03-Packet Service Carrying Technologies of MSTP+ Products

06.April 2006

HUAWEI TECHNOLOGIES Co., Ltd.

www.huawei.com

HUAWEI Confidential

INTERNAL

Packet Service Carrying Technologies

of MSTP+ ProductsMSTP Product Team, Network

Product Service Dept.

HUAWEI TECHNOLOGIES Co., Ltd. Page 3HUAWEI Confidential

With an intention to introduce the technologies used to carry the packet services on the MSTP+ equipment, this course consists of three parts, that is, MPLS technology, PWE3 technology, and QinQ technology.

Preface


Before taking this course, you should

have the following knowledge: Basic concept of L2VPN

Basics on TCP/IP

Basic concept of the IP network

Guidance


References

ITU-T G.8110IETF RFC 3031IETF RFC 3032IETF RFC 3036IETF RFC 3209


After taking this course, you are supposed to reach the following objectives:

Understand the basic concept of MPLS

Understand the networking scenario of the MPLS LSP on the MSTP+ equipment

Understand the principle and application scenario of the PWE3 technology

Understand the basic principle of QinQ

Understand the typical application of QinQ

Objectives


Part 1 MPLS TechnologyPart 1 MPLS Technology

Part 2 PWE3 Technology

Part 3 QinQ Technology


Concept of Tunnel

A tunnel functions as a path between two network nodes. Data can be

transparently transmitted over the path.

Tunnel

RT1 RT2 RT3 RT4

On a PSN, multiple tunnel transport technologies are available. On an MPLS network, the MPLS is used to provide tunnels.


Introduction to MPLS

Originating from IPv4, multi-protocol label switching (MPLS) is intended to combine IP and

ATM.•Multi-protocol: Multiple Layer 3 protocols are supported, such as IP, IPv6, IPX, and SNA.•Label switching: Labels are stuck to packets so that label switching takes place of IP forwarding.MPLS is not a service or application, but a tunnel technology

Connectionless control plane

Connectionless forward plane

IP

Connection-oriented control

plane

Connection-oriented forward

plane

ATM

Connectionless control plane

Connection-oriented forward

plane

MPLS


LER

LER

LER

LER

LSR LSR

LSR

MPLS domain

IP

MPLS

Structure of an MPLS Network


LSP

Ingress Egress

Core LSR

MPLS network

Transit Transit

LER LER

Non-MPLS network

Core LSR

Non-MPLS network

Concept of MPLS

Ingress: ingress node

Egress: egress node

Transit: intermediate switching node

Label edge router

Label switch router

Label switch path


MPLS Encapsulation Format and MPLS Label

Not limited to any specific link-layer protocol, MPLS can transport packets over

any Layer 2 media.

Generally, an MPLS shim is added behind the link layer. The type domain of the

link layer is indicated as MPLS.

Ethernet Eth Header DataShim Header


Format of the MPLS Label

The MPLS header contains 32 bits (4 bytes) and consists of the following fields:•Label: 20 bits•Experimental: 3 bits, which indicate the class of service (CoS)•S: 1 bit, which indicates presence of a stack bottom and functions for label embedding•TTL: 8 bits

MPLS headerLayer 2 header IP header Data

Label SEXP TTL

200 23 24 31

32 bits


Label Stack

In theory, a label stack enables unlimited label embedding so as to support services

with no limitation. This is the most shining highlight of MPLS.

MPLS header

Layer 2 header IP header Data

MPLS header


Concept of Label Switching Label

A label is a locally significant identifier and is short and of a fixed length. A label is always located between the encapsulation header of the data link layer and Layer 3 data package. A label maps FEC through binding.

FECForwarding equivalence class (FEC) refers to a class of packets, all of which are treated as the same during forwarding. As stipulated by the MPLS initiator, an FEC can be identified and created through the address, tunnel, of CoS. This essence, however, is not comprehended by the successors. As a result, in the case of the current MPLS, one route corresponds to one FEC. Generally, on the same equipment, the same label is allocated to one FEC.

LSPA definite label is allocated to an FEC data stream at each node so that data forwarding is based on the labels. The path over which the data stream travels is referred to as an LSP.

LSRAs the core switch of an MPLS network, label switching router (LSR) has the functions of switching and distributing labels.

LERAt an edge of an MPLS network, an label switching edge route (LER) classifies the incoming traffic of the MPLS network to different FECs and requests for certain labels of the FECs. An LER has the functions of classifying traffic, mapping labels, and removing labels.


MPLS Label Switching Process

LER

LER

IP

IP

Push

Swap

Swap

Pop


Why MPLS?

