Odc010005 Mpls l2 VPN Issue1_1

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ODC010005 MPLS L2 VPN

ISSUE 1.1

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MPLS L2VPN provides layer 2 VPN services on the MPLS network. It allows the establishment of L2VPNs on different media including ATM, FR, VLAN, Ethernet and PPP. For users, the MPLS network is a layer 2 switching network and can be used to establish layer 2 connections between nodes. At the same time, the MPLS network can provide traditional IP services, MPLS L3VPN, traffic engineering and QoS.




References

l draft-kompella-l2vpn-l2vpn-01

l draft-martini-l2circuit-encap-mpls-10

l draft-martini-l2circuit-trans-mpls-17




Upon completion of this course, you will be able to:

[ Providing a architectural overview to MPLS L2 VPN

[ Giving a rough discussion to data flow of general MPLS L2 VPN

[ Providing a general discussion to Martini and Kompella signaling method




Chapter 1 What is MPLS L2 Chapter 1 What is MPLS L2 VPNVPN

Chapter Chapter 22 VLLVLL

Chapter Chapter 33 Layer 2 InterworkingLayer 2 Interworking




Traditional L2 VPN

l Leased Line

[Main shortcoming：long-time construction，expensive and difficult to manage it

l Virtual Circuit

[Comparing with LL，lower time construction、lower price

[Providing service on ATM or FR network，while the network need to be set up and maintained separately

[Low speed

[Complicated configuration




What is MPLS L2 VPN

l MPLS L3 VPN

l MPLS L2 VPN

Tunnel Label Inner Label Layer3 Header Data

Tunnel Label VC Label Layer2 Header Data

For CCC no VC Label For Layer2

interworking no Layer 2 Header




MPLS L2 VPN Network Structure

PEPE

Tunnel

Pseudo Wires

Customer Site

Customer Site

Customer SiteCustomer

Site

l The basic principle of all MPLS L2VPN modes, except CCC, is the same as the above shown.




MPLS L2 VPN Characters

l The service provider use MPLS network to provide Layer 2 services to the customer. It seems that CEs are connected directly or connected through layer2 switch networks, such as ATM, FR, Ethernet switch networks.

l Routing occurs between CE routers

l PE sends VPN traffic across the service provider ’s network to the PE router connected via LSP tunnels.




Advantages of MPLS L2 VPN

l High Scalability

l Separation of Administrative Responsibilities

l Routing Privacy and Security

l Ease of Configuration

l Native Multi protocol Support

l Signaling Flexibility

l Cost-efficient Migration from Traditional Layer 2 VPN










VLL

l VLL=Virtual Leased Line

l VLL provides layer 2 P2P connection between CEs.

l Implementation method includes:

[CCC

[Martini

[SVC

[Kompella




L2 VPN Common Packet Structure

[Tunnel Label−Ingress PE to Egress PE switching label−MPLS Label or GRE Tunnel

[VC Label−Identify different VC in the same tunnel

[Emulate VC Encapsulation (Control Word) − 32-bit Control Word

demultiplexerField

L2 PDU

(Emulated)

TunnelHeader

Connection

Control protocol

[ LDP、BGP、STATIC-LSP and so on− VC label’s negotiation, withdrawing and error notification

‘Emulated Circuits’—three layers encapsulation




PDU Structure

NPPPNHDLCYFrame RelayNEthernetYATM（AAL5）Control WordEncap type

Tunnel Label(LDP or RSVP)0 7 15 23 31

EXP 0 TTL

VC Label(VC) EXP 1 TTL(Set to 2)

Rsvd Flags 0 0 Length Sequence Number

Layer-2 PDU

Tunnel Label /VC Label

Control Word

Layer-2 Protocol Data Unit




PDU Structure Example-FR

lFrame Relay frame forwarded without Frame Relay header and FCS，then control word is necessary.

lThe useful information as BECN、FECN、 DE and C/R bits are carried through control flags

Tunnel Label(LDP or RSVP)

0 7 15 23 31

EXP 0 TTL

VC Label(VC) EXP 1 TTL(Set to 2)

Rsvd 0 0 Length Sequence Number

Layer-2 PDU

CDB F




ChapterChapter 22 VLLVLL

Section 1 CCCSection 1 CCC

Section 2 MartiniSection 2 Martini

Section 3 SVCSection 3 SVC

Section 4 Section 4 KompellaKompella




CCC Network Structure

MPLS Network

Branch Office A

PE

PE

PE

Branch Office A Branch Office A

Tunnel Label Layer2 Header Data

Local Connection

Remote Connection

Branch Office B

Headquarter B

Headquarter A

Only one level




Questions

l When local connection, there use Tunnel label or not?

l Each CE-CE there have two LSPs?

l When configuring LSP, we need to configure P router or not?












