GP: As it is an open question, I will try to limit it to my networking expertise only. By education I am a data networking person, but the first few years of my career I spent in voice communications. Then, about 12 years ago, life brought me to data networking, completing a circle of life (is it really?). My experiences are with large enterprise customers, ISPs, training partners, and vendors. I find it quite interesting to observe how the subjects of importance do change with the change of who do you work for - a customer, a provider, or a vendor. I find that every experience bares with it certain advantages and allows my growth to continue. Within the last few years I discovered great satisfaction in teaching and consulting. My networking interests do lie in VPNs, their applicabilities to customer networks, routing protocols, and voice and data convergence (will it finally happen? :)).

GP: I find the subject of VPNs in general as being a fascinating topic, interpretation of which changes as time marches on. Not that long ago VPNs were sold over Frame Relay and ATM clouds. I think that VPN is one of those terms that is being used, overused, and reused. With the growth of Internet, L3VPN offerings can be a great business opportunity for ISPs to create value-add services, where they can guarantee CoS to various customers, based on various price structures. My main source of interest in L3VPN started from my interest in ATM, as L3VPN reminds me of the connection-oriented nature of ATM. L3VPN uses MPLS, which is "ATM without cells". Furthermore, L3VPNs over traffic engineered links remind of ATM SVCs.

GP: I think that the most important thing to consider when dealing with L3VPNs is its applicability to the customer. Is the customer really seeking the Layer 3 or Layer 2 solution? I guess what I am trying to say is - L3VPN implies that the provider will participate in customer's routing, while L2VPNs rely on the provider to provide only Layer 2 means of communication. It is very important to distinguish between the two, when dealing with customers and trying to find the best solution for the customer.

GP: I think there are several challenges associated with L3VPNs - complexity and training the staff to operate and maintain it, security or the lack their of, and the customer expectations. L3VPNs, although could be over simple topologies, can be quite complex. A provider must be able not to only implement it, but support it as well. Also, it is very important to manage customer expectations. Prior to any engagement of new service, a customer must be fully aware of what the responsibility of the provider is and visa versa. Questions like, will a provider have monitoring capability so that the customer can "see" what is going on, or will the provider have management reporting indicating the service levels for this VPN, etc, should all be addressed before any agreements are signed. Furthermore, L3VPNs do not imply security. I think it is very important to identify what the word "security" means to the customer. Some people are just concerned with the fact that "my routes will not be intermixed with other routes", while other people are thinking of encryption. L3VPNs can intermix with encryption tunnels, but that could be another offering from the service provider's point of view.

GP: L3VPNs involve a lot of underlying protocols, such as BGP, MBGP, MPLS, IGPs, RSVP, LDP, and finally IP. It is very important to understand them all in order to understand how L3VPNs are actually working. I look at it as peeling an onion, where L3VPN is the outer layer. You unravel the top, and then look inside and see another layer, which has to be peeled off. Also, it is quite important to realize that anything complex consists of smaller less complex parts, and once you understand those less complex parts, the more complex thing will appear to be simpler as well.