CS计算机代考程序代写 assembly Instructor Materials Chapter X: Chapter Title

Instructor Materials Chapter X: Chapter Title

Chapter 2: Point-to-Point Connections
Connecting Networks

Presentation_ID
‹#›
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
1
Cisco Networking Academy Program
Connecting Networks
Chapter 2: Point-to-Point Connections

Chapter 2 – Sections & Objectives
2.1 Serial Point-to-Point Overview
Configure HDLC encapsulation.
2.2 PPP Operation
Explain how PPP operates across a point-to-point serial link.
2.3 PPP Implementation
Configure PPP encapsulation.
2.4 Troubleshoot WAN Connectivity
Troubleshoot PPP.

Presentation_ID
‹#›
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
2

2.1 Serial Point-to-Point Overview

Presentation_ID
‹#›
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
3
Cisco Networking Academy Program
Connecting Networks
Chapter 2: Scaling VLANs

Serial Point-to-Point Overview
Serial Communications
Point-to-point connections are used to connect LANs to service provider WANs, and to connect LAN segments within an enterprise network.
A point-to-point link can connect two geographically distant sites, such as a corporate office in New York and a regional office in London.
Serial connection bandwidths can be incrementally increased to accommodate the need for faster transmission.

Presentation_ID
‹#›
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
4
2.1 – Serial Point-to-Point Overview
2.1.1 – Serial Communications

On each WAN connection, data is encapsulated into frames before crossing the WAN link.
HDLC is the default encapsulation type on point-to-point connections, dedicated links, and circuit-switched connections when the link uses two Cisco devices.
HDLC defines a Layer 2 framing structure that allows for flow control and error control through the use of acknowledgments.
HDLC uses a frame delimiter, or flag, to mark the beginning and the end of each frame
Cisco HDLC frames contain a field for identifying the network protocol being encapsulated.

Serial Point-to-Point Overview
HDLC Encapsulation

Presentation_ID
‹#›
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
5
2.1 – Serial Point-to-Point Overview
2.1.2 – HDLC Encapsulation

Serial Point-to-Point Overview
HDLC Encapsulation
There are two steps to re-enable HDLC encapsulation:
Step 1. Enter the interface configuration mode of the serial interface.
Step 2. Enter the encapsulation hdlc command to specify the encapsulation protocol on the interface.
The show interfaces serial command returns one of six possible states:
Serial x is up, line protocol is up
Serial x is down, line protocol is down
Serial x is up, line protocol is down
Serial x is up, line protocol is up (looped)
Serial x is up, line protocol is down (disabled)
Serial x is administratively down, line protocol is down
The show controllers command is another important diagnostic tool when troubleshooting serial lines.
The output indicates the state of the interface channels and whether a cable is attached to the interface.

Presentation_ID
‹#›
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
6
2.1 – Serial Point-to-Point Overview
2.1.2 – HDLC Encapsulation

2.2 PPP Operation

Presentation_ID
‹#›
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
7
Cisco Networking Academy Program
Connecting Networks
Chapter 2: Point-to-Point Connections

PPP Operation
Benefits of PPP
Use PPP encapsulation to connect a Cisco router to a non-Cisco router.
PPP Advantages
The link quality management feature monitors the quality of the link. If too many errors are detected, PPP takes the link down.
PPP supports PAP and CHAP authentication.

Presentation_ID
‹#›
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
8
2.2 – PPP Operation
2.2.1 – Benefits of PPP

PPP Operation
LCP and NCP
PPP Layered Architecture
PPP and OSI share the same physical layer, but PPP distributes the functions of LCP and NCP differently.
The only absolute requirement imposed by PPP is a full-duplex circuit, either dedicated or switched, that can operate in an asynchronous or synchronous bit-serial mode.
Most of the work done by PPP happens at the data link and network layers, by LCP and NCPs.
Link Control Protocol
LCP establishes the point-to-point link.
LCP also negotiates and sets up control options on the WAN data link, which are handled by the NCPs.
After the link is established, PPP also uses LCP to agree automatically on encapsulation formats such as authentication, compression, and error detection

