How to configure a basic WAN serial connection

Certification: Cisco CCNA Routing and Switching - Cisco Certified Network Associate Routing and Switching

A Wide Area Network, WAN, is formed when a number of LANs and MANs are interconnected to form a wide network. A WAN is generally spread over a wide geographical area. However, as much intriguing it sounds, the reality is that the setting up and configuration of a WAN connection is quite difficult and required an in-depth understanding of certain topics. In this regard, you need to understand how the settings are configured on the physical layer, data-link layer and the third layer of the OSI model. However, you also need to have detailed information regarding all the components which are used in to establish a WAN serial connection.

One of the most amazing things about cisco serial connection is that it can support almost any type of WAN service. There are basically two encapsulation protocols which are involved in this process. The first one is HDLC (High-Level Data Link Control) Protocol and the second one is the PPP (Point-to-Point Protocol). These two protocols are the most essential components which make up a WAN serial connection. In this regard, it is important to understand their function and learn the way in which both of them can be configured. There are certain commands as well which you need to know in order to perform the process of configuration. Below, you will find details regarding HDLC and PPP and the ways in which they can be configured to form a WAN serial connection.

HDLC Protocol

HDLC protocol is also referred to as High-Level Data Link Control Protocol. This is one of the protocols which operate during the data link layer of the OSI model. HDLC specifies an encapsulation method for serial data links by making use of frame characters. You need to keep in mind that you do not require any authentication with HDLC. It is a point-to-point protocol. In fact, HDLC is one of the most famous bit-oriented protocols in which information is represented using single bits. Furthermore, HDLC is the default encapsulation method used by cisco routers. Hence, it only communicates with other routers of cisco which make use of HDLC. If the routers are using another encapsulation method, a connection would not be established.

Configuration of HDLC

The process of configuration of HDLC on cisco routers is quite simple and easy. You just need to enter a few commands in the prescribed order and your router will be configured with HDLC. In this regard, you will make use of “config” and “config-if” commands and then make adjustments to configure HDLC on the router. You should know that HDLC could only be configured on a Cisco router, and both of the Cisco routers need to have the HDLC encapsulation. If you want to communicate with a non-Cisco router, you will have to use other protocols such as PPP.


PPP is also referred to as Point-to-point protocol. PPP is one of the most famous protocols which are used on the Data link layer. It makes use of a number of protocols to assist it in its purpose. It makes use of LCP, Link control protocol, to create and maintain all data link connections. In addition to this, it also makes use of NCP, Network control protocol, which enables all the protocols on the network layer to be used on the established point-to-point connection. In fact, PPP is one of the most essential components of the data link layer.

There are basically four components which are used by the Point-to-point protocol.

  1. ISDN: It is used on the physical layer of the OSI model. It is used on the physical layer primarily for the purpose of serial communication. Hence, it is an extremely important and widely used component.
  2. LCP: As described above, a Link Control Protocol is used on the data-link layer. The primary purpose of LCP is to configure, maintain and terminate a point-to point connection.
  3. HDLC: HDLC is also used over the data link layer of the OSI model. It primary purpose is to provide an encapsulation method for data over serial links.
  4. NCP: Network Control Protocol also operates at the layer two, data link layer of the OSI Model. It enables a number of network layer protocols to be established and configured. In fact, it allows these network layer protocols to operate simultaneously without any problem or issue. Some of the examples are IPXCP and IPCP.

Hence, these components of PPP operate only at the physical and data link layers of the OSI model. While ISDN operates on the Physical layer; LCP, HDLC and NCP operate on the Data link layer of the OSI model. These components are extremely important in the formation of serial connections. You should also keep in mind that if you want a Cisco router to communicate with a non-Cisco router, you need to configure them both on the PPP. Otherwise, they will not be able to establish a connection in any way.

Configuration of PPP

The configuration of PPP on Cisco routers is an essential process. It is quite easy to perform and very simple as well. In fact, the process of configuration of PPP on Cisco routers is quite similar to the configuration of HDLC on Cisco routers. You will need to enter a number of configuration commands in the prescribed order. These commands are built-in and you just need to type them to perform the configuration. The commands used in this regard are “config” and “config-if”. In order to end the commands, you will have to press CTRL and Z. Once this is done, the Point to Point connection will be configured on your router. You will perform the same process of each router similarly in order to configure it.

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