Martini Network Structure

MPLS Network

PE

MPLS Tunnel (LSP)

MPLS Tunnel (LSP)

PE

MP

LS Tunnel (LS

P)

Headquarter A

Outer Label VC Label

PE

VC Label distributed by LDP

Branch Office A

Branch Office A

Headquarter B

Branch Office B

Branch Office B

Layer2 Header Data




Draft for Martini

l The Mode is based on two drafts from Lucca Martini.

[draft-martini-l2circuit-trans-mpls

− VC label distribution, uses extended LDP

[draft-martini-l2circuit-encap-mpls

− Different encapsulation mechanism for different L2 circuit.




Martini Characters

l VC ID is used to identify a VC,VC Type indicates the encapsulation type.

l Martini Protocol extends LDP by adding VC FEC type including VC ID and VC Type. One label is allocated for per VC FEC.VC label has only local meanings.

l VC FEC and VC label is exchanged through targeted LDP session between two PEs.

l Tunnel between PEs can be used commonly by different VCs. Tunnel type can be LSP,TE tunnel or GRE tunnel.

l Can’t provide local connection.




VC FEC Format

VC TLV(0x80) c VC Type VC Info Length

Group ID

VC ID

Interface Parameters

0 0 LengthFEC TLV(0x0010)

Message ID

0 Label Message(0x0400) Message Length

0 0 LengthGeneric Label(0x0200)

Label

Optional Parameters

0 15 31




VC Status

l An In Label is allocated when a LDP VC is configured.

l If the Local State is up i.e.

l if the interface is up

l LDP Session is established

l at least one tunnel to destination exists

l then a mapping containing L2VPN Info like VC-ID, Interface type and other Interface parameters are sent to the destination.

l VC state is not up until it receives a mapping from the remote peer with matching VC ID, Interface type and parameters.

l With this mapping we also receive the in-label of the remote VC which is out-label for the local LDP VC.




Label Mapping

PE1 PE2

2. PE1 starts LDP session with PE2 if one does not already exist

CE1 CE2

1.L2 transport route entered on ingress PE

3. PE1 allocates VC label For new interface & binds To configured VCID

4. PE1 sends label mappingMessage containing VC FECTLV & VC label TLV

5. PE2 receives VC FEC TLV & VC label TLV thatMatches local VCID

PE2 repeats steps 1-5 so that bi-directional label/VCID mappings are established




Label Withdrawing

PE1 PE2

CE1 CE2

l If a PE route detects a condition that affects normal service, it must withdraw the corresponding VC label through the LDP signaling

Circuit status signaling PE port failure triggers Group ID withdraw

LDP label withdraw VCID20 VC label 100

CE port/VC failuretriggers Labelwithdraw Msg




Martini Summary

l LDP is the signaling to exchange VC FEC and VC Labels. VC ID is used to identify different L2VPN connection.

l Advantages:

[ Configuration is easy, it’s industrial trend.

l Disadvantages:

[ Can not provide local connection.




Questions

l Martini provide local connection or not? Why?

l As we know, two CEs which can set up the VPN connection need to be the same encapsulation type and CE ID, then on PE the in and out VC label is the same?












SVC

l SVC=Static Virtual Circuit

l Similar with Martini MPLS L2VPN, the only difference is In and Out VC Label is allocated manually. Targeted LDP session between two PEs is not needed for VC info exchange.

l VC state only depends on the local state and the tunnel state between two PEs.

l Tunnels are used to pass on the data packets between the PEs.




SVC Summary

l Similar with Martini MPLS L2VPN, the only difference is In and Out VC Label is allocated manually.

l Advantages: [ no signaling required.

l Disadvantages: [ can not provide local cross function ; the

number of SVC is strictly constrained by static label numbers.












Kompella Network Structure

MPLS Network

PE

MPLS Tunnel (LSP)

MPLS Tunnel (LSP)

PE

MP

LS Tunnel (LS

P)

Headquarter A

Outer Label VC Label Layer2 Header Data

PE

l2VPN Instance info distributed by BGP

Brach Office A

Brach Office A

Headquarter B

Brach Office BBrach Office B




Draft for Kompella

l Implemented through a draft from Keerti Kompella.

