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Concepts, Configuration & Troubleshooting Layer 2 MPLS VPN Any Transport over MPLS (AToM)

Read the bioWith Vignesh R. P.

Welcome to the Cisco Support Community Ask the Expert conversation.This is an opportunity to learn and ask questions about  concept, configuration and troubleshooting Layer 2 MPLS VPN - Any Transport over MPLS (AToM) with Vignesh R. P.

 

Cisco Any Transport over MPLS (AToM) is a solution for transporting Layer 2 packets over an MPLS backbone. It enables Service Providers to supply connectivity between customer sites with existing data link layer (Layer 2) networks via a single, integrated, packet-based network infrastructure: a Cisco MPLS network. Instead of using separate networks with network management environments, service providers can deliver Layer 2 connections over an MPLS backbone. AToM provides a common framework to encapsulate and transport supported Layer 2 traffic types over an MPLS network core.

Vignesh R. P. is a customer support engineer in the Cisco High Touch Technical Support center in Bangalore, India, supporting Cisco's major service provider customers in routing and MPLS technologies. His areas of expertise include routing, switching, and MPLS. Previously at Cisco he worked as a network consulting engineer for enterprise customers. He has been in the networking industry for 8 years and holds CCIE certification in the Routing & Switching and Service Provider tracks.

 

Remember to use the rating system to let Vignesh know if you have received an adequate response. 

Vignesh might not be able to answer each question due to the volume expected during this event. Remember that you can continue the conversation on the  Service Provider sub-community discussion forum shortly after the event. This event lasts through through September 21, 2012. Visit this forum often to view responses to your questions and the questions of other community members.

 

Hi,

 

I have a question, is MPLS used only in WAN ?

 

My other question is that L2 is basically a Switch but in Switches,their are frames ,how is it that packets are being used?

 

Thanks

 

Hi Fahad,

 

For the first question of your's, no MPLS is not used only in a WAN clound. It can be used in a campus as well as in a LAN environment.

 

For the next question of your's kindly read through the below explanation.

 

Any Transport over Multiprotocol Label Switching (AToM) is the Cisco solution for transporting Layer 2 frames over a Multiprotocol Label Switching (MPLS) backbone.AToM extends the usability of IP networks by enabling the transport of

Layer 2 frames over an MPLS backbone.

 

AToM uses a directed Label Distribution Protocol (LDP) session between edge routers for setting up and maintaining connections. Forwarding occurs through the use of two level labels, switching between the edge routers. The external label (tunnel label), routes the packet over the MPLS backbone to the egress Provider Edge (PE) at the ingress PE. The VC label determines the egress interface, and it binds the Layer 2 egress interface to the tunnel label.

 

AToM accommodates many types of Layer 2 packets, including ATM, Ethernet, Frame Relay, PPP, or High-Level Data Link Control (HDLC)- based networks across multiple Cisco router/switch platforms.

 

Packet is a L3 PDU and frame is a L2 PDU.Technically there is nothing called as Layer 2 packet.A lot of times the term Layer 2 Packets & Layers 2 Frames are being interchanged in usage in case of L2 MPLS VPN.

 

Hope this gives you a lot of clarity. Kindly revrt incase of further assistance.

 

Thanks & Regards,

 

Vignesh R P.

 

Hello Vingesh,

 

I dont agree with you why MPLS can be run on a LAN environment?  This is not documented any where and is not technology known to be run on a LAN environment.!!!  Surely, I would appreciate if you could just give me an example in which LAN environment we can run MPLS, and for what purpose and benefit?

 

 

Regards,

Mohamed

 

TRUE

VLAN 1

Interface: VLAN 1

IP Address Type: Static

IP Address: 172.26.0.192

Mask: 255.255.0.0

Status: Valid

 

VLAN 2

 

Interface: VLAN 2

IP Address Type: Static

IP Address: 172.27.0.1

Mask: 255.255.0.0

Status: Valid

 

 

The default gateway is 172.26.0.252.

 

Hi,

 

Let me rephrase my response on the LAN support here. What I meant to say is as below,

 

MPLS is not a technology meant just to be enabled on WAN interfaces/circuit (which normally is the connection between remote sites or between customer and provider site) but also between point to point connections (Ethernet) within the same customer site.

 

To brief it further, MPLS is normally enabled in between a set of L3 devices (acting as core) within the same customer site which can inturn help in providing services like L2VPN or L3VPN for sites connecting to this core.

Hope this clarifies.

 

The below link can give a good insight on basic MPLS technology.

http://www.cisco.com/en/US/docs/ios/12_0st/12_0st21/feature/guide/fs_rtr.html


This thread is meant for discussion related to AToM - L2VPN. And I would like to remain within that scope for the sheer reason of not diluting this thread.

 

Thanks a lot for understanding.

 

Vingesh,

 

You made a valid describtion now, and your link confirms its a WAN technology used in a Service Provider Network if you go through the link you have provided.

 

Even in the Customer Enterprise Network, as you illustrated,  its used as a WAN, so the term LAN is misconceptual and misleading term here. May be just as you mentioned, you meant different thing.

 

In any way, thanks for your participation and reply, enjoy Your thread!!!

 

 

Regards,

Mohamed

 

Hi,

 

before I ask the question, let me warn you that I'm familiar only with basic MPLS concepts. Could you please explain the difference between AToM and pseudowire? I will also appreciate if you can mention any other competing technology that is achieving same thing.

