MPLS load sharing and high availability

Multiprotocol Label Switching (MPLS) can be used to create a redundant network architecture, enabling high availability. In this tip, gain a better understanding of MPLS and learn the various components that must be considered when architecting MPLS links.

High availability is essential in a convergent network. If your organization anticipates sending real-time applications

over the infrastructure, that infrastructure must support five nines (99.999%) availability. In this tip, we look at how MPLS can be used to form a redundant architecture for high availability.

MPLS transport background

The current activity going on with MPLS adoption is truly exciting. Sometimes folks have a misunderstanding about MPLS. MPLS transport is the same as any other WAN transport technology in that it connects equipment in one site to equipment in other sites and allows those sites to exchange information. The difference is that MPLS uses IP as the technology to connect the sites, whereas traditional solutions used frame relay, ATM and private line circuits. Confusing things even more is the fact that you can use frame, ATM and private line to connect to the MPLS cloud.

From a transport perspective, one MPLS circuit is in no way a more redundant solution than one frame, ATM or private line circuit -- the point being that redundancy is required for high availability, and high availability is required for convergent applications.

Redundancy components

There are multiple components to redundancy in terms of an MPLS solution, as defined below. Overlying all of this is the IP routing protocol architecture providing rapid convergence and load sharing over the redundant links. Each of these must be considered when architecting that last piece between your organization and the carrier's network.

  • Carrier/local loop redundancy: The circuit from the routers at customer sites will terminate on a MPLS router. True redundancy is dual-carrier, dual-circuit, but the complexities are difficult. Other options include terminating the circuits on separate routers in separate carrier PoPs, dual routers in the same PoP and the same router, different line cards.
  • Customer premise redundancy: This is one router with dual circuits, or dual routers, each with a circuit. Dual routers are definitely recommended. A single router with dual circuits still presents a single point of failure.
  • Routing protocol and IP architecture: This can be any routing protocols supported by the carrier, but BGP is recommended in order to facilitate the load sharing and rapid convergence required for real-time applications.

The IP routing architecture is where organizations struggle most. BGP is the best way to go in terms of supporting key attributes of MPLS as an IP service. BGP can be confusing and appear complex if the organization has not used it before, other than for Internet access. However, when looking to deploy real-time voice, video and other mission-critical applications as an organization, leveraging the high availability and load sharing capabilities of BGP is a best practice for next-generation environments.

The next article in this series will discuss how to enable the routers at the edge of the network to facilitate high availability and load sharing. The focus will be on IP routing architecture for optimizing the MPLS environment.

About the author:
Robbie Harrell (CCIE#3873) is the National Practice Lead for Advanced Infrastructure Solutions for AT&T. He has more than 10 years of experience providing strategic, business and technical consulting services. Robbie lives in Atlanta and is a graduate of Clemson University. His background includes positions as a principal architect at International Network Services, Lucent, Frontway and Callisma.

This was first published in November 2006

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