FREE CCNA LAB

The purpose of this lab is to provide a better understanding of WAN technologies, how to configure and troubleshoot them on Cisco routers. In this lab will explore several types of WAN including HDLC, PPP, and Frame-Relay. This knowledge is essential to passing the CCNA exam and will be used in daily in your position as a Cisco network engineer.

Overview:

A wide area network (WAN) is a network that covers a broad area such as metropolitan, regional, or national and international boundaries. Wide area network may be privately owned or rented but typically computers connected to a wide-area network are frequently connected through public networks, such as the telephone system. They can also be connected through leased lines or satellites. The largest WAN in existence is the Internet.

Learning Objectives:

• Review basic router and switch configuration.
• Configure back-to-back serial connections.
• HDLC Encapsulation.
• PPP Encapsulation.
• PPP Authentication using PAP.
• PPP Authentication using CHAP.

WAN Technologies:

HDLC Encapsulation:

The HDLC protocol is a general purpose protocol which operates at the data link layer of the OSI reference model. The protocol uses the services of a physical layer, and provides either a best effort or reliable communications path between the transmitter and receiver (i.e. with acknowledged data transfer). The type of service provided depends upon the HDLC mode which is used.

Each piece of data is encapsulated in an HDLC frame by adding a trailer and a header. The header contains an HDLC address and an HDLC control field. The trailer is found at the end of the frame, and contains a Cyclic Redundancy Check (CRC) which detects any errors which may occur during transmission. The frames are separated by HDLC flag sequences which are transmitted between each frame and whenever there is no data to be transmitted.

PPP Encapsulation:

PPP (Point-to-Point Protocol) is a protocol for communication between two routers using a serial interface. PPP uses the Internet protocol (IP) (and is designed to handle others). It is sometimes considered a member of the TCP/IP suite of protocols. Relative to the Open Systems Interconnection (OSI) reference model, PPP provides layer 2 (data-link layer) services. Essentially, it packages your TCP/IP packets and forwards them to an upstream router where they can actually be put on the Internet.

PPP is a full-duplex protocol that can be used on various physical media, including twisted pair or fiber optic lines or satellite transmission. It uses a variation of High Speed Data Link Control (HDLC) for packet encapsulation.

Point-to-Point Protocol (PPP) currently supports two authentication protocols: Password Authentication Protocol (PAP) and Challenge Handshake Authentication Protocol (CHAP). Both are specified in RFC 1334 and are supported on synchronous and asynchronous interfaces.

PAP:

PAP provides a simple method for a remote node to establish its identity using a two-way handshake. After the PPP link establishment phase is complete, a username and password pair is repeatedly sent by the remote node across the link (in clear text) until authentication is acknowledged, or until the connection is terminated.

PAP transmits unencrypted ASCII passwords over the network and is therefore considered unsecure. It is used as a last resort when the remote server does not support a stronger authentication protocol, like CHAP or EAP (the latter is actually a framework).

CHAP:

CHAP (Challenge-Handshake Authentication Protocol) is a more secure procedure for connecting to a system than the Password Authentication Procedure (PAP). Here’s how CHAP works:

1. After the link is made, the server sends a challenge message to the connection requestor. The requestor responds with a value obtained by using a one-way hash function.
2. The server checks the response by comparing it its own calculation of the expected hash value.
3. If the values match, the authentication is acknowledged; otherwise the connection is usually terminated.

At any time, the server can request the connected party to send a new challenge message. Because CHAP identifiers are changed frequently and because authentication can be requested by the server at any time, CHAP provides more security than PAP. RFC1334 defines both CHAP and PAP.

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