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MPLS VPN QoS Design and Case Study
MPLS VPN QoS design typically is viewed from two distinct perspectives:
- The enterprise customer subscribing to the MPLS VPN service
- The service provider provisioning edge and core QoS within the MPLS VPN service
To achieve end-to-end service levels, enterprise and service-provider QoS policies must be consistent and complimentary. Therefore, QoS considerations and design recommendations for both the enterprise and service provider are presented in this chapter. The following topics are discussed:
- Enterprise-to-service provider mapping models
- Service provider-to-enterprise models
- MPLS DiffServ tunneling modes
- DiffServ in the backbone
- MPLS traffic engineering
MPLS is a combination of routing and switching technologies that can provide scalable VPNs with end-to-end quality of service.
Many customers are turning to service providers that offer MPLS VPN services as private WAN alternatives. One of the main reasons for this is the any-to-any connectivity capabilities of MPLS VPNs. However, this full-mesh nature in itself poses significant QoS implications to enterprise customers and service providers alikenamely, that they both need to comanage QoS in a cooperative and complementary fashion to achieve end-to-end service levels.
This chapter examines in detail QoS considerations that enterprise customers need to bear in mind when subscribing to MPLS VPNs, including how best to map into various service-provider MPLS VPN QoS models.
Service provider-edge QoS considerations are reviewed in depth, including egress queuing models and MPLS DiffServ tunneling modes (Uniform, Short Pipe, and Pipe). Furthermore, service-provider core QoS considerations are reviewed, including aggregate bandwidth provisioning and DiffServ in the backbone. MPLS traffic engineering as it relates to QoS is covered, along with two detailed examples: MPLS per-VPN traffic engineering and MPLS DiffServ traffic engineering.
This chapter concludes with a case study that shows how these designs can be combined in a complex MPLS VPN end-to-end scenario.
Note
This chapter addresses QoS design for MPLS VPNs, not the theory and operation of MPLS VPNs themselves. It is assumed that the reader is familiar with basic MPLS VPN architectures and technologies. For a detailed discussion of MPLS VPNs, refer to the Cisco Press books MPLS and VPN Architectures, Volumes I and II, by Ivan Pepelnjak and Jim Guichard; Traffic Engineering with MPLS, by Eric Osborne and Ajay Simha; and Advanced MPLS Design and Implementation, by Vivek Alwayn.
Case Study: MPLS VPN QoS Design (CE/PE/P Routers)
Continuing the example from the previous design chapters, the fictitious company ABC, Inc., has been growing and expanding, both geographically and technologically. It has multiple data centers in geographically diverse regions to which its field needs to connect efficiently. Additionally, to increase collaboration and simultaneously reduce travel expenses, ABC, Inc., plans to roll out any-to-any videoconferencing. For these business reasons, ABC, Inc., has decided to migrate from its private WAN to an MPLS VPN, managed by service provider XYZ (SP XYZ).
To minimize the costs of migration, SP XYZ supports both Frame Relay and ATM Layer 2 access (including ATM IMA, which has been ABC, Inc.'s, primary choice for branch WAN media).
Furthermore, SP XYZ is a leader in MPLS VPN services and supports a five-class provider-edge model. Real-time service can be purchased in 5 percent increments, as can the amounts of the three other levels of preferred service (Critical Data, Video, and Bulk Data). ABC Inc. wants its WAN migration to MPLS VPN to be as transparent to end users as possible, so it agrees to purchase these services in amounts that closely match the current QoS Baseline WAN edge model, without causing traffic class-mixing issues.
Additionally, ABC, Inc., monitors network utilization (particularly videoconferencing traffic) and performs traffic accounting and department bill-back based on the DSCP markings of traffic flows. ABC, Inc., views it as essential that the SP not re-mark any traffic at Layer 3 as it traverses the MPLS VPN, but rather preserve the DSCP markings intact. Again, SP XYZ can accommodate ABC, Inc., because it deploys the popular Short Pipe Mode of MPLS DiffServ tunneling.
SP XYZ also offers the option of premium service for voice traffic to geographically adjacent sites (through MPLS DS-TE). Because ABC, Inc., is a heavy IP telephony user, it elects to purchase this premium service for voice traffic (thus, from SP XYZ's perspective, ABC, Inc., is considered a "BLUE" class customer).
it is assumed that traffic has been marked correctly on campus/branch switches before it arrives at the CE LAN edges. Where such an assumption is invalid, ingress LAN edge marking policies, discussed in "Branch Router QoS Design," can be applied to the CE LAN edges. Additionally, it has been assumed that there are no unidirectional applications in this example.
Queuing and marking policies for a five-class provider-edge model have been applied on CE edges.
On ingress, SP XYZ applies a five-class short pipe MPLS DiffServ tunneling mode policer to identify (through MPLS EXP values) traffic that is in contract or out-of-contract. DiffServ policies are applied throughout the MPLS VPN core, and MPLS DS-TE also is provisioned for voice traffic to geographically adjacent CEs. On egress, SP XYZ applies a five-class provider-edge model, which is based on the customer's DiffServ markings. In this example, company ABC, Inc., fits service provider XYZ's customer Blue profile.
The configuration for this example spans six routers: Blue-CE1, Blue-CE2, Red-CE1, Red-CE2, PE1, PE2, and P router. However, because CE configurations are virtually identical, only one is presented here .
Configuration :Verification commands:
- show ip rsvp interface
- show ip rsvp neighbor
- show mpls interface
- show mpls traffic-eng tunnels summary
- show mpls traffic-eng tunnels
- show mpls traffic-eng topology
- show ip bgp vpnv4 all
- ping vrf with show interface tunnel
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