Wide Area Network
Course Description
A WAN (Wide Area Network) connects your LANs to each other and to the Internet, over distances from a few kilometers to the other side of the world. In this course, we start with WAN terminology and the different ways service providers forward data: circuit switching, packet switching, and cell switching. You’ll learn about Metro Ethernet and its services, and how to configure HDLC and PPP on serial links, including PAP and CHAP authentication and Multilink PPP. We also cover technologies that you’ll mostly find in older networks today, like Frame Relay, PPPoA for DSL, and 3G, and we look at how Cisco Performance Routing (PfR) selects the best exit path based on delay, loss, and load instead of static metrics.
Course Highlights
In this course you will learn:
- The WAN terminology: CPE, demarc, DTE, DCE, CSU/DSU, local loop, and central office.
- The difference between circuit switching, packet switching, and cell switching.
- How Metro Ethernet works, and the E-Line, E-LAN, and E-Tree services.
- How to configure HDLC and PPP on serial links, with PAP and CHAP authentication.
- How Multilink PPP bundles serial links, and how link fragmentation and interleaving helps VoIP.
- How Frame Relay works with PVCs, DLCIs, and LMI, and how to configure point-to-point and point-to-multipoint.
- How to configure PPPoA for DSL, a PPPoE server, and a 3G wireless WAN connection.
- How Optimized Edge Routing (OER) and Performance Routing (PfR) select the best exit path.
Presented to you by instructor Rene Molenaar, CCIE #41726
Course at a glance
- 19 lessons in 6 units.
- Format: self-paced lessons with Cisco IOS router configurations, debugs, and video.
- Last updated: October 2026.
Requirements
- Basic knowledge of IP addressing and the OSI model.
- For the Performance Routing unit: a good understanding of static routes and routing protocols like OSPF and EIGRP.
Course Schedule
What is a WAN?
A WAN (Wide Area Network) connects networks over a large geographical area: two offices in different cities, branch offices to the headquarters, or your network to the Internet. We own and operate our LANs, but a WAN is usually built and operated by a service provider, like a phone company, cable company, or ISP. You pay for the right to use their network.
On the LAN, Ethernet is the dominant protocol. On the WAN, there are many technologies to choose from, and most of them describe layer 1 and 2 of the OSI model. Some give you a dedicated point-to-point link, like a leased line, while others share the provider’s network between customers, like Frame Relay, MPLS, and Metro Ethernet. Most WAN technologies use packet switching nowadays, which uses the available capacity much better than the circuit switching of the old phone network.
WAN technologies change over time. Leased lines with HDLC or PPP, Frame Relay, ATM, and ISDN were the standard for years, and you’ll still run into them in older networks and labs. Today, most companies connect their sites with Metro Ethernet, MPLS VPNs, or Internet connections like DSL, cable, fiber, and 4G/LTE, often with VPNs or SD-WAN on top. Understanding the older technologies still helps, because many of today’s concepts, like PPP authentication and hub and spoke topologies, come from them.
WAN Learning Roadmap
This roadmap follows the course units. Each topic has a short explanation and links to the lessons where we cover it in detail.
WAN Fundamentals
Before looking at protocols, you need to know the WAN terminology: the CPE at the customer site, the demarcation point where the provider’s wiring ends, the local loop, and the central office. Data can be forwarded with circuit switching, packet switching, or cell switching. Metro Ethernet brings Ethernet to the WAN: from the customer’s perspective, it’s like you are connected to a switch, and the MEF defines services like E-Line, E-LAN, and E-Tree.
Serial Links: HDLC and PPP
HDLC is the default encapsulation on Cisco serial interfaces, but every vendor adds a proprietary field, so it doesn’t work between vendors. PPP is the alternative: LCP sets up the link and takes care of authentication, and NCP lets you run IP, IPv6, and other protocols over it. PAP sends the password in plaintext, while CHAP uses a challenge so the password is never sent. Multilink PPP bundles multiple serial links into a single logical link, and with link fragmentation and interleaving (LFI), small voice packets don’t have to wait behind large data packets.
Frame Relay
Frame Relay was a cheaper alternative to leased lines. Customers share the provider’s network, and permanent virtual circuits (PVCs) connect the sites, often in a hub and spoke topology. Each PVC is identified with a DLCI, and LMI works as a keepalive that tells the router whether a PVC is active. Frame Relay is a legacy technology, but it’s a good way to learn about non-broadcast multi-access networks, and you’ll still see it in older lab topologies. You’ll configure a router as a Frame Relay switch for your lab, and build point-to-point and point-to-multipoint connections between the sites.
Internet Access: DSL, PPPoE and 3G
ISPs kept using PPP when DSL and cable replaced dial-up, because it lets them authenticate users with CHAP and assign an IP address. PPPoA carries PPP over the ATM interface of a DSL router, and PPPoE carries PPP in Ethernet frames. We configure both, including a Cisco router as a PPPoE server. For wireless WAN, we configure a cellular interface for 3G; the configuration is similar for 4G/LTE.
Performance Routing (PfR) and OER
Routing protocols select a path based on static information. OSPF prefers a gigabit link, even when it’s congested and a slower link is idle. Optimized Edge Routing (OER) and its successor, Performance Routing (PfR), look at the current state of the network, like delay, packet loss, and load, and inject routes to send traffic out of the best exit. A master controller and border routers go through five phases in a loop: profile, measure, apply policy, control, and verify. You’ll start with a basic OER configuration, use variance to solve policy conflicts, and shorten the OER timers for your labs. PfR is an older Cisco feature; today, SD-WAN solutions do this kind of path selection.
Frequently Asked Questions
A WAN (Wide Area Network) connects networks over a large geographical area, like offices in different cities or your network to the Internet. WANs are usually operated by service providers, who lease the use of their network to customers. Read our introduction to WANs.
A LAN connects devices that are close to each other, in a building or campus, and you own and operate it yourself. A WAN covers a large area and is usually operated by a service provider. On the LAN, Ethernet is the dominant protocol, while on the WAN there are many different technologies. Learn more about WANs.
With circuit switching, a dedicated circuit with a fixed capacity is reserved for the entire connection, whether you send data or not. With packet switching, data is split into packets that share the network’s capacity, so no capacity is wasted. Packet switching has mostly replaced circuit switching. Learn about WAN switching methods.
Metro Ethernet is a WAN service where the provider gives you an Ethernet connection, so it’s like your sites are connected to the same switch. It was first used in metropolitan areas, which is where the name comes from. The MEF defines services like E-Line (point-to-point), E-LAN (multipoint), and E-Tree (hub and spoke). Learn about Metro Ethernet.
Both are layer 2 protocols for point-to-point serial links. HDLC is the default on Cisco serial interfaces, but because vendors add a proprietary field, it doesn’t work between vendors. PPP is a standard that also supports authentication with PAP or CHAP and can carry multiple layer 3 protocols. Learn how PPP works.
PAP sends the username and password in plaintext over the link. CHAP sends a challenge instead, and the other side answers with a hash, so the password itself is never sent. CHAP is far more secure. See how to configure PAP and CHAP.
Hardly. Frame Relay was a popular, cheaper alternative to leased lines, but providers have replaced it with MPLS, Metro Ethernet, and Internet-based VPNs. You still see it in older networks and labs. Learn how Frame Relay works.
PfR is a Cisco feature that selects the best exit path based on the current state of the network, like delay, packet loss, jitter, and load, instead of the static metrics of routing protocols. It’s the successor of Optimized Edge Routing (OER). Today, SD-WAN solutions offer this kind of path selection. Learn how PfR works.
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