In the case of MPLS, packets are forwarded according to the short labels of a

fixed length to speed up data forwarding. In this manner, a value-added service is

provided without expense of efficiency.Application of VPN tunnels: L2VPN and L3VPNTraffic engineering: MPLS-TEQOS: Diff-Serv, DS-TE


47.1

47.247.3

IP 47.1.1.1

Dest Out47.1 147.2 247.3 3

1

23

Dest Out47.1 147.2 247.3 3

1

2

1

2

3IP 47.1.1.1

IP 47.1.1.1IP 47.1.1.1

Hop-by Hop Forwarding of IP

In the case of hop-by-hop forwarding of IP, each hop searches the routing table for a proper route according to the longest match routing rule (maybe for several times). Hence, the forwarding is slow.

DEST OUT

47.1.0.0 1

47.0.0.0 1

47.1.1.0 1


Label Switched Path (LSP)

In the case of MPLS label forwarding, labels are allocated in advance and then an LSP is created for packets according to the labels. Then, each node along the LSP only needs to quickly switch labels (one-time search).

Intf In

Dest Intf Out

Label Out

3 47.1 1 50

Intf In

Label In

Dest Intf Out

3 40 47.1 1

Intf In

Label In

Dest Intf Out

Label Out

3 50 47.1 1 40

47.1

47.247.3

1

2

31

2

1

23

3

IP 47.1.1.1

IP 47.1.1.1


An MPLS network consists of an outer layer and an inner layer. The outer layer consists of LERs with powerful packet processing capabilities. When accessing IP packets, an LER searches the label forwarding table and performs the "push" operation on the IP packets. When the IP packets leave the network, an LER perform the "pop" operation on the label stack of the IP packets. The inner layer consists of LSRs with weak packet processing capabilities. The LSRs performs quick "swap" operations on the label stack of the IP packets.

Structure of an MPLS Network

MPLS LER

LSP

MPLS LER

Ingress

Egress


Label Forwarding - Push

When receiving packets, the ingress LER determines the FEC that the packets belong to, pushes labels on

the packets, and sends the encapsulated MPLS packets to the egress and finally to the next hop.

Ingress LER LSR LSRA B C D

LSR LSRA B C D

Egress LER

Label operation: pushAnalyzes the IP header.Binds FEC with LSP. Label operation: swap Label operation: swap

Label operation: popAnalyzes the IP header.Maps packets to the next hop..

A:

…E1B

NHLFEFEC

A:

…Push label L1E1B10.0.1.0/24

OthersTransmit PortNext hop

NHLFEFEC

Label operation


Label Forwarding – Swap

At a transit node, the forwarding unit forwards the packets only according to labels and the label forwarding table.

LSR LSRA B C D

Ingress LER

Label operation: pushAnalyzes the IP header.Binds FEC to LSP.

Label operation: swap


Label operation: popAnalyzes the IP header.Maps packets to the next hop.

Egress LER

…Remove the original label and stick

the L2 label.GECL1

Label OperationTransmit Port

NHLFEIngress Label

…GEC

OthersNext Hop

B and C:


Label Forwarding – Pop

The egress LER removes the label and forwards the packets.

LSR LSRA B C D

Ingress LER

Label operation: push: Analyzes the IP header .Binds FEC to LSP .

Label operation: swap: :

Label operation: popAnalyzes the IP header.Maps packets to the next hop.

Egress LER


…Remove the label.DL2

OthersNHLFE

D:

Ingress LabelNext Hop Transmit Port Label Operation


Label Forwarding Table

In the label forwarding table, "IN" and "OUT" are significant for label forwarding.• An IN label is allocated by a local node for another node and an OUT label is allocated by

another node to the local node.• An IN label is not stuck to the packets. • The labels allocated by the same equipment are unique. Hence, the labels vary with

equipment.

IN Interface IN Label Prefix/MASK OUT Interface (Next Hop)

OUT Label

Serial0 50 10.1.1.0/24 Eth0 （ 3.3.3.3） 80

Serial1 51 10.1.1.0/24 Eth0 （ 3.3.3.3） 90

Serial1 62 70.1.2.0/24 Eth0 （ 3.3.3.3） 52

Serial1 52 20.1.2.0/24 Eth1 （ 4.4.4.4） 52

Serial2 77 30.1.2.0/24 Serial3 （ 5.5.5.5) Null （ pop）


LSP Setup

The MPLS protocol needs to allocate labels to service packets in advance so as to set up an LSP, over which the service packets are forwarded. How does the MPLS protocol set up an LSP and allocate labels?