Presentation_ID
‹#›
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
9
2.2 – PPP Operation
2.2.2 – LCP and NCP

PPP Operation
LCP and NCP
Network Control Protocol
PPP permits multiple network layer protocols to operate on the same communications link.
For every network layer protocol used, PPP uses a separate NCP
Each NCP manages the specific needs required by its respective network layer protocols.
A PPP frame consists of six fields:

Presentation_ID
‹#›
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
10
2.2 – PPP Operation
2.2.2 – LCP and NCP

PPP Operation
PPP Sessions
There are three phases of establishing a PPP session
Phase 1: Link establishment and configuration negotiation
Phase 2: Link quality determination (optional)
Phase 3: Network layer protocol configuration negotiation
LCP operation uses three classes of LCP frames to accomplish the work of each of the LCP phases:
Link-establishment frames establish and configure a link.
Link-maintenance frames manage and debug a link.
Link-termination frames terminate a link.
PPP can be configured to support optional functions:
Authentication
Compression
Multilink

Presentation_ID
‹#›
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
11
2.2 – PPP Operation
2.2.3 – PPP Sessions

PPP Operation
PPP Sessions
After LCP has established the link, the routers exchange IPCP messages
Compression
IPv4-Address

Presentation_ID
‹#›
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
12
2.2 – PPP Operation
2.2.3 – PPP Sessions

LCP and NCP
PPP Layered Architecture
LCP sets up the PPP connection and its parameters
NCPs handle higher layer protocol configurations
LCP terminates the PPP connection

Presentation_ID
‹#›
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
13
3.2.2.1 PPP Layered Architecture

LCP and NCP
PPP Control Protocol (LCP)
LCP provides automatic configuration of the interfaces at each end, including:
Handling varying limits on packet size.
Detecting common misconfiguration errors.
Terminating the link.
Determining when a link is functioning properly or when it is failing.

Presentation_ID
‹#›
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
14
3.2.2.2 PPP – Link Control Protocol (LCP)

LCP and NCP
PPP Network Control Protocol (NCP)
PPP permits multiple network layer protocols to operate on the same communications link.
For every network layer protocol used, PPP uses a separate NCP.

Presentation_ID
‹#›
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
15
3.2.2.3 PPP – Network Control Protocol (NCP)

PPP Sessions
Establishing a PPP Session
Phase 1 – LCP must first open the connection and negotiate configuration options; it completes when the receiving router sends a configuration-acknowledgment frame back to the router initiating the connection.

Presentation_ID
‹#›
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
16
3.2.3.1 Establishing a PPP Session

PPP Sessions
Establishing a PPP Session (cont.)
Phase 2 – LCP tests the link to determine whether the link quality is sufficient to bring up network layer protocols.

Presentation_ID
‹#›
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
17
3.2.3.1 Establishing a PPP Session

PPP Sessions
Establishing a PPP Session (cont.)
Phase 3 – After the LCP has finished the link quality determination phase, the appropriate NCP can separately configure the network layer protocols, and bring them up and take them down at any time.

Presentation_ID
‹#›
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
18
3.2.3.1 Establishing a PPP Session

LCP Operation
LCP operation includes: link establishment, link maintenance, and link termination.
LCP operation uses three classes of LCP frames one for each of the LCP phases:
Link-establishment frames establish and configure a link.
Configure-Request, Configure-Ack, Configure-Nak, and Configure-Reject
Link-maintenance frames manage and debug a link.
Code-Reject, Protocol-Reject, Echo-Request, Echo-Reply, and Discard-Request
Link-termination frames terminate a link.
Terminate-Request and Terminate-Ack

During link maintenance, LCP use messages to provide feedback and test the link.
Echo-Request, Echo-Reply, and Discard-Request can be used to test the link.
Code-Reject and Protocol-Reject provides feedback when one device receives an invalid frame due to either an unrecognized LCP code (LCP frame type) or a bad protocol identifier.

