Today let’s only consider Ethernet based WAN technologies and review what they are, how they are delivered, and which services will best meet your needs as an enterprise customer. For the purposes of this discussion, we’ll be defining “Ethernet WAN services” as services that are presented to you as Ethernet at each end of the transport. This doesn’t mean Ethernet on your LAN side of your router or CPE (pretty much every connectivity type is going to present that way), but Ethernet on the WAN side of your router.
These types of connections are often sought out by enterprise customers because they can be used to virtually “extend” the local LAN from one office to another. In some cases it’s possible to extend your local broadcast domain and local IP subnets across these links, so that your remote offices look just like they are on the local LAN. For years these services have been popular in metro areas (fairly short reach), but today Metro Ethernet (or Carrier Ethernet) services are available stretching around the globe. Most enterprise network shops are equipped with staffers that understand and work with Ethernet every day. It stands to reason then, that if we deliver the WAN service as Ethernet, that makes connecting to your remote offices easier to understand for your existing staff, and therefore faster and cheaper to implement.
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The Metro Ethernet Forum started in around 2001 with the aim of creating a set of standards and services that would define how carriers delivered Ethernet services to customer’s doorsteps over a global set of dissimilar technologies.
They have worked hard to ensure that providers such as BT Wholesales Carrier products and others around the world over can implement Ethernet consistently, and deploy a standardised set of services. They also work to ensure that these carriers can ensure scalability, reliability, Quality of Service, and provide a reasonable level of service management.
There are 3 basic services that are deployed by BT Wholesale (with some variance in HOW they are deployed). E-Line services are a point-to-point virtual Ethernet wire that allows an Ethernet port at location (a) to talk to an Ethernet port at location (b). E-LAN services are multipoint to multipoint services that allow the provider’s network to act something like a large Ethernet switch connecting your branch offices. Finally, E-tree services are something of a hybrid between the previous two. In an E-Tree scenario, your provider’s network can connect multiple points, but configure things so that not every site can talk to every other site. This is often referred to as a “root” and “leaf” setup where the “leaves” can all talk to the “root” site, but they cannot talk to one another without going through the “root”.
While the delivery at your doorstep is Ethernet, the BT Wholesale may use a number of underlying technologies to deliver the frames throughout their global backbone. I’ll give you some examples here, but they are not all inclusive. For short, metro or regional deployments the provider may actually be using native Ethernet gear with underlying fibre optic gear (CWDM or DWDM). For longer distances, some providers may be deploying the carrier Ethernet service over an SDH/SONET network. Other providers might choose to use their global IP/MPLS backbone to deploy the carrier Ethernet service of your choice. The Metro Ethernet Forum’s standards help to ensure that even if your global deployment spans three or four providers, the services will be deployed uniformly and predictably across borders and across mediums.
Without diving too deeply into how BT delivers carrier Ethernet services, there are some things you should know about how this technology is delivered, and what that delivery means to your enterprise.
In a Wholesale Carrier Ethernet environment, the provider equipment is often acting as the “global switch” bridging your Ethernet devices together. In fact, that equipment may be acting as the “global switch for hundreds, or thousands of enterprises worldwide. While these switching tables (mac learning tables) are secure, and kept separate from one another, the provider may need to impose limits on how many mac addresses it can “learn” from your Ethernet environment in an E-LAN setup. There may also be limits to how you can deploy your own VLANs across the Provider’s Ethernet services (these limits will depend largely on which of the 3 basic services you choose from above). In some scenarios you can use all 4096 possible VLANs, in some scenarios, you may be limited to a single VLAN.
Another important consideration is understanding what the Carrier Ethernet service is going to do with your Layer 2 control protocols (CDP, Spanning Tree Protocol, Pause frames, LACP, BPDUs, RTSP, etc). Depending on which of the 3 basic services you choose, the L2CP frames can be discarded, manipulated, or passed straight through the provider network transparently. To try to break down what will happen to your L2CP frames in any given scenario is beyond the scope of this article, but it’s important to know that the behaviour will be different than it would be on your local LAN. So do your best to identify what low level protocols like these are important to the function of your critical applications, and remember to talk with your provider about the services you’re intending to purchase. You need to know how they’ll handle L2CP frames and be prepared to adjust accordingly.
So what things should you consider (or ask) when purchasing BT Carrier Ethernet (MetroEthernet) services for your Enterprise? Consider your architecture.
Do you need just a few point to point links? Point to point links may need to be replicated many times to connect more than a couple of offices to each other. If you have more than a few offices, an E-Tree or E-Lan service may be a more efficient option for you. Consider the number of VLANs you wish to push across these links. Do you need separate VLANs for phones, file sharing, videoconferencing, datacenter replication? Try to pin down a rough number of VLANs you’ll need to push (and the carrier will need to preserve from end to end. If you’re considering a multipoint to multipoint solution, ask yourself whether ALL points need to talk to all points? This will likely help you decide between E-LAN or E-Tree. Finally, consider your security position. This whole time I’ve spoken about these services as if they are extensions of your local LAN, but it’s important to consider that the traffic IS leaving your locally controlled hardware and links, and it’s traversing the provider’s (shared infrastructure). Indeed, it may be crossing the networks of more than one global provider. Your own internal security positions or policies may very likely dictate that some or all of this traffic still has to be processed by a firewall before it leaves the headquarters and local branches to get on the Carrier Ethernet service.
Carrier Ethernet services can be incredibly powerful, and intuitive extensions of your enterprise LAN. Because the services mimic the LAN technologies that your network staff already use day to day, they can be deployed quickly and monitored with your existing staff and tools. They are employed by providers worldwide and are inexpensive, and ubiquitous.
They don’t require a new team of WAN experts, but they do require some forethought and planning. I wish you the best of luck in your search and hope our Network Union team are able to assist.
If your business needs to buy or resell BT Business or Wholesale products, a relationship with The Network Union will support you every step of the way.
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