Stuart Fordham - Learning SD-WAN with Cisco: Transform Your Existing WAN Into a Cost-effective Network

Stuart Fordham

Learning SD-WAN with Cisco

Transform Your Existing WAN Into a Cost-effective Network

1st ed.

Logo of the publisher

To my wife.

About the Author

Stuart Fordham

CCIE 49337 is the Network Manager and Infrastructure Team Leader for SmartCommunications SC Ltd, the only provider of a cloud-based, next-generation customer communications platform. Stuart has written a series of books on BGP, MPLS, VPNs, and NAT, as well as a CCNA study guide and the Cisco ACI Cookbook. He lives in the UK with his wife and twin sons.

About the Technical Reviewer

David Samuel Pealoza Seijas

works as a Principal Engineer at Verizon Enterprise Solutions in the Czech Republic, focusing on Cisco SD-WAN, ACI, OpenStack, and NFV. Previously, he worked as a Data Center Network Support Specialist in the IBM Client Innovation Center in the Czech Republic. As an expert networker, David has a wide diapason of interests, while his favorite topics include data centers, enterprise networks, and network design, including software-defined networking (SDN).

In this chapter, we are going to look at what SD-WAN is and how it came about.

The networks we rely on for both business and pleasure on a day-to-day basis are susceptible to many factors that can result in a slow and unreliable experience.

We can experience latency , which either refers to the time between a data packet being sent and received or the round-trip time, which is the time it takes for the packet to be sent and for it to get a reply, such as when we use ping.

We can also experience jitter, which is the variance in the time delay between data packets in the network, basically a disruption in the sending and receiving of packets.

We have fixed bandwidth networks that can experience congestion: with 5 people sharing the same Internet link, each could experience a stable and swift network, add another 20 or 30 people onto the same link and the experience will be markedly different.

There are ways we can help manage the experience for all. We can implement quality of service (QoS) , which we can use to prioritize traffic, such as voice and video, where fluctuations in the network due to these factors are noticeable. We can also use QoS to give each user their fair share of bandwidth and to ensure that the right amount of bandwidth is assured for our mission-critical applications.

QoS works well within the boundaries of the network but requires manual intervention. We need to know what our traffic is, where that traffic needs to go, and what our priority traffic is. We can help it get there faster and with a larger degree of assured delivery, but it still requires the network administrators to ensure that the paths the traffic is to take are present, working, and reliable. QoS, combined with policy-based routing (PBR) , can also provide a way to route traffic out of different interfaces, making use of dedicated high-speed links for mission-critical traffic and other links for user traffic such as Internet browsing and media streaming. These do, again, require the network administrator to plan this traffic splitting out, and this method is not exactly dynamic.

There are mechanisms to dynamically route traffic though, such as Multiprotocol Label Switching Traffic Engineering (MPLS-TE) . Through the use of MPLS, a link-state protocol such as OSPF or IS-IS, RSVP (Resource Reservation Protocol ), and CBR (Constraint-Based Routing ), we can have a network that learns about changes in the network and reacts by performing path selection in the network.