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Questions and Answers

What is MPLS generally referred to as?

Layer 2.5 protocol (correct)

Layer 4 protocol

Layer 2 protocol

Layer 3 protocol

What does MPLS use to make data forwarding decisions?

ATM Headers

IP Headers

Route Headers

Labels (correct)

What is the role of the customer edge switch in an MPLS-based Layer 2 VPN?

Providing converged services to users

Forwarding traffic to the service provider's provider edge switch (correct)

Addressing quality of service issues

Analyzing Layer 3 headers

What is one of the benefits of MPLS-based VPNs?

Scalability Signup and view all the answers

What is the format of traffic that is forwarded by the customer edge switch in an MPLS-based Layer 2 VPN?

Layer 2 format Signup and view all the answers

What is the goal of MPLS in the context of Class of Service and Quality of Service?

To address issues related to Class of Service and Quality of Service Signup and view all the answers

What is the advantage of using MPLS in terms of Layer 3 header analysis?

Layer 3 header analysis is done just once Signup and view all the answers

What is the primary function of the provider edge switch in an MPLS-based Layer 2 VPN?

To receive traffic from the customer edge switch Signup and view all the answers

What is carried by MPLS over the service provider's network?

Layer 2 VPN Signup and view all the answers

Where does routing occur on a Layer 2 VPN?

Customer's CE switches Signup and view all the answers

What must the CE switch select to send traffic in a Layer 2 VPN?

The appropriate circuit Signup and view all the answers

What do the PE switches do with the customer's routes in a Layer 2 VPN?

Do not store or process them Signup and view all the answers

Who is responsible for configuring their own switches to carry all Layer 3 traffic in a Layer 2 VPN?

Customer Signup and view all the answers

What is the service provider's role in a Layer 2 VPN?

To detect how much traffic the Layer 2 VPN will carry Signup and view all the answers

What is a Layer 2 circuit?

A point-to-point Layer 2 connection Signup and view all the answers

What is required to connect each PE switch to each CE router or switch in a full-mesh Layer 2 VPN?

One physical link Signup and view all the answers

What is the primary benefit of Layer 2 VPNs for customers?

Customers can maintain control over most of the administration of their networks Signup and view all the answers

What is the purpose of the VPN Forwarding Tables (VFTs) in Draft-Kompella?

To populate the information provisioned for the local CEs Signup and view all the answers

How are VCTs distributed in Draft-Kompella?

Via MP-iBGP Signup and view all the answers

What is the purpose of the DLCIs in Draft-Kompella?

To provision the customer sites on the PE Signup and view all the answers

What is the difference between Draft-Kompella and Draft-Martini?

Draft-Kompella uses MP-iBGP, while Draft-Martini uses LDP Signup and view all the answers

What is the purpose of the VCTs in Draft-Kompella?

To configure the VPN topologies Signup and view all the answers

Which of the following is a supported Layer 2 technology in Draft-Kompella?

Frame Relay Signup and view all the answers

What is the primary function of the PE device in Layer 2 VPNs?

To map the circuit ID to an MPLS LSP Signup and view all the answers

What is a requirement for a PE-CE layer 2 circuit?

VLAN ID must be the same at both ends Signup and view all the answers

What is the advantage of a service provider in Layer 3 VPN?

Service provider’s technical expertise ensures efficient site-to-site routing Signup and view all the answers

What is a characteristic of a Layer 2 VPN?

Customer sites appear to be on the same LAN Signup and view all the answers

What is a requirement for a CE switch in Layer 3 VPN?

The CE switch must be configured to use BGP or OSPF Signup and view all the answers

What is not supported in Layer 2 VPN?

ATM AAL5 encapsulation Signup and view all the answers

What is the advantage of a customer in Layer 2 VPN?

The customer has complete control over policies and routing Signup and view all the answers

What is a characteristic of a service provider in Layer 3 VPN?

The service provider determines the policies and routing Signup and view all the answers

What is not supported in the current implementation of Layer 2 VPN?

ATM AAL5 encapsulation Signup and view all the answers

What is the IP address of the loopback interface on R1?

10.10.10.103 Signup and view all the answers

What is the purpose of the 'mpls label protocol ldp' command?