Presentation_ID
‹#›
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
19
3.2.3.2 LCP Operation

PPP Sessions
LCP Operation (cont.)

Presentation_ID
‹#›
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
20
3.2.3.2 LCP Operation

PPP Sessions
LCP Packet

Presentation_ID
‹#›
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
21
3.2.3.3 LCP Packet

PPP Sessions
LCP Packet

Presentation_ID
‹#›
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
22
3.2.3.3 LCP Packet

PPP Sessions
LCP Packet (cont.)

Presentation_ID
‹#›
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
23
3.2.3.3 LCP Packet

PPP Sessions
PPP Configuration Options

Optional functions include:
Authentication using either PAP or CHAP
Compression using either Stacker or Predictor
Multilink that combines two or more channels to increase the WAN bandwidth

Presentation_ID
‹#›
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
24
3.2.3.4 PPP Configuration Options

PPP Sessions
NCP Explained

Presentation_ID
‹#›
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
25
3.2.3.5 NCP Explained

Configure PPP
PPP Configuration Options
Authentication – Two authentication choices are Password Authentication Protocol (PAP) and Challenge Handshake Authentication Protocol (CHAP).
Compression – Increases the effective throughput on PPP connections by reducing the amount of data in the frame that must travel across the link. The protocol decompresses the frame at its destination. Two compression protocols available in Cisco routers are Stacker and Predictor.
Error detection – Identifies fault conditions. The Quality and Magic Number options help ensure a reliable, loop-free data link. The Magic Number field helps in detecting links that are in a looped-back condition. Magic numbers are generated randomly at each end of the connection.

Presentation_ID
‹#›
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
26
3.3.1.1 PPP Configuration Options

Configure PPP
PPP Configuration Options
PPP Callback – PPP callback is used to enhance security. With this LCP option, a Cisco router can act as a callback client or a callback server. The client makes the initial call, requests that the server call it back, and terminates its initial call. The callback router answers the initial call and makes the return call to the client based on its configuration statements. The command is ppp callback [accept | request].
Multilink – This alternative provides load balancing over the router interfaces that PPP uses. Multilink PPP provides a method for spreading traffic across multiple physical WAN links while providing packet fragmentation and reassembly, proper sequencing, multivendor interoperability, and load balancing on inbound and outbound traffic.

Presentation_ID
‹#›
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
27
3.3.1.1 PPP Configuration Options

Configure PPP
PPP Basic Configuration Command

Presentation_ID
‹#›
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
28
3.3.1.2 PPP Basic Configuration Command

Configure PPP
PPP Compression Commands

Presentation_ID
‹#›
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
29
3.3.1.3 PPP Compression Commands

Configure PPP
PPP Link Quality Monitoring Command

The ppp quality percentage command ensures that the link meets the quality requirement set; otherwise, the link closes down.

Presentation_ID
‹#›
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
30
3.3.1.4 PPP Link Quality Monitoring Command

Configure PPP
PPP Multilink Commands

Presentation_ID
‹#›
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
31
3.3.1.5 PPP Multilink Commands

Configure PPP
Verifying PPP Configuration

Presentation_ID
‹#›
© 2008 Cisco Systems, Inc. All rights reserved.
Cisco Confidential
32
3.3.1.6 Verifying PPP Configuration

Configure PPP
Verifying PPP Configuration (cont.)

The output indicates the interface Multilink 1, the hostnames of both the local and remote endpoints, and the serial interfaces assigned to the multilink bundle.

PPP Authentication
PPP Authentication Protocols

PPP Authentication
Password Authentication Protocol (PAP)
Initiating PAP
Completing PAP

PPP Authentication
Challenge Handshake Authentication Protocol
Initiating CHAP
Responding CHAP

PPP Authentication
CHAP (cont.)
Completing CHAP

CHAP sends hash of password and a known random number not the password itself. Hence much more secure than PAP (which sends password in plain text).