 

Regards,

Tenaro

 

Hi Tenaro,

 

AToM stands for Any Transport over MPLS and it is Cisco's terminology used for Layer 2 MPLS VPN or Virtual Private Wire Service. It is basically a Layer 2 Point-to-Point Service. AToM basically supports various Layer 2 protocols like Ethernet, HDLC, PPP, ATM and Frame Relay.

 

The customer routers interconnect with the service provider routers at Layer 2. AToM eliminates the need for the legacy network from the service provider carrying these kinds of traffic and integrates this service into the MPLS network that already transports the MPLS VPN traffic.

 

AToM is an open standards-based architecture that uses the label switching architecture of MPLS and can be integrated into any network that is running MPLS. The advantage to the customer is that they do not need to change anything. Their routers that are connecting to the service provider routers can still use the same Layer 2 encapsulation type as before and do not need to run an IP routing protocol to the provider edge routers as in the MPLS VPN solution.


The service provider does not need to change anything on the provider (P) routers in the core of the MPLS network. The intelligence to support AToM sits entirely on the PE routers. The core label switching routers (LSRs) only switch labeled packets, whereas the edge LSRs impose and dispose of labels on the Layer 2 frames.

 

 

Whereas pseudowire is a connection between the PE routers and emulates a wire that is carrying Layer 2 frames. Pseudowires use tunneling. The Layer 2 frames are encapsulated into a labeled (MPLS) packet. The result is that the specific Layer 2 service—its operation and characteristics—is emulated across a Packet Switched Network.

 

 

Another technology that more or less achieves the result of AToM is L2TPV3. In the case of L2TPV3 Layer 2 frames are encapsulated into an IP packet instead of a labelled MPLS packet.

 

Hope the above explanation helps you. Kindly revert incase of further clarification required.

 

Thanks & Regards,

 

Vignesh R P

 

Thank you for your detailed answer. It is becoming more and more clear. I think I'm still not sure if AToM and pseudowire are two competing technologies or pseudowire is just a subset of the AToM. Can Service Provider offer to the customer Layer 2 connectivity between branch offices using AToM feature/technology without implementing pseudowire?

 

Hi Tenaro,

 

Pseudowire is indeed a mandatory subset of AToM and is definitely not a competing technology. And kindly keep in mind that AToM is Layer 2 Point-to-Point service.

 

Thanks & Regards,

 

Vignesh R P

 

hi i m fron cote divoire i do speake french but a little bit of english a got a projet,i have to configure a vpn connection between guinee (conakry) and cote divoire (abidjan) please can u show de command i have to type ?thanks

 

Hi Dagnogo,

 

Nice to hear from you.

 

Kindly confirm if you are looking at a Layer 2 MPLS VPN (Point-to-Point) solution for this project. If yes, then kindly provide me the type of layer 2 connectivity used between the Customer Edge & the Provider Edge at both guinee (conakry) and cote divoire (abidjan) ends for me to assist you further.

 

Thanks & Regards,

 

Vignesh R P

 

Thanks again. Is it OK then to conclude that terms pseudowire and AToM can be used interchangeably?

 

To move this one step further, if we suppose that customer has hub&spoke topology (HQ is the hub, many branch offices can communicate only via HQ), is there any benefit of using clasic L3 VPN MPLS if pseudowire/AToM technology is available? Eliminating any routing protocol between CE and PE equipment is a big plus for pseudowire and I don't see any reason to use MPLS VPN, except maybe with partial mesh topologies...

 

Hi Tenaro,

 

I dont think it would be completely right to conclude that the terms pseudowire & AToM are interchangeable. The Layer 2 MPLS VPN service is called as AToM whereas a pseudowire is the virtual circuit created between the two PEs without which offering AToM service is not possible.

 

Coming to the second part of your question, it is purely based on the customer needs & design on which we can choose between a L2 MPLS VPN solution or L3 MPLS VPN solution. There is no clear distinct winner between them. But generally the below three points are considered to be a plus for L3 MPLS VPN over to L2 MPLS VPN.

 

1) The CE device need not hold on to a huge amount of routing information, thereby helping the CPU on the device.

2) It is a more scalable solution.

3) Finally it makes any-to-any site connectivity possible.


I would like to stress one more time that we cannot conclude if L2 MPLS VPN is better than L3 MPLS VPN or if L3 MPLS VPN is better than L2 MPLS VPN as it is purely based on customer needs and design as mentioned earlier that we choose between them.

 

Thanks & Regards,

 

Vignesh R P

 

Hi Tenaro,

 

I dont think it would be completely right to conclude that the terms pseudowire & AToM are interchangeable. The Layer 2 MPLS VPN service is called as AToM whereas a pseudowire is the virtual circuit created between the two PEs without which offering AToM service is not possible.

 

Coming to the second part of your question, it is purely based on the customer needs & design on which we can choose between a L2 MPLS VPN solution or L3 MPLS VPN solution. There is no clear distinct winner between them. But generally the below three points are considered to be a plus for L3 MPLS VPN over to L2 MPLS VPN.

 

1) The CE device need not hold on to a huge amount of routing information, thereby helping the CPU on the device.

2) It is a more scalable solution.

3) Finally it makes any-to-any site connectivity possible.


I would like to stress one more time that we cannot conclude if L2 MPLS VPN is better than L3 MPLS VPN or if L3 MPLS VPN is better than L2 MPLS VPN as it is purely based on customer needs and design as mentioned earlier that we choose between them.

 

Thanks & Regards,

 

Vignesh R P

 

This document was generated from the following discussion: Ask the Expert:Concepts, Configuration and Troubleshooting Layer 2 MPLS VPN – Any Transport over MPLS (AToM)

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