To specify the LDP protocol for MPLS labels Signup and view all the answers

What is the IP address of the interface fa0/0 on R4?

172.16.0.9 Signup and view all the answers

What is the purpose of the 'xconnect' command?

To configure the Pseudo-wire for the MPLS Layer 2 VPN Signup and view all the answers

What is the IP address of the interface s1/0 on R2?

172.16.0.1 Signup and view all the answers

What is the purpose of the 'mpls ip' command?

To enable MPLS on the router Signup and view all the answers

What is the IP address of the interface fa0/1 on R5?

192.168.2.1 Signup and view all the answers

What is the purpose of the 'mpls ldp router-id' command?

To specify the router ID for the LDP protocol Signup and view all the answers

What happens to the traffic at the receiving site in a Layer 2 VPN?

It is converted back to Layer 2 format Signup and view all the answers

What is the role of the PE switch in a Layer 2 VPN?

To send traffic to the appropriate tunnel Signup and view all the answers

What is the purpose of a Layer 2 circuit?

To provide a point-to-point Layer 2 connection Signup and view all the answers

How many logical interfaces are required for each site in a full-mesh topology?

Two Signup and view all the answers

What is the responsibility of the customer in a Layer 2 VPN?

To configure their own switches to carry all Layer 3 traffic Signup and view all the answers

What is the topology of the VPN determined by?

Policies configured on the PE switches Signup and view all the answers

What is the benefit of a Layer 2 VPN for customers?

They can manage their own traffic Signup and view all the answers

What is the role of the service provider in a Layer 2 VPN?

To detect the amount of traffic to be carried Signup and view all the answers

What is the primary function of the VPN Forwarding Tables (VFTs) in Draft-Kompella?

To populate and maintain the information provisioned for local CEs Signup and view all the answers

What is used for Layer 2 Label Distribution in Draft-Martini?

LDP Signup and view all the answers

What is the purpose of the DLCIs in Draft-Kompella?

To identify remote CE connections Signup and view all the answers

What is a benefit of using MPLS-based Layer 2 VPNs?

It allows customers to maintain control over their network administration Signup and view all the answers

What is distributed by the PEs via MP-iBGP in Draft-Kompella?

VCTs Signup and view all the answers

What is a supported Layer 2 technology in Draft-Kompella?

Ethernet VLAN Signup and view all the answers

How are VCTs received in Draft-Kompella?

Via MP-iBGP Signup and view all the answers

What does the PE device do with the customer's routes in a Layer 2 VPN?

It uses them to populate the VFT Signup and view all the answers

What is the primary difference between a Layer 2 circuit and a circuit cross-connect (CCC)?

A Layer 2 circuit can transport multiple Layer 2 circuits over a single label-switched path (LSP) tunnel. Signup and view all the answers

What is the purpose of the VPN label advertised by the remote PE switch?

To route traffic from the local CE switch to the remote CE switch. Signup and view all the answers

What is the signalling protocol used for advertising VPN labels?

LDP Signup and view all the answers

What is the benefit of using MPLS-based Layer 2 VPNs for service providers?

The same PE router can run Layer 3 VPNs as well as Layer 2 VPNs. Signup and view all the answers

What is the primary benefit of using Layer 2 MPLS VPNs for customers?

Customers can use their existing Layer 2 VPNs over an MPLS backbone. Signup and view all the answers

What is the primary reason why providers are pushed to use two core networks?

ATM is not fast enough to support Internet traffic. Signup and view all the answers

What is the primary advantage of using MPLS-based Layer 2 VPNs?

The same PE router can run Layer 3 VPNs as well as Layer 2 VPNs. Signup and view all the answers

What is the primary function of the PE switch in an MPLS-based Layer 2 VPN?

To forward traffic between the local CE switch and the remote PE switch. Signup and view all the answers

What is a requirement for a PE-CE layer 2 circuit?

Same VLAN ID at both ends Signup and view all the answers

What is not supported in the current implementation of Layer 2 VPN?

Frame Relay encapsulation and ATM AAL5 Signup and view all the answers

What is the primary function of the CE device in a Layer 2 VPN?

