Appendix A. Questions to Ask Your Provider Regarding Layer 3 IPMPLS VPN Capability

Appendix A. Questions to Ask Your Provider Regarding Layer 3 IP/MPLS VPN Capability

This appendix covers the following topics:

• Coverage and topology

• Customer edge router management

• Network access, resiliency, and load balancing

• QoS capability

• Multicast capability

• Routing protocol capability

• Security

• Software deployment processes

• Interprovider IP/VPN

• IPv6

• MTU considerations

• Hosting capability

• IP telephony PSTN integration

• IP telephony hosted call agent

• Remote and dial access

• Internet access

• Other network services

After you digest all the material in this book, and assuming that you decide to migrate to a Layer 3 virtual private network (VPN) service from a service provider, you need to give some thought to the sorts of questions you will ask about the service offering and what responses will most closely match your needs as an enterprise.

Migrating from a Layer 1 or Layer 2 private WAN to a Layer 3 IP/MPLS VPN should provide all the functionality of a privately built network on top of a service provider's shared intelligent infrastructure. This VPN service should be capable of routing customer IP traffic in an optimal, any-to-any fashion aligned with the physical underlying infrastructure of the provider's network without the need to provision or maintain a full mesh or near-full mesh of individual permanent virtual circuits (PVCs). This eliminates the enterprise's need to perform time-consuming research to determine best points and routes for hub interconnection. In addition, the enterprise needs to perform capacity planning only on a per-port basis, not a per-VC basis.

"Transparency" of the service is a key theme: You should expect any Layer 3 IP/MPLS VPN service to be a "drop-in" replacement of existing network functionality, without significant reengineering of the network. Depending on how the provider has implemented its VPN service, the amount of network reengineering required varies. Typically, the key areas to focus on are as follows:

• Routing protocol support Does the provider offer connectivity using your Interior Gateway Protocol (IGP), or does it require Border Gateway Protocol (BGP) to be supported to its edge devices?

• Multicast support Can the provider's network handle multicast replication, or will generic routing encapsulation (GRE) tunnels need to be created by the enterprise to transport that traffic?

• QoS Can the provider map quality of service (QoS) classes to the existing QoS scheme without loss of original marking? Some remarking may be necessary under certain circumstances, but you need to know what they are when planning a migration.

• Encryption What encryption services are offered as part of the VPN service?

When assessing service provider's capabilities, the following sections are a good collection of questions to consider. It is worth marking absolute requirements for your network in a separate color, such as red, to emphasize their importance. You also should request a full explanation and road map details for any requirement that cannot be fully met today.