1. Static LSP

The user needs to allocate a label for each FEC to set up an LSP. The administrator needs to

manually perform configuration at each station. When manually allocating labels, adhere to the

principle that the value of the OUT label of the previous node is the value of the IN label of the next

node.

2. Dynamic LPS (not supported currently)

The routing protocol and label distribution protocol dynamically sets up a dynamic LSP.

Label distribution protocol:

LDP (used by MSTP+ equipment to set up PWs)

RSVP-TE (used by MSTP+ equipment to set up TE tunnels)

MP-BGP (used by MSTP+ equipment to set up L3VPNs)


Part 1 MPLS Technology

Part 2 PWE3 TechnologyPart 2 PWE3 Technology

Part 3 QinQ Technology


Contents

Overview of PWE31.1 Basic Concept1.2 PWE3 Reference Model1.3 PWE3 Protocol Stack Reference Model


What is PWE3?

As a technology used to carry end-to-end Layer 2 services, pseudo wire emulation end-to-end (PWE3) is intended to emulate virtual end-to-end links for various services, such as FR, ATM, Ethernet, TDM, SONET, and SDH services, at the edges of the PSN. The PWE3 technology enables interconnection of the traditional network with the PSN. Hence, the resources can be shared and the network can be expanded.

PEPE

PE

CE CE

CE

AC

PW1PW2

PW3


What is PW?

The MSTP+ equipment has the following functions with respect to pseudo wire (PW) :

•Encapsulates cells, PDUs, or specific service bit flows at the ingress port.

•Transports the cells, PDUs, or specific service bit flows over the IP or MPLS network.

•Creates a PW at the terminal point of a tunnel, and switch and allocate PW IDs.

•Manages the service-related information such as signaling, timing, and sequence at the

edge of the PW.

•Manages the service alarms and status.


Basic Transport Components of PWE3

CE3

CE4

VPN 1Site 2

PE1

P

PE2

ACPWTunnel

MPLS network

CE2

CE1

VPN 1Site 1

VPN 2Site 2

VPN 2Site 1

PW signaling protocol

Forwarder


Attachment circuit (AC)An AC refers to a physical or virtual link attaching a CE to a PE. All packets on an AC, including Layer 2 and Layer 3 protocol packets, must be forwarded to the opposite site without any change.

Pseudo wire (PW)To put it simply, a PW is a virtual connection (VC) in a tunnel, which can be an LSP, L2TPV3, or TE, and is directional. In the case of PWE3, the signaling (LDP or RSVP) is used to transfer the VC information, and then a PW is set up according to the VC information and tunnel management information. For a PWE3 system, a PW is similar to a direct tunnel from the local AC to the opposite AC. Over the PW, the Layer 2 data of users is transparently transported. A PW can be simply considered as a service.



ForwardersWhen receiving data frames over an AC, the forwarder selects a proper PW for the

packets. In this manner, the forwarder functions as a forwarding table for PWE3.

TunnelsTunnels are used to carry PWs. One tunnel can carry multiple tunnels. Generally, a

tunnel is an MPLS tunnel.

A tunnel is a direct channel between a local PE and opposite PE, over which data is

transparently transported between PEs.

On the PTN equipment, a tunnel is unidirectional but a PW is bidirectional. Hence,

one PW requires two MPLS tunnels so as to carry services.



EncapsulationThe packets transported over a PW are encapsulated in the standard PW format by using the standard PW technology.As defined in draft-ietf-pwe3-iana-allocation-X, there are multiple encapsulation modes for the PWE3 packets over a PW.

PW signalingAs a basis to realize PWE3, the PW signaling protocol is used to create and maintain PWs. Currently, the PW signaling protocols include the LDP and RSVP.

Service qualityThe priority information of the Layer 2 header of user packets is mapped to the QoS priority information, which is then transported on the public network for forwarding. In this case, the MPLS QoS must be supported for the application.



PWE3 Reference Model

PE1

CE1 Tunnel CE2

Emulated service

Pseudo wire

PSN tunnel

PE2

Native service

Native service

Customer edge 1

Custom edge 2

Provider edge 2

Provider edge 1

AC AC

AC: attachment circuit


PWE3 Protocol Stake Reference Model

Payload encapsulatio

n

Emulated service

(TDM, ATM, Ethernet,

and others)

PW demultiplex

er PSN tunnel, PSN & physical

layers

Emulated Service

Pseudo wire

PSN Tunnel

Payload encapsulatio

n

Emulated service

(TDM, ATM, Ethernet,

and others)