Forwarding traffic to the service provider's PE switch Signup and view all the answers

What is an advantage of a Layer 2 VPN for customers?

Customers have complete control over policies and routing Signup and view all the answers

What is the format of traffic forwarded by the CE switch in a Layer 2 VPN?

Layer 2 frames Signup and view all the answers

What is a characteristic of a Layer 2 VPN?

Customer sites appear to be on the same LAN Signup and view all the answers

What is an advantage of a service provider in a Layer 3 VPN?

Service provider does not require information about customer's network topology Signup and view all the answers

What is necessary for CE devices at both ends in a Layer 2 VPN?

Configuration for routing to carry Layer 3 traffic Signup and view all the answers

What is the primary goal of MPLS in terms of Class of Service and Quality of Service?

To address issues related to CoS and QoS Signup and view all the answers

How does the customer edge switch forward traffic in an MPLS-based Layer 2 VPN?

In a Layer 2 format Signup and view all the answers

What is a benefit of using MPLS-based VPNs?

Scalability with traffic-engineering capability Signup and view all the answers

What is the role of the provider edge switch in an MPLS-based Layer 2 VPN?

To receive traffic from the customer edge switch Signup and view all the answers

Which of the following is not a benefit of MPLS-based Layer 2 VPNs?

Support for native ATM, SONET, and Ethernet frames Signup and view all the answers

What is the primary function of MPLS in an MPLS-based Layer 2 VPN?

To forward traffic based on MPLS labels Signup and view all the answers

What is a standard for Layer 2 VPNs?

Draft-Kompella Signup and view all the answers

What is the advantage of using MPLS-based VPNs for customers?

Converged, differentiated classes of services Signup and view all the answers

What is the primary function of the PE switch in a Martini-based Layer 2 VPN?

To distribute a VC label for each Layer 2 circuit defined Signup and view all the answers

What is distributed by the PE switch for each Layer 2 circuit in a Martini-based Layer 2 VPN?

A VC label Signup and view all the answers

What is required for each PE-CE connection at both ends in a Martini-based Layer 2 VPN?

Like circuits Signup and view all the answers

What is used for label distribution in a Martini-based Layer 2 VPN?

LDP Signup and view all the answers

What type of label is used in a Martini-based Layer 2 VPN?

VC label Signup and view all the answers

What is the role of PE-2 in a Martini-based Layer 2 VPN?

To use the received labels as output labels to reach the respective Layer 2 circuit Signup and view all the answers

What is the relationship between BGP and LDP in a Martini-based Layer 2 VPN?

LDP is used for label distribution and BGP is not required Signup and view all the answers

What is the purpose of provisioning the CE in a Martini-based Layer 2 VPN?

To configure Layer 2 circuit IDs one each for remote CE device Signup and view all the answers

What is the purpose of the command 'xconnect 10.10.10.103 1 encapsulation mpls' on R3?

To set up a pseudowire connection for MPLS-based Layer 2 VPN Signup and view all the answers

What is the state of the LDP neighbor 10.10.10.103:0 (2) on R3?

Up Signup and view all the answers

What is the destination IP address of the ping command on R4?

172.16.0.10 Signup and view all the answers

What is the benefit of MPLS VPN for inter-site traffic?

Optimal routing Signup and view all the answers

What is the destination IP address of the ping command on R5?

172.16.0.9 Signup and view all the answers

What is the purpose of the command 'mpls label protocol ldp'?

To establish an LDP neighbor relationship Signup and view all the answers

What is the state of the line protocol on the pseudowire interface on R3?

Up Signup and view all the answers

What is the purpose of the command 'int fa0/0' on R3?

To enter interface configuration mode for FA0/0 Signup and view all the answers

What is the purpose of the 'mpls label protocol ldp' command?

To configure the MPLS label distribution protocol Signup and view all the answers

What is the IP address of the interface fa0/0 on R4?

172.16.0.9 Signup and view all the answers

What is the purpose of the 'xconnect' command?

To configure the Pseudo-wire technology Signup and view all the answers

What is the IP address of the loopback interface on R1?

10.10.10.103 Signup and view all the answers

What is the purpose of the 'mpls ip' command?

To enable MPLS on an interface Signup and view all the answers

What is the IP address of the interface fa0/1 on R5?

