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Transports for MPLS

I'm really confused about where MPLS sits in the network stack

We have Frame Relay over T1s and are migrating to MPLS, but the MPLS service going to be delivered over Frame Relay.

I don't understand this because I keep reading about how MPLS has all but usurped Frame Relay. Why is it being sold to us with Frame Relay as the L2 protocol?

Could MPLS be deleviered without Frame Relay? Can it completely take the place of an L2 protocol or does it need to run over Frame, HDLC, PPP or something like that?

This gets even more confusing with pseudowires where you can actually transport HDLC over MPLS!? What is MPLS running over in the first place?

Sorry if this question is hard to follow let me know if you need me to clarify anything- its difficult to write a question about something that is so confusing to me.

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Cisco Employee

Re: Transports for MPLS

I am not recommending that you actually do Ethernet over T1. I was just pointing out that it is possible.

Again, there is no MPLS between the CE and the PE, so even though you had Ethernet, it would not be MPLS over Ethernet.

Regards

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
9 REPLIES

Re:Transports for MPLS

Hello
Your isp would most probably install a mpls circut at your site and you would attach to this .via a fasterhernet port on your wan router which would make it a ce router which intern would connect to your isp router where mpls will be situated.

All the mpls config is usually invisible to the client

Res
Paul

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Cisco Employee

Transports for MPLS

Hi,

MPLS is generally described as a layer 2.5 protocol as it gets inserted between the layer 2 and the layer 3. So you can in principle run MPLS over any layer 2 protocol, although it is not very common to see MPLS being run over Frame Relay.

Regards

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
New Member

Re: Transports for MPLS

So I still don't really get it though. Does MPLS HAVE to run over an L2 protocol or can it be used without one? If mpls does require an L2 protocol what is the most common one used to deliver it?

"... install mpls circut at your site ..." - this sounds like a physical layer thing. We have T1 lines so is there a special mpls T1 device?

Also, what advantages are there for a service provider to sell MPLS over frame?

And thanks for the replies. Still trying to figure this out.

Cisco Employee

Re: Transports for MPLS

MPLS does indeed need a layer 2 to run over. It is most common to see service providers use Ethernet these days.

In your case, as you are the customer and not involved in the MPLS network as such, your service provider probably uses Frame Relay as an access into the MPLS network rather than running MPLS over FR.

Regards

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
New Member

Re: Transports for MPLS

Thanks for the reply.

"your service provider probably uses Frame Relay as an access into the MPLS network rather than running MPLS over FR"- you mean access into their own MPLS cloud right? I still don't get why they would do that.

Is it because we already have T1 lines that frame runs on top of? Is it because you can't deliver MPLS directly over a T1 so their using frame?

So if we wanted to get MPLS over Ethernet that would mean all of those T1 smartjack cards would have to be ripped out and replaced by something else right? Or can you run Ethernet traffic over a T1 line?

Sorry for all the questions I appreicent the help.

Cisco Employee

Re: Transports for MPLS

Yes, I meant access into their own MPLS network. In other words, FR between the CE nd the PE.

The reason your SP keeps the access as FR might be to provide multiplexing of multiple VRF over a T1 link. With Ethernet, they normally use dot1q to do the same but there is no way to multiplex over a T1 unless you run FR or GRE tunnels.

If you wanted to have Ethernet as the access into the MPLS cloud, you would need to replace the T1s indeed. Unless you used some devices to bridge Ethernet traffic over T1.

Regards

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
New Member

Re: Transports for MPLS

Cool thanks for explanations it is much clearer now.

I googled around and found these rather expensive Ethernet over T1 converters. Can you use one of those converters to pass Ethernet traffic over a T1 line- ie have MPLS over ethernet, but with a T1?

Gold

Re: Transports for MPLS

i wouldn't convert Ethernet to serial.

If you are the Customer Edge to an MPLS network, it won't matter.

Generally, the provider will decide what type of transport services are needed.

Cisco Employee

Re: Transports for MPLS

I am not recommending that you actually do Ethernet over T1. I was just pointing out that it is possible.

Again, there is no MPLS between the CE and the PE, so even though you had Ethernet, it would not be MPLS over Ethernet.

Regards

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
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