Interesting questions. Here are a few thoughts from the perspective of an education/research backbone operator that used to be IP only but has also been offering L2 point-to-point circuits for a few years.

Should business customers expect to be able to connect several LANs through an Ethernet L2 ciruit and build a layer 2 network spanning several locations?

At least for our customers, that is indeed important. The most popular application here is for a customer to connect a remote location to their campus network, and that want to (at least be able to) use any of their existing VLANs at the remote site.

Or should the service provider implement port security and limit the number of MAC addresses on the access ports, forcing the customer to connect a router in both ends and segment their network?

That would make the service less attractive, and also more complex to set up and maintain. For point-to-point service, there is really no reason for the network to care about customers' MAC addresses, VLAN tags and such. As you said, EoMPLS doesn't care. (Ethernet over L2TPv3 shouldn't care either. If I had cost-effective edge routers that did L2TPv3 encapsulation/decapsulation at line rate, I'd switch off MPLS in our core tomorrow.) Couldn't PBB or even Q-in-Q provide that isolation as well, at least for point-to-point services? I must say that I don't personally have much experience with those, because we tend to connect our customers to EoMPLS-capable routers directly.

Also, do you see a demand for multi-point layer 2 networks (requiring VPLS), or are point-to-point layer 2 circuits sufficient to meet market demand?

That's a big question for us right now... we're not sure yet. I'd like to hear others' opinions on this.

The most important argument for customers that choose Ethernet L2 over MPLS IP-VPN is that they want full control over their routing, they don't want the involvement from the service provider. Some customers also argue that a flat layer 2 network spanning several locations is a simpler and better design for them, and they don't want the "hassle" with routers and network segmentation.

I have a good deal of sympathy for customers who think this way. Also from the service provider point of view, I like the simplicity of the offering - basically we're providing an emulation of a very long piece of Ethernet cable. (My worry with multipoint L2 VPNs is that they can't have such a simple service model.)

But IMO the customer (and the service provider) is far better off by segmenting their network in the vast majority of cases. What do you think?

Maybe they already have a segmented network, but don't want to segment it based on geography/topology. As far as I'm concerned, enterprises should just connect their various sites to the Internet independently, and use VPN techniques if and where necessary to provide the illusion of a unified network. In practice, this illusion of a single large LAN (or rather, multiple organization-wide LANs) is very important to the typical enterprise, because so much security policy is enforced based on IP addresses. And the typical enterprise wants a central chokepoint that all traffic must go through, for reasons that might have to do with security, or support costs, or with (illusions of) control. This bridging function required to maintain the illusion of a unified network is something that most enterprises prefer to outsource. I'd hope that at some point, better security mechanisms and/or better VPN technologies make these kinds of VPN services less relevant. Until that happens, there's going to be demand for them. Of course the telcos have known that for eons and provided many generations of expensive and hard-to-use services to address this. Point-to-point Ethernet services are interesting because they are relatively easy to provide for folks like us who only really know IP (and maybe some MPLS). And the more transparent they are, the easier it is for customers to use them. -- Simon.

The MEF has a set of specs for this. http://metroethernetforum.org/ In general, it's built as a "dumb pipe" virtual circuit, IE your client BPDUs and other IEEE 802.* signaling are ignored, as they are encapsulated, and forwarded explicitly to a given port. What you do on the switch that gets the deencapsualted traffic is your business. -----Original Message----- From: Endresen Even [mailto:Even.Endresen@bkk.no] Sent: Thursday, December 31, 2009 12:41 AM To: nanog@nanog.org Subject: Restrictions on Ethernet L2 circuits? Hello, Anyone with opinions on what restrictions a service provider should and should not impose on Ethernet L2 circuits provided to business customers wanting to connect several offices? The service provider's MPLS core network doesn't mind what traffic flows through the EoMPLS tunnel, but the L2 access network do mind and can be vulnerable to several layer 2 issues. Broadcast storm control and BPDU filter will protect the access network to a certain degree, but there are still potential layer 2 problems that can affect the switches, for example MAC address spoofing/flooding. Not to mention potentially difficult troubleshooting if a business customer connects two large LANs through the ISP's Ethernet layer 2 circuit, and then experience some occult layer 2 problem. Should business customers expect to be able to connect several LANs through an Ethernet L2 ciruit and build a layer 2 network spanning several locations? Or should the service provider implement port security and limit the number of MAC addresses on the access ports, forcing the customer to connect a router in both ends and segment their network? Also, do you see a demand for multi-point layer 2 networks (requiring VPLS), or are point-to-point layer 2 circuits sufficient to meet market demand? The most important argument for customers that choose Ethernet L2 over MPLS IP-VPN is that they want full control over their routing, they don't want the involvement from the service provider. Some customers also argue that a flat layer 2 network spanning several locations is a simpler and better design for them, and they don't want the "hassle" with routers and network segmentation. But IMO the customer (and the service provider) is far better off by segmenting their network in the vast majority of cases. What do you think? Regards, Even ___________________________________________________ This message and any attachment is intended for the person(s) named above only. It may contain information that is confidential or legally privileged. If you have received this communication in error, please erase all copies of the message and its attachments and notify us immediately. Thank You. This footnote confirms that the email and attachment(s) has been swept by our anti-virus solution for the presence of known computer viruses.