192.168.2.1 Signup and view all the answers

What is the purpose of the 'mpls ldp router-id' command?

To specify the LDP router ID Signup and view all the answers

What is the IP address of the interface s1/0 on R2?

172.16.0.1 Signup and view all the answers

What is the primary goal of MPLS in packet-switched networks?

To provide a unified data-carrying service for both circuit-based and packet-switching clients Signup and view all the answers

What is the benefit of using MPLS-based VPNs in terms of Class of Service (CoS) and Quality of Service (QoS)?

It addresses issues related to CoS and QoS Signup and view all the answers

What is the format of traffic forwarded by the customer edge switch in an MPLS-based Layer 2 VPN?

Layer 2 Signup and view all the answers

What is the primary function of the provider edge switch in an MPLS-based Layer 2 VPN?

To receive traffic from the customer edge switch Signup and view all the answers

What is the benefit of using MPLS in terms of Layer 3 header analysis?

It reduces the need for Layer 3 header analysis Signup and view all the answers

What is the primary difference between MPLS-based Layer 2 VPNs and MPLS-based Layer 3 VPNs?

Layer 2 VPNs operate at Layer 2, while Layer 3 VPNs operate at Layer 3 Signup and view all the answers

What is the advantage of using MPLS-based VPNs in terms of scalability?

They can build scalable VPNs with traffic-engineering capability Signup and view all the answers

What is the role of the Internet in the context of MPLS-based VPNs?

It provides converged, differentiated classes of services to users with optimal use of resources Signup and view all the answers

What is the primary function of the Provider Edge (PE) switch in a Layer 2 VPN?

To send data to the appropriate tunnel Signup and view all the answers

What is required for a customer to configure in a Layer 2 VPN?

Their own switches to carry all Layer 3 traffic Signup and view all the answers

What determines the VPN topology in a Layer 2 VPN?

Policies configured on the PE switches Signup and view all the answers

What is the format of traffic sent by the Customer Edge (CE) switch in a Layer 2 VPN?

Layer 2 frames Signup and view all the answers

How many physical links are required to connect each PE switch to each CE router or switch in a full-mesh Layer 2 VPN?

One Signup and view all the answers

What is the role of the service provider in a Layer 2 VPN?

To carry traffic between customer sites Signup and view all the answers

What is a Layer 2 circuit?

A point-to-point Layer 2 connection Signup and view all the answers

What is the responsibility of the customer in a Layer 2 VPN?

To configure their own switches to carry all Layer 3 traffic Signup and view all the answers

On which router is the 'xconnect' command configured?

R1 Signup and view all the answers

What is the purpose of the 'mpls ldp router-id' command?

To specify the router ID for the LDP process Signup and view all the answers

What is the benefit of using MPLS-based Layer 2 VPNs for customers?

All of the above Signup and view all the answers

What is the purpose of the 'mpls ip' command?

To enable MPLS on an interface Signup and view all the answers

Which router has an IP address of 10.10.10.103 configured on its loopback interface?

R1 Signup and view all the answers

What is the purpose of the 'mpls label protocol ldp' command?

To specify the label distribution protocol as LDP Signup and view all the answers

How many logical interfaces are required for each site in a full-mesh topology?

n-1 Signup and view all the answers

What is the primary function of the VPN Forwarding Tables (VFTs) in Draft-Kompella?

To forward traffic based on VPN labels Signup and view all the answers

What is the primary function of the 'xconnect' command in an MPLS-based Layer 2 VPN?

To establish a Layer 2 circuit between the PE and CE devices Signup and view all the answers

What is the benefit of using MPLS-based Layer 2 VPNs for inter-site traffic?

Optimal routing for traffic belonging to the customer Signup and view all the answers

What is the role of the PE device in an MPLS-based Layer 2 VPN?

To forward customer traffic to the correct VPN Signup and view all the answers

What is the purpose of the LDP protocol in an MPLS-based Layer 2 VPN?

To distribute MPLS labels between the PE devices Signup and view all the answers

What is the primary function of a Layer 2 circuit in an MPLS-based Layer 2 VPN?

