Week10 wan-2017(1)
- 1. Lecture 10 – Wide Area Networks DCN330 Fall 2017 Lisa Li
- 2. Outline DCN330 Fall 2017 Common WAN Terminology WAN Connection Types WAN Support Data Terminal Equipment and Data Communication Equipment High-Level Data-Link Control (HDLC) Protocol Point-to-Point Protocol (PPP) Verifying and Troubleshooting Serial Links 2
- 3. Common WAN Terminology Customer premises equipment (CPE): is equipment that’s typically owned by the subscriber and located on the subscriber’s premises. DCN330 Fall 2017 4
- 4. Common WAN Terminology Demarcation point: A point established in a building or complex to separate customer equipment from service provider equipment. Physically, the demarcation point is the cabling junction box, located on the customer premises, that connects the CPE wiring to the local loop. It is usually placed for easy access by a technician. The demarcation point is the place where the responsibility for the connection changes from the user to the service provider. When problems arise, it is necessary to determine whether the user or the service provider is responsible for troubleshooting or repair. DCN330 Fall 2017 5
- 5. Common WAN Terminology Data communications equipment (DCE): Also called data circuit-terminating equipment, the DCE consists of devices that put data on the local loop. The DCE primarily provides an interface to connect subscribers to a communication link on the WAN cloud.. DCN330 Fall 2017 6
- 6. Common WAN Terminology Data terminal equipment (DTE): The customer devices that pass the data from a customer network or host computer for transmission over the WAN. The DTE connects to the local loop through the DCE. DCN330 Fall 2017 7
- 7. Common WAN Terminology Local loop: The actual copper or fiber cable that connects the CPE to the CO of the service provider. The local loop is also sometimes called the “last mile.” DCN330 Fall 2017 8
- 8. Common WAN Terminology Central office (CO): The CO is the local service provider facility or building that connects the CPE to the provider network. DCN330 Fall 2017 9
- 9. Common WAN Terminology Toll network: This consists of the long-haul, all-digital, fiber-optic communications lines, switches, routers, and other equipment inside the WAN provider network. DCN330 Fall 2017 10
- 10. WAN Connection Types DCN330 Fall 2017 11
- 11. WAN Support Physical Layer Standards EIA/TIA-232, EIA/TIA-449, V.24, V.35, X.21, T1, T3, E1, E3, SONET, SDH Data Link Layer Standards and Protocols HDLC PPP Frame-Relay ATM Carrier Ethernet DCN330 Fall 2017 12
- 12. WAN Support (cont’d) DCN330 Fall 2017 14
- 13. WAN Support (cont’d) Router Serial WAN Connectors Examples DCN330 Fall 2017 15
- 14. WAN Support (cont’d) DCN330 Fall 2017 Cisco supports many layer 2 WAN encapsulations on its serial interfaces, including HDLC (High-Level Data Link Control), PPP (Point-to-Point Protocol), and Frame Relay. 16
- 15. Data Terminal Equipment and Data Communication Equipment By default, router interfaces are typically data terminal equipment (DTE), and they connect into data communication equipment (DCE) like a channel service unit/data service unit (CSU/DSU) using a V.35 connector. 18 In a production environment, the DCE network includes the CSU/DSU, through the provider’s wiring and switches, all the way to the CSU/DSU at the other end. The network’s DCE device (CSU/DSU) provides clocking to the DTE-connected interface (the router’s serial interface).
- 16. High-Level Data-Link Control (HDLC) Protocol If you run the command sh int s0/0/0, you probably will notice the HDLC information is shown as follows (notice that you won’t see the encapsulation info by running show running-config (or sh run): HDLC is the default encapsulation used by Cisco routers over synchronous serial links. And Cisco’s HDLC is proprietary, meaning it won’t communicate with any other vendor’s HDLC implementation. But don’t give Cisco grief for it—everyone’s HDLC implementation is proprietary. DCN330 Fall 2017 20
- 17. Point-to-Point Protocol (PPP) The basic purpose of PPP is to transport layer 3 packets across a Data Link layer point-to- point link, and it’s nonproprietary. Plus, since PPP can encapsulate several layer 3 routed protocols and provide authentication, dynamic addressing, and callback, PPP could actually be the best encapsulation solution for you over HDLC. DCN330 Fall 2017 21
- 18. Point-to-Point Protocol (PPP) (cont’d) PPP protocol stack is specified at the Physical and Data Link layers only. Network Control Protocol (NCP) is used to allow communication of multiple Network layer protocols by identifying and encapsulating the protocols across a PPP data link. Link Control Protocol (LCP) offers different PPP encapsulation options, including: authentication, compression, error detection, multilink (supported since IOS v11.1), and PPP callback. DCN330 Fall 2017 22 Figure 21-10: Point-to-Point Protocol stack
- 19. PPP Session Establishment When PPP connections are started, the links go through three phases of session establishment, shown as: DCN330 Fall 2017 23
- 20. PPP Authentication Methods There are two methods of authentication that can be used with PPP links: Password Authentication Protocol (PAP) is the less secure of the two methods. Passwords are sent in clear text and PAP is performed only upon the initial link establishment. When the PPP link is first established, the remote node sends the username and password back to the originating target router until authentication is acknowledged. Challenge Handshake Authentication Protocol (CHAP) is used at the initial startup of a link and at periodic checkups on the link to ensure that the router is still communicating with the same host. After PPP finishes its initial link-establishment phase, the local router sends a challenge request to the remote device. The remote device sends a value calculated using a one-way hash function called MD5. The local router checks this hash value to make sure it matches. If the values don’t match, the link is immediately terminated. DCN330 Fall 2017 24
- 21. PPP Authentication Configuration To configure it from the CLI, use these simple router commands: After you configure your serial interface to support PPP encapsulation, you can then configure authentication using PPP between routers. Set the hostname of the router if it hasn’t been set already. After that, you set the username and password for the remote router that will be connecting to your router, like this: Remember to configure it similarly on the other router, e.g., the router with hostname RouterB. DCN330 Fall 2017 25
- 22. PPP Authentication Configuration (Cont’d) Now, after you’ve set the hostname, usernames, and passwords, choose either CHAP or PAP as the authentication method: Remarks: when using the username command, remember that the username is the hostname of the remote router that’s connecting to your router. And it’s case sensitive too. Also, the password on both routers must be the same. It’s a plain-text password that you can see with a show run command, and you can encrypt the password by using the command service password-encryption (note: run it in the global configuration mode). You must have a username and password configured for each router you plan to connect to. DCN330 Fall 2017 26
- 23. PPP Authentication Configuration (Cont’d) You can start verifying the configuration with the show interface command, e.g. Debugging PPP Authentication To display the CHAP authentication process as it occurs between two routers in the network, just use the command debug ppp authentication. DCN330 Fall 2017 27
- 24. PPP Authentication Configuration (Cont’d) Example DCN330 Fall 2017 28