vector


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Basic Concepts of LDP

LDP is a MPLS control and signaling protocol

Main functions:

Release Label-FEC mapping

Create and maintain label switching path

LDP serves to distribute and maintain label mapping

messages between peers in the form of message.

LDP uses the TCP transmission service.


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LDP Message Types

Discovery message: Used to discover LDP adjacencies

in the network

Session message: Used to set up, maintain and

terminate a session between LDP peers

Distribution message: Used to create, change and

delete label mappings related to FEC

Notification message: Used to provide recommendation

or error notification information


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LDP Message Switching

UDP-Hello

UDP-Hello

TCP connection establishment

Label requestFEC

Label mapping

Label

Session initialization

Discovery stage

Session creationand maintenance

LSP creation andmaintenance


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Basic MPLS Configurations (1)

Designate ID for LSRIt is necessary to configure the LSR with an ID before configuring

other MPLS commands. The ID is generally in the format of IP

address, and shall be unique within the domain.

mpls lsr-id X.X.X.XNote: make configurations in the system view.

Activate/deactivate the LDP or enter the LDP view

To configure LDP, first activate the LDP and enter the LDP view

mpls ldp

Note: make configurations in the system view


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Basic MPLS Configurations (2)

Enable interface LDP

mpls ldp enable

Note: make configurations in the interface view

LDP loop detection control

Enable loop detection

Loop-detect

Set the maximum hot number for loop detection

hops-count hop-number Set the maximum value for the path vector

ath-vectors pv-number

Note: make configurations in the LDP view


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MPLS Debugging

MPLS display commands

Display information about LDP and LSR

display mpls ldp

Display information about LDP-enabled interface

display mpls ldp interface

Display information about all LSPs established in the public

network

display mpls lsp


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Configuration Example

Suppose a network consists of four NE routers, where Router B is connected to

Router C via SDH, while Router B is connected to Router A and Router D via

Ethernet.

The four routers all support MPLS. LSP can be set up between any two routers. The

operational routing protocol is OSPF

Router B

Router A

Router C

Router D

ethernet8/0/0

168.1.1.1

ethernet1/0/0

168.1.1.2

ethernet1/0/1

172.17.1.1

ethernet2/0/1

172.17.1.2

pos2/0/1

100.10.1.2

pos7/0/0

100.10.1.1

Configuration procedure

Configure ip address for

the interface

Configure the ospf

protocol

Configure the MPLS LDP

Router C is configured with:[Quidway] interface pos 7/0/0[Quidway-Pos7/0/0] ip address 100.10.1.1

255.255.255.0[Quidway] router id 172.16.1.2[Quidway] ospf[Quidway-ospf] area 0[Quidway-ospf-area-0.0.0.0] network 100.10.1.00.0.0.255[Quidway] mpls lsr-id 172.16.1.2[Quidway] mpls ldp

[Quidway-Pos7/0/0] mpls ldp enable


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Summary

Grasp the basic concepts and working process of MPLS

Grasp label allocation and distribution

Grasp MPLS LDP configuration


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Oda000015 Mpls Basic Knowledge Issue2.0

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