To establish a connection between the PE and CE devices Signup and view all the answers

What is the advantage of using MPLS-based Layer 2 VPNs for customers?

Optimal routing for traffic belonging to the customer Signup and view all the answers

What is the role of the CE device in an MPLS-based Layer 2 VPN?

To establish a Layer 2 circuit with the PE device Signup and view all the answers

What is the primary function of the VPN forwarding tables in an MPLS-based Layer 2 VPN?

To forward customer traffic to the correct VPN Signup and view all the answers

What is the primary function of the VPN Forwarding Tables (VFTs) in Draft-Kompella?

To populate information provisioned for local CEs Signup and view all the answers

What is the primary function of the PE switch in a Layer 2 VPN?

To send traffic across the service provider's network Signup and view all the answers

Which of the following is NOT a supported Layer 2 technology in Draft-Kompella?

IP over ATM Signup and view all the answers

What is the purpose of distributing VCTs in Draft-Kompella?

To auto-discover VPN members Signup and view all the answers

What is the format of traffic that is sent by the PE switch across the service provider's network?

MPLS format Signup and view all the answers

What is the primary benefit of Layer 2 MPLS VPNs for customers?

Scalability and flexibility Signup and view all the answers

What is the benefit of a Layer 2 VPN for customers?

It allows customers to know which VPN interfaces connect to which of their own sites Signup and view all the answers

How are VCTs distributed in Draft-Kompella?

Using MP-iBGP Signup and view all the answers

What determines the VPN topology in a Layer 2 VPN?

Policies configured on the PE switches Signup and view all the answers

What is the purpose of the DLCIs in Draft-Kompella?

To identify VPN circuits Signup and view all the answers

What is required to connect each PE switch to each CE router or switch in a full-mesh Layer 2 VPN?

One physical link Signup and view all the answers

What is the role of the customer edge switch in a Layer 2 VPN?

To select the appropriate circuit to send traffic Signup and view all the answers

What is the main difference between Draft-Kompella and Draft-Martini?

Label distribution protocol used Signup and view all the answers

How does the PE device map the circuit ID to an MPLS LSP in a Layer 2 VPN?

Using LDP Signup and view all the answers

What is a Layer 2 circuit?

A point-to-point Layer 2 connection Signup and view all the answers

What is the responsibility of the service provider in a Layer 2 VPN?

To carry traffic between the customer's sites Signup and view all the answers

In a Layer 2 VPN, what is required for a PE-CE layer 2 circuit?

Same VLAN ID at both ends Signup and view all the answers

What is not supported in the current implementation of Layer 2 VPN?

Frame Relay and ATM AAL5 encapsulations Signup and view all the answers

What is the role of the service provider in a Layer 3 VPN?

Determines the policies and routing Signup and view all the answers

What is the benefit of a Layer 2 VPN for customers?

Customer has complete control over policies and routing Signup and view all the answers

How does the CE switch forward traffic in a Layer 2 VPN?

In Layer 2 format to the service provider's PE switch Signup and view all the answers

What is the primary benefit of a Layer 3 VPN for service providers?

Service providers can provide additional value-added services Signup and view all the answers

What is required for the CE switch in a Layer 3 VPN?

Configuration for routing to carry Layer 3 traffic Signup and view all the answers

What is the primary difference between Layer 2 VPN and Layer 3 VPN?

Layer 2 VPN requires customer's network topology, while Layer 3 VPN does not Signup and view all the answers

Study Notes

MPLS-Based Layer 2 VPNs

MPLS (Multi-Protocol Label Switching) is a data-carrying mechanism that operates between Layer 2 (data link layer) and Layer 3 (network layer or IP Layer), also referred to as a "Layer 2.5" protocol.
MPLS provides a unified data-carrying service for both circuit-based clients and packet-switching clients, offering a datagram service model.
MPLS can carry various types of traffic, including IP packets, native ATM, SONET, and Ethernet frames.

MPLS-Layer 2 VPN

In an MPLS-based Layer 2 VPN, traffic is forwarded by the customer's CE (customer edge) switch or router to the service provider's PE (provider edge) switch in a Layer 2 format.
The traffic is carried by MPLS over the service provider's network and then converted back to Layer 2 format at the receiving site.
Routing occurs on the customer's switches, typically on the CE switch.