[draft-kompella-l2vpn-l2vpn-01

− Describes label distribution, uses BGP4

l Continue to use Martini draft for encapsulation

[draft-martini-l2circuit-encap-mpls




Kompella Control Plane

PE1PE2

CE1CE2

MP-BGP

PE1 sends out theconfigured VPN info

to neighbors withMP-BGP

PE2 receives theInformation and checks it

and calculate the VClabel with it




VPN Information－Label Block

1000

1001

1002

1003

1004

1005

1006

1007

1008

PE Label Block

CE1 Label Block1LB=1000LR=3LO=0



l PE chooses a Label Block.

l Label Base : Smallest Label in Block

l Range : number of labels of the block

l Offset: the sum of all the previous label blocks’ range.

l A remote site with CE ID m will connect to this CE with a label selected from one of the label blocks. block offset <= m < block offset + label-range Means m should be lower than the

total label range counts




Label Block Structure

Length

Route Distingguisher

CE ID

Label-block Offset Label Base

Label Base

0 7 15 23 31

Variable TLVs

l Circuit State Vector (CSV): variable TLV, used to identify the status of circuit.




Layer2-Info Extended Community

Extended Community type Encaps Type

Layer-2 MTU

0 7 15 23 31Control Flags

Reserved

l The extended community, Layer2-Info, Used to carry layer 2 specific information in a VPN. This extended community must be carried aspart of path attribute in all BGP update messages carrying L2VPNNLRIs.




VC Label Calculation-1

PE1 PE2

CE mCE k

L2VPNA (RD RT)CE mlabel-block : Lm Lm's block offset : LOmlabel-base : LBmlabel-range : LRm

L2VPNA (RD RT)CE klabel-block : Lk Lk's block offset : LOklabel-base : LBklabel-range : LRkMP-BGP




VC Label Calculation-2l Check the encapsulation type for VPN A, if does not match stop. (Note

that for IP-only layer 2 interworking a separate encapsulation type is defined).

l Check if k = m. If so, issue an error: Stop.

l Search among all the label-blocks from m for one which satisfies LOm<= k < LOm + LRm. If none found, stop. Otherwise let Lm be the label-block found.

l Search among all the label-blocks of k for one which satisfies LOk <= m < LOk + LRk. If none found, stop. Otherwise let Lk be the label-block found.

l The Interface bound with remote CE-m is identified based on the configuration in remote CE. Then VC label for sending packets to CE-m is (LBm + k - LOm) and The VC label on which to expect packets from CE-m is (LBk + m - LOk).




VC Calculation Example

PE1 PE3

PE2

CE2

CE3CE1

102

103

201 203

301

302

2001 PayloadTunnel

1002 PayloadTunnel

3001 PayloadTunnel 1003 PayloadTunnel

3002 PayloadTunnel

2003 PayloadTunnel

I have:VPN : redCE-id: 1Label Base: 1000Label Range: 10









Kompella Summary

l MP-BGP is used for signaling to transfer layer 2 NLRI and VC Label，use CE-ID to identify CE.

l Label Block is allocated based on the CE Range.

l Advantages:

[ Topology Auto-discovery; Support local cross ; Inter-as support.

l Disadvantages：

[ Implementation is complex; Venders who support this are less; Label Wastage.




Questions

l Does the static LSP used by CCC is the same with ordinary static LSP？

l What’s the relation between Martini and SVC？

l What’s the similarities and differences between Kompella and L3VPN？




L2VPN Characters Compare

SharedExclusiveSharedSharedTunnel Shared

Normal

ATM/FR/PPP/HDLC/ETH/VLAN

GRE/LSP/L2TPv3

NA

SVC

LowHighHighScalability




Encapsulation Type

Static LSPGRE/LSP/L2TPv3

GRE/LSP/L2TPv3

Tunnel Type

NALDPBGPSignaling

CCCMartiniKompellaModeIndex










Layer 2 Interworking

l As defined so far, all CE-PE connections for a given Layer 2 VPN must use the same layer 2 encapsulation, e.g., they must all be Frame Relay. This is often a burdensome restriction.

PE1 PE2

CE1CE2

FR LinkATM Link

Outer Label VC Label Layer3 Header Data




l The function of MPLS L2 VPN

l Basic principles of MPLS L2 VPN

l Signaling Method

SummarySummary



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Odc010005 Mpls l2 VPN Issue1_1

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