2.3 PPP Implementation

PPP Implementation
Configure PPP
PPP may include several LCP options:
Authentication, Compression, Error detection, PPP Callback, and Multilink
To set PPP as the encapsulation method used by a serial interface, use the encapsulation ppp interface configuration command.
Point-to-point software compression on serial interfaces can be configured after PPP encapsulation is enabled with the compress command.
The ppp quality percentage command ensures that the link meets the quality requirement set; otherwise, the link closes down.

PPP Implementation
Configure PPP
MPPP allows packets to be fragmented and sends these fragments simultaneously over multiple point-to-point links to the same remote address.
Configuring MPPP requires two steps:
Step 1. Create a multilink bundle.
Step 2. Assign interfaces to the multilink bundle.

Use the show interfaces serial command to verify proper configuration of HDLC or PPP encapsulation

PPP Implementation
Configure PPP Authentication
RFC 1334, PPP Authentication Protocols, defines two protocols for authentication, PAP and CHAP.
PAP is a very basic two-way process. There is no encryption. The username and password are sent in plaintext.
CHAP is more secure than PAP. It involves a three-way exchange of a shared secret.
To specify the order in which the CHAP or PAP protocols are requested on the interface, use the ppp authentication interface configuration command. Use the no form of the command to disable this authentication.
The PAP username and password that each router sends must match those specified with the username name password password command of the other router.

2.4 Troubleshoot WAN Connectivity

Troubleshoot WAN Connectivity
Troubleshoot PPP
A debug output displays information about various router operations, related traffic generated or received by the router, and any error messages.
Debug ppp
Use the debug ppp command to display information about the operation of PPP.
A good command to use when troubleshooting serial interface encapsulation is the debug ppp packet command.
The debug ppp negotiation command enables the network administrator to view the PPP negotiation transactions, identify the problem or stage when the error occurs, and develop a resolution.
The debug ppp error command is used to display protocol errors and error statistics associated with PPP connection negotiation and operation.

Troubleshoot WAN Connectivity
Troubleshoot PPP
Debug PPP Authentication
Always verify your configuration with the show interfaces serial command, in the same way as you did without authentication.
Never assume your authentication configuration works without testing it using the previously covered show commands
For debugging PPP authentication, use the debug ppp authentication command.

2.4 Chapter Summary

Chapter Summary
Summary
Serial transmissions sequentially send one bit at a time over a single channel. A serial port is bidirectional. Synchronous serial communications require a clocking signal.
Point-to-Point links are usually more expensive than shared services; however, the benefits may outweigh the costs. Constant availability is important for some protocols, such as VoIP.
SONET is an optical network standard that uses STDM for efficient use of bandwidth. In the United States, OC transmission rates are standardized specifications for SONET.
The bandwidth hierarchy used by carriers is different in North America (T-carrier) and Europe (E-carrier). In North America, the fundamental line speed is 64 kbps, or DS0. Multiple DS0s are bundled together to provide higher line speeds.
The demarcation point is the point in the network where the responsibility of the service provider ends and the responsibility of the customer begins. The CPE, usually a router, is the DTE device. The DCE is usually a modem or CSU/DSU.

Summary Continued
Cisco HDLC is a bit-oriented synchronous data link layer protocol extension of HDLC and is used by many vendors to provide multiprotocol support. This is the default encapsulation method used on Cisco synchronous serial lines.
Synchronous PPP is used to connect to non-Cisco devices, to monitor link quality, provide authentication, or bundle links for shared use. PPP uses HDLC for encapsulating datagrams. LCP is the PPP protocol used to establish, configure, test, and terminate the data link connection. LCP can optionally authenticate a peer using PAP or CHAP. A family of NCPs are used by the PPP protocol to simultaneously support multiple network layer protocols. Multilink PPP spreads traffic across bundled links by fragmenting packets and simultaneously sending these fragments over multiple links to same remote address, where they are reassembled.
PPP optionally supports authentication using PAP, CHAP, or both PAP and CHAP protocols. PAP sends authentication data in plaintext. CHAP uses a 3-way handshake, periodic challenge messaging, and a one-way hash that helps protect against playback attacks.

/docProps/thumbnail.jpeg

Related Posts