Layer 2 Circuits

A Layer 2 circuit is a point-to-point Layer 2 connection that uses MPLS or another tunneling technology on the service provider's network.
In Layer 2 VPNs, customers maintain control over most of the administration of their networks, including own routing policies.

Layer 2 VPN Standards

Two proposals for MPLS-based Layer 2 VPNs: Draft-Kompella and Draft-Martini.
Draft-Kompella uses MP-iBGP for Layer 2 VPN label distribution, while Draft-Martini uses LDP for Layer 2 Label Distribution.

Draft-Kompella

Uses VPN Forwarding Tables (VFTs) and VPN Connection Tables (VCTs) to distribute labels and configure VPN topologies.
VFTs are populated with information provisioned for the local CE, including circuit ID, inner label, and outer label.
VCTs are received from other PEs via MP-iBGP and are used to configure VPN topologies.

Draft-Martini

Uses LDP for signalling in the provider's network.
VLAN ID must be the same at both ends (PE-CE layer 2 circuit).
Frame Relay and ATM AAL5 encapsulations are not supported.
CE devices at both ends should be configured for routing to carry Layer 3 traffic.

Comparison between MPLS-Based Layer 2 VPN and Layer 3 VPN

Layer 2 VPN: customer sites appear to be on the same LAN, even if geographically dispersed; customer has complete control over policies and routing.
Layer 3 VPN: service provider determines policies and routing; customer must share information about their network topology.### Configuration of MPLS Layer 2 VPN using Ethernet as Layer 2 Transport
Configuration on customer routers R4 and R5 involves setting up IP addresses and RIP version 2 on interfaces fa0/0 and fa0/1.
R4 and R5 have IP addresses 172.16.0.9 and 172.16.0.10 respectively on interface fa0/0, and 192.168.1.1 and 192.168.2.1 respectively on interface fa0/1.
RIP version 2 is enabled with networks 192.168.1.0 and 172.16.0.8 on R4, and networks 192.168.2.0 and 172.16.0.8 on R5.

Configuration on ISP Routers R1, R2, and R3

R1, R2, and R3 are configured with IP addresses on loopback 0 (10.10.10.103, 10.10.10.104, and 10.10.10.105 respectively), and on serial interfaces s1/0 (172.16.0.2, 172.16.0.1, and 172.16.1.2 respectively).
OSPF is enabled with area 0 on all three routers.
MPLS is enabled with label protocol LDP on all three routers.
MPLS label ranges are set to 100-199 on R1, 200-299 on R2, and 300-399 on R3.

Configuration of MPLS Layer 2 VPN Virtual Circuit using Pseudo-wire Technology

On router R1, a virtual circuit is set up using xconnect with the peer 10.10.10.105 and encapsulation MPLS.
The pseudowire interface is brought up, and the configuration is saved.

MPLS-Based Layer 2 VPNs

A Layer 2 circuit is similar to a circuit cross-connect (CCC), but multiple Layer 2 circuits can be transported over a single label-switched path (LSP) tunnel between two provider edge (PE) switches.
In contrast, each CCC requires a dedicated LSP.
Junos OS implementation of Layer 2 circuits only supports remote forms of Layer 2 circuits, i.e., connections from a local customer edge (CE) switch to a remote CE switch.
Packets are sent to the remote CE switch using an egress VPN label advertised by the remote PE switch, which transits over an RSVP or LDP LSP tunnel to the remote PE switch connected to the remote CE switch.
LDP is the signalling protocol used for advertising VPN labels.

Layer 2 Provider-Provisioned VPNs

Providers used to use a single ATM core to support Internet and VPN traffic, but ATM is not fast enough to support Internet traffic.
Providers are pushed to have two core networks, but why not support both over an MPLS core?
Map Frame Relay and ATM to MPLS LSPs, as L3 VPNs can also be over the same core.

Benefits of Layer 2 MPLS

Service providers do not have to invest in separate Layer 2 devices to provide Layer 2 VPN service.
The same PE router can run Layer 3 VPNs as well as Layer 2 VPNs.
A Layer 2 MPLS VPN allows customers to use their existing Layer 2 VPN service over an MPLS backbone.

