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In a previous article, we discussed SR-MPLS and SR-TE and how they dramatically simplify the network, provide Fast Reroute with TI-LFA, and support next-generation traffic engineering capabilities, including delay and constraint-based routing. 

But are these features applicable to enterprise networks?

SONET and DWDM overview

For years, service providers and many enterprises relied on Synchronous Optical Networking (SONET) for automatic protection switching (APS), a feature that provides network-level path protection against failures.

In a SONET network with APS, the protection mechanism allows for the rapid detection and switching of traffic from a working (primary) path to a protect (backup) path in the event of a network failure. The switching time of <50ms is designed to ensure minimal disruption to the traffic flow, providing fast and seamless protection against outages. 

SONET APS played a critical role in ensuring network reliability and continuity by quickly rerouting traffic in case of a failure, thereby minimizing downtime.

SONET is a legacy technology replaced by dense wavelength division multiplexing (DWDM) which increases the bandwidth of fiber optic networks by multiplexing multiple optical carrier signals onto a single fiber.

DWDM technology is used in telecommunications networks and enterprise networks to meet the demand for high-speed and bandwidth data transmission. 

Like SONET, DWDM provides path protection, guaranteeing path switching in <50ms. However, we can reduce complexity and cost by moving the path protection mechanism from the DWDM layer to the IP layer on the router.

SR-MPLS overview

Segment Routing (SR) was first conceived by Cisco in 2014. Since then, it has become the technology of choice for network transport and WAN backbones in service providers and enterprise networks.

SR with Multiprotocol Label Switching (MPLS), referred to as SR-MPLS, is an architecture based on the source routing principle, which allows network operators to steer traffic through a network using a predetermined path. 

SR-MPLS is commonly used in service provider networks. However, look at the enterprise adoption rate in the diagram below, specifically for the industry leader Cisco.

SR is deployed equally in enterprise networks to achieve benefits such as improved network scalability, traffic engineering and simplified network provisioning. In enterprise networks, SR-MPLS can benefit organizations of any size by providing <50ms Fast Reroute capabilities, optimized network resources, enhanced network performance and improved traffic management. 


Segment Routing is deployed equally in enterprise networks to achieve benefits such as improved network scalability, traffic engineering and simplified network provisioning.
Segment Routing is deployed equally in enterprise networks to achieve benefits such as improved network scalability, traffic engineering and simplified network provisioning.

SR-MPLS in the enterprise

Although the decision to deploy SR-MPLS and SR-TE in an enterprise network depends on various factors — such as the size and complexity of the network, the level of traffic engineering requirements, the existing network infrastructure, and the availability of skilled resources to manage and maintain the technology — one thing is sure, and that is the need for fast failover. 

All organizations have voice services and sometimes video services requiring less than 200ms failover times. With the advent of AI, convergence times have become even more critical. IGP routing protocols can take as long as 2 seconds to converge, and with voice, video or real-time data, 2 seconds is unacceptable in modern networks. 

Fast Failover in less than 50ms is not possible without either DWDM Path Protection or IP Fast Reroute. SR-MPLS provides simple IP Fast Reroute in any topology (including rings) via Topology Independent Loop Free Alternate (TI-LFA), as discussed in more depth in a previous article

The benefit of doing protection in the SR-MPLS is that it moves cost and complexity out of the DWDM network and does not require pre-planning. 

Improving failover is critical to all modern enterprise networks and a key driver for SR, making TI-LFA a necessity. 

In addition, TI-LFA is simple to operate and understand, supported by most modern hardware, automatically computed by the IGP, requires no pre-planning and always uses the post-convergence path. It's no surprise that the most significant reason enterprise organizations have chosen SR-MPLS is TI-LFA.

In addition to Fast Reroute, SR-MPLS provides simple and scalable traffic engineering, also known as SR-TE. 

SR-TE is a stateless solution; the path is encoded into the packet, there is no need to build and maintain any tunnel, like previously required with RSVP-TE, and no state is kept in the network. This provides simplicity in terms of deployment and higher scalability for the overall network.

This technology allows network operators to steer traffic in IP/MPLS networks. SR-TE enables explicit path control through the network by steering traffic along specific paths or providing dynamic delay and constraint-based routing in addition to supporting per-flow-based traffic engineering. 

SR-TE can be used in enterprise networks to improve the quality of service, enhance network performance and optimize network traffic; it gives network operators greater control and flexibility in managing traffic; and it enables them to meet the demands of modern networks, especially with the growing interest in AI. 

Cisco product alignment

When enterprises look for WAN routers for transport and services, confusion arises around the different product offerings.

Cisco's flagship operating system, IOS-XR, and their core and edge routers that run IOS-XR are driven out of Cisco's Service Provider Business Unit.

These products include ASR9000/9900, NCS55xx, NCS560/540 and Cisco 8000. These IOS-XR operating systems are top-performing products for port density, power, speed and features. 

Cisco is the industry leader in SR-MPLS and SRv6 features and deployments, and although IOS-XE routers support both protocols, the feature set on the IOS-XR routers is more extensive. 

In addition, IOS-XR is more robust and stable and offers operational simplicity. Service providers and the most prominent enterprises choose IOS-XR-based routers for these reasons. 

Unfortunately, mid-tier and smaller enterprises are not always aware of the IOS-XR routers and sometimes look to other products in the IOS-XE family to fulfill their requirements. 

Coupled with IOS-XR, Cisco routers have unmatched SR-MPLS and SR-v6 feature sets and capabilities, which makes them the industry choice for implementing SR. 


SR comes in two flavors: SR-MPLS and SRv6, and both offer much-needed Fast Reroute and traffic engineering capabilities for today's networks that transport critical services like voice, video, real-time data and AI. Access to Fast Reroute via TI-LFA makes SR necessary for modern enterprise networks. 

Furthermore, SR provides several benefits for network operators and administrators, including network scalability, flexibility, programmability, and operational simplicity. 

Ultimately, SR allows networks to scale into the future by making them resilient, robust and scalable. 

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