PW demultiplex

er PSN tunnel, PSN & physical

layers

PSN

RTP

Sequence number

PW label

LenFragFlags

Outer label or MPLS-in-IP encapsulation

RTP

Sequence number

PW label (L2TP/MPLS)

LenFragFlags

IP

MAC


ETH PWE3 Reference Model

Emulated Ethernet(including VLAN)

service

Demultiplexer

PSNMPLS/IP

Physical

Emulated Ethernet (including VLAN)

service

Demultiplexer

PSNMPLS/IP

Physical

Emulated service

Pseudo wire

PSN tunnel

PSN


ETH PWE3 Encapsulation Format

0 1 2 3

0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

PSN transport header in PWE3

Pseudo wire header in PWE3

0 0 0 0 Reserved Sequence number

ETH payload


lub UP

802.1Q

Eth

PWE3

MPLS

---

Line interface Line interfaceNetwork interfacelub UP

802.1Q

Eth

N:1 Eth PWE3 Encapsulation

PSNPSN

EF

AF3

BE

Legend

1+1/1:1 APS

Tunnel

lub UP

802.1Q

Eth

PWE3

GE/FE

lub UP

802.1Q

Eth

GE

PoC3 PoC1

E1/POS/GE

3G Node B

RNC

Multi-Service Carrying: IP/ETH Traffic Solution


Part 1 MPLS Technology

Part 2 PWE3 Technology

Part 3 QinQ TechnologyPart 3 QinQ Technology


► To solve the problem of insufficiency in VLAN IDs on the public network—————————————————————————The 4096 VLAN IDs are insufficient for a large-scale network, but the operator need to identify users according to VLAN IDs.

► To enable the users to plan VLAN IDs of their private networks without the possibility of a conflict with the VLAN IDs on the public network—————————————————————————The two-layer VPN technology enables transparent transmission of the VLAN information and Ethernet configuration information of users.

The QinQ technology is intended to solve the problem of insufficiency in VLAN IDs on the public network and to provide a simple two-layer VPN solution for small metropolitan networks or enterprise networks.

Background of QinQBackground of QinQ

Basics of the QinQ Technology



QinQ refers to the practice of sticking another tag before the tag of the packets encapsulated in the

802.1Q format or identifying tunnels (users) by the previous tag.

Currently, the network equipment of multiple suppliers supports the QinQ feature with different

names:

HUAWEI VLAN VPN

Cisco 802.1Q Tunneling

Extreme Virtual MAN/vMANs

Riverstone Stackable VLAN/SVLAN

The basic notion of the QinQ feature is to encapsulate the VLAN tag of a user private network into

the VLAN tag of the public network. Then, the packets, with two tags, traverse the backbone network

of the service provider. In this manner, a simple two-layer VPN tunnel is provided to users.

Basic Notion of QinQBasic Notion of QinQ


DADA SASA TypeType DataData CRCCRC

Standard Ethernet frameStandard Ethernet frame


Standard 802.1QStandard 802.1Q Ethernet frameEthernet frame


TagTagTPIDTPID

TagTagTPIDTPIDTagTagTPIDTPID

QinQQinQ EncapsulationEncapsulation

QinQQinQ Ethernet frameEthernet frame


Compared with the standard 802.1Q Ethernet frame, the QinQ Ethernet has one more tag, which is referred to as an outer tag.

This tag is referred to as an inner tag, which is stuck by the user.


SS

SSSS

SS

SS

SS

SSVLAN100

VLAN200

Client A

ISP operator network

VLAN100

VLAN200

Tunnel port: outer tag stuck or removed

Trunk port: one tag on the client side and two tags on the operator side

Basics of the QinQ TechnologyTypical Application of QinQTypical Application of QinQ

Header DataUservlan

10Header DataUservlan Header DataUser

vlan

Outer tag

20Header DataUservlan

Client B


Advantages of QinQ

QinQ simply means two 802.1Q tags stuck on packets.

The QinQ technology enables the operator to provide a two-layer VPN for customers with low costs. QinQ is performed only on the operator network and thus is not visible to the users.

In the case of the packets on the operator network, the inner tags are the user-specific VLAN tags and the outer tags are the VLAN tags assigned by the operator to users. The clients can plan VLAN IDs independently. The changes in the operator network do not affect the client networks.

QinQ does not require an independent signaling protocol, but static configuration. Therefore, QinQ is simple and stable.

QinQ expands the VLAN resources and enables the operator to identify users by VLAN IDs.

06.April 2006

HUAWEI TECHNOLOGIES Co., Ltd.

www.huawei.com

HUAWEI Confidential

INTERNAL

Thank Youwww.huawei.com

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03-Packet Service Carrying Technologies of MSTP+ Products