MPLS-Based Layer 2 VPN Configuration

Learning objectives include understanding MPLS L2 VPN, provider provisioned VPN, benefits of Layer 2 VPN, standards for Layer 2 VPN, comparison between MPLS L2 & L3 VPN, and MPLS-based VPN configuration.

Introduction to MPLS

Multi Protocol Label Switching (MPLS) is a data-carrying mechanism in packet-switched networks that operates at a TCP/IP layer considered to be between traditional definitions of Layer 2 (data link layer) and Layer 3 (network layer or IP Layer), and thus is often referred to as a "Layer 2.5" protocol.
MPLS was designed to provide a unified data-carrying service for both circuit-based clients and packet-switching clients, which provide a datagram service model.
MPLS can be used to carry many different kinds of traffic, including IP packets, as well as native ATM, SONET, and Ethernet frames.

MPLS-Layer 2 VPN

In an MPLS-based Layer 2 VPN, traffic is forwarded by the customer's CE switch to the service provider's PE switch in a Layer 2 format.
It is carried by MPLS over the service provider's network and then converted back to Layer 2 format at the receiving site.
On a Layer 2 VPN, routing occurs on the customer's switches, typically on the CE switch.

Layer 2 Circuits

A Layer 2 circuit is a point-to-point Layer 2 connection that uses MPLS or another tunneling technology on the service provider's network.
VLAN ID must be the same at both ends (PE-CE Layer 2 circuit).
Frame Relay & ATM AAL5 encapsulations are not supported at present.
CE devices at both ends should be configured for routing to carry Layer 3 traffic.

Comparison between MPLS-Based Layer 2 VPN & Layer 3 VPN

In a Layer 2 VPN, the customer has complete control over policies and routing, while in a Layer 3 VPN, the service provider determines the policies and routing.
In a Layer 2 VPN, the CE switch forwards traffic to the service provider's PE switch in a Layer 2 format, while in a Layer 3 VPN, the customer's CE switch must be configured to use BGP or OSPF to communicate with the service provider's PE switch to carry IP prefixes across the network.

Layer 2 VPN Standards

There are two proposals for MPLS-based Layer 2 VPNs: Draft-Kompella (uses MP-iBGP for Layer 2 VPN label distribution) and Draft-Martini (uses LDP for Layer 2 Label Distribution).

Draft-Kompella and Draft-Martini Overview

Draft-Kompella uses MP-iBGP for label distribution and has VPN Forwarding Tables (VFTs) and VPN Connection Tables (VCTs).
Draft-Martini uses LDP for signalling in the provider's network and supports Frame Relay, ATM AAL5 CPCS Mode, ATM Transparent Cell Mode, Ethernet, Ethernet VLAN, Cisco HDLC, and PPP.

MPLS-Based Layer 2 VPNs

Learning Objectives

Understand MPLS L2 VPN
Understand provider-provisioned VPN
Know the benefits of Layer 2 VPN
Understand the standards for Layer 2 VPN
Compare MPLS L2 VPN with L3 VPN
Configure MPLS-based VPN

Introduction to MPLS

MPLS is a data-carrying mechanism in packet-switched networks
It operates at a TCP/IP layer between traditional definitions of Layer 2 and Layer 3
MPLS is often referred to as a "Layer 2.5" protocol
It provides a unified data-carrying service for both circuit-based and packet-switching clients
MPLS can carry many different kinds of traffic, including IP packets, ATM, SONET, and Ethernet frames

MPLS-Layer 2 VPN

In an MPLS-based Layer 2 VPN, traffic is forwarded by the customer's CE switch to the service provider's PE switch in a Layer 2 format
Traffic is carried by MPLS over the service provider's network and then converted back to Layer 2 format at the receiving site
Routing occurs on the customer's switches, typically on the CE switch
The CE switch must select the appropriate circuit on which to send traffic

Layer 2 Circuits

A Layer 2 circuit is a point-to-point Layer 2 connection that uses MPLS or another tunneling technology on the service provider's network
Since LDP is used, BGP is not required
Only like circuits are allowed between PE-CE at both ends
Inner label is defined as Virtual Circuit Label (VC Label)
Martini-VC Label Distribution is used to distribute VC labels for each Layer 2 circuit

