Monday, July 25, 2011

MPLS vs Ethernet WAN

Actually MPLS is a form of Ethernet WAN.

Ethernet just refers to the type of handoff. In this case, the provider is giving you a direct Ethernet handoff that can plug straight into your data network without further conversion. This would be compared to something like a T1 handoff that would need to be converted to Ethernet via hardware device or router NIC.

MPLS is a carrier managed service where you can request that specific traffic, be it based on IP or TCP port, can be given precedence over other types of traffic. This management is end-to-end, meaning that all of the carrier's routers and switches will maintain the integrity of QoS settings.

An Ethernet WAN is typically a VPN for city to city or possibly a simple point-to-point fiber connection in the case of building to build connectivity. The sort of connection operates at layer 2 only where you provide the IP addressing. With this type of connection the carrier has no perception into the traffic and therefore there is not QoS. This is typically the cheaper of the two.

I thought I’d post up some content on VPLS (Layer 2 VPN) and MPLS (Layer 3 VPN) as I’ve been asked recently about why an IT Manager would select one over the other. It was a client who had been told by the telco that provisioning layer 2 and layer 3 VPN’s would provide resiliency which isn't the case.

First it’s good to clear up that VPLS is actually an evolution of MPLS rather then a separate technology. MPLS (Multi Protocol Label Switching) is a protocol used for traffic engineering and performance increases across routed networks. So, if you think about a packet (data) traversing a providers network, pre-MPLS, the intermediate routers along the way would in the olden days (!) have to look up the destination of that packet and route it accordingly which added time (latency).

So, MPLS works on a concept called labels hence it’s name - so rather than the router having to perform a lookup at every point along the way, pre-determined paths are provisioned meaning that a packet follows a “label switched path” through the network increasing performance.

VPLS (Virtual Private LAN Service) is now being offered by carriers as a method of extending LAN connectivity to each of your sites at layer 2. So, essentially you’re provided with Ethernet handoff at each of your sites effectively providing you with LAN connectivity. True VPLS is provided as any to any connectivity in the same way as a layer 3 private “MPLS” VPN. At any rate, VPLS is provided over a providers core MPLS network hence why it does not, as standard, offer resiliency.

So, why would you as an IT Manager or IT Director select one or the other? Well, the strong differentiator is the Layer 2 and Layer 3 difference on the OSI model. At layer 2, you have much more control of your network. So, if for example you have a legacy protocol which needs to be transported between your sites, a Layer 2 VPN allows you to control layer 3. These protocols may not be not be supported by a providers layer 3 MPLS VPN as standard which may force you down the VPLS route. At Layer 2, the network performs like the LAN so you have that layer 2 control. If you manage your own routers and CPE, a layer 2 VPN is also a good option since, again, you’re in control of the layer 3 routed element and can deal with requirements at layer 3 as they arise.

It is possible to mix and match - you could for example interconnect hosting sites via layer 2 and all other branch sites via layer 3.

For more information and free assistance to help you decide what the right solution would be for your business network .... take advantage of the no cost support available here: MPLS and Business Ethernet

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Anonymous Anonymous said...

Hi, can you explain why an ethernet carrier would have "no perception into the traffic and therefore there is not QoS"? Wouldn't diffserv and/or cos markings be observed? Thanks.

3:43 PM  

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