Configuration of MPLS Layer 2 VPN

Configure Layer 2 circuit IDs one each for remote CE device
Configuration involves setting up IP addresses, routing, and MPLS on the routers

Configuration of MPLS Layer 2 VPN using Ethernet as Layer 2 Transport

Configuration involves setting up IP addresses, routing, and MPLS on the routers
Routers R4, R5, R1, R2, and R3 are configured with IP addresses, routing, and MPLS

Configuration of MPLS Layer 2 VPN Virtual Circuit using Pseudo-wire Technology

Configuration involves setting up xconnect on the routers
On Router R1, xconnect is configured to connect to Router R3
On Router R3, xconnect is configured to connect to Router R1

Observations

Ping tests are successful between routers R4, R5, and R1, R2, and R3

Conclusion

MPLS VPN provides optimal routing for traffic belonging to the customer for inter-site traffic

MPLS-Based Layer 2 VPNs

MPLS VPN provides optimal routing for inter-site traffic.
Configuration of MPLS Layer 2 VPN using Ethernet as Layer 2 transport:
- On customer routers R4 and R5:
  - Configure IP addresses and routing information.
  - Enable RIP and configure network commands.
- On ISP routers R1, R2, and R3:
  - Configure IP addresses, OSPF routing, and MPLS labels.
  - Enable CEF and MPLS IP.

Configuration of MPLS Layer 2 VPN Virtual Circuit using Pseudo-wire Technology

On Router R1:
- Configure xconnect command to establish a pseudo-wire connection to Router R3.
On Router R3:
- Configure xconnect command to establish a pseudo-wire connection to Router R1.

MPLS Layer 2 VPN Overview

In a Layer 2 VPN, routing occurs on the customer's switches.
The customer's CE switch selects the appropriate circuit to send traffic.
The PE switch sends traffic across the service provider's network to the PE switch connected to the receiving site.
The service provider must detect the amount of traffic the Layer 2 VPN will carry.

Layer 2 Circuits

A Layer 2 circuit is a point-to-point Layer 2 connection that uses MPLS or another tunneling technology on the service provider's network.
In Layer 2 VPNs, customers can maintain control over most of their network administration.

Layer 2 VPN Standards

Two proposals for MPLS-based Layer 2 VPNs: Draft-Kompella and Draft-Martini.
Draft-Kompella uses MP-iBGP for Layer 2 VPN label distribution.
Draft-Martini uses LDP for Layer 2 label distribution.

Draft-Kompella

Uses VPN Forwarding Tables (VFTs) and VPN Connection Tables (VCTs).
VFTs are populated with CE information and VCTs are distributed to PEs via MP-iBGP.
Provisioning customer site on PE involves configuring DLCIs and VFTs.

Draft-Kompella Data Flow

Packet flow involves IGP label, site label, and DLCI lookup.

Draft-Kompella Supported Layer 2 Technologies

Frame Relay
ATM AAL5 CPCS mode
ATM Transparent Cell mode
Ethernet
Ethernet VLAN
Cisco HDLC
PPP### MPLS-Based Layer 2 VPN Requirements
VLAN ID must be the same at both ends of the PE-CE layer 2 circuit
CE devices at both ends must be configured for routing to carry layer 3 traffic
Frame Relay and ATM AAL5 encapsulations are not supported

Comparison of MPLS-Based Layer 2 VPN and Layer 3 VPN

Layer 2 VPN

Customer sites appear to be on the same LAN, even if geographically dispersed
Customer has complete control over policies and routing
CE switch forwards traffic to the service provider's PE switch in Layer 2 format

Layer 3 VPN

Service provider's technical expertise ensures efficient site-to-site routing
Service providers can provide additional value-added services through network convergence that encompasses voice, video, and data
Service provider determines policies and routing
Customer's CE switch must be configured to use BGP or OSPF to communicate with the service provider's PE switch to carry IP prefixes across the network

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Description

Learn about MPLS-based Layer 2 VPNs, provider provisioned VPN, benefits, standards, and configuration. Compare MPLS L2 and L3 VPN and understand MPLS based VPN Configuration.