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Implementing Enterprise WAN Links

Implementing Enterprise WAN Links. Introducing Routing and Switching in the Enterprise – Chapter 7. Objectives. Describe the features and benefits of common WAN connectivity options. Compare and configure common WAN encapsulations. Describe Frame Relay. 7.1 WAN Devices and Technology.

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Implementing Enterprise WAN Links

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  1. Implementing Enterprise WAN Links Introducing Routing and Switching in the Enterprise– Chapter 7

  2. Objectives • Describe the features and benefits of common WAN connectivity options. • Compare and configure common WAN encapsulations. • Describe Frame Relay

  3. 7.1 WAN Devices and Technology • WAN Services purchased • Serial transmissions verses Ethernet in LANS

  4. 7.1 WAN Devices and Technology • Translation device – prepare data for transmission: modem (analog) or CSU/DSU (digital) • Central Office (CO) and Customer Premises Equipment (CPE) • Demarc - point at which responsibility of the customer ends and the service provider begins

  5. 7.1 WAN Devices and Technology • Local loop – last mile (first mile for customer) • CSU/DSU or modem – controls the rate data moves onto the loop (DCE), also provides clocking signal to router (DTE) • Various physical layer protocols used

  6. 7.1 WAN Devices and Technology Note: DS0 – Digital Signal 0, T1 (DS1) = 24 DS0s

  7. Activity 7.1.1.5

  8. Activity 7.1.1.5

  9. 7.1.2 WAN Standards Layer 2 WAN protocols: • LAPF • HDLC • PPP

  10. 7.1.2 WAN Standards Activity 7.1.2.2

  11. 7.1.2 WAN Standards Activity 7.1.2.2

  12. 7.1.3 Accessing the WAN • Modems enable POTS to be used for WAN connections • Modems are also used for DSL and cable connections to ISP • A modem encodes the information onto that carrier wave before transmission and then decodes it at the receiving end • The modulated carrier wave carries information to destination across the telephone network • Destination demodulates the carrier and extracts information

  13. 7.1.3 Accessing the WAN • DSO channel = time slice of the physical bandwidth • Fractional connections – part of a T1 • Two techniques which information from multiple channels can be allocated bandwidth on a single cable based on time: • Time Division Multiplexing (TDM) - if a sender has nothing to say, its time slice goes unused, wasting valuable bandwidth. • Statistical-Time Division Multiplexing (STDM) - dynamically reassigns unused time slices on an as-needed basis, minimizes wasted bandwidth

  14. Activity 7.1.3.4

  15. Activity 7.1.3.4

  16. 7.1.4 Packet and Circuit Switching • Dedicated Leased Line – point-to-point serial • Circuit switching: • Dedicated bandwidth • Higher cost • Higher level of security

  17. 7.1.4 Packet and Circuit Switching • Packet switching: • Bandwidth efficiency • Identifier on each packet • Preconfigured, but non-exclusive, link • Cell switching: • high-speed packet switching • ATM (fixed length cells) • Large amount of overhead

  18. 7.1.4 Packet and Circuit Switching • Virtual circuits • Switched virtual circuits - dynamically established between two points when a router requests a transmission • Permanent virtual circuits - provides a permanent path to forward data between two points (Frame Relay)

  19. 7.1.5 Last mile and long range WAN technologies

  20. 7.1.5 Last mile and long range WAN technologies • Elements of Layer 2 encapsulations • Flag • Address • Control • Protocol • Data • FCS

  21. 7.1.5 Last mile and long range WAN technologies • Great Distances with Fiber • Synchronous Optical Network (SONET) • Synchronous Digital Hierarchy (SDH) • SDH and SONET are used for moving both voice and data. • New developments for extremely long - dense wavelength division multiplexing (DWDM) - can carry IP, SONET, and ATM data concurrently

  22. Activity 7.1.5.3

  23. Activity 7.1.5.3

  24. 7.2.1 Ethernet and WAN Encapsulations • Encapsulation occurs before data travels across the WAN • Layer 2 adds header information specific to the type of physical network transmission • LAN – Ethernet • WAN – depends on link

  25. 7.2.2 Comparing Common WAN Encapsulations • Data Link Layer encapsulation may change continuously to match the technology in use • Network Layer encapsulation will not change • Packets exit the LAN by way of the default gateway router • Router strips off the Ethernet frame and then re-encapsulates that data into the correct frame type for the WAN - acts as a media converter, by adapting the Data Link Layer frame format to a format that is appropriate to the interface

  26. 7.2.2 Comparing Common WAN Encapsulations • Standard bit-oriented Layer 2 encapsulation: HDLC • Cisco HDLC: additional Type field • Default WAN encapsulation on Cisco devices • Allows multiple Network Layer protocols to share a link

  27. 7.2.2 HDLC and PPP Point-to-Point Protocol (PPP): • Data Link Layer encapsulation for serial links • Uses a layered architecture to encapsulate & carry multi-protocol datagrams over a point-to-point link • Standards-based • Support • Asynchronous serial • Synchronous serial • Support High-Speed Serial Interface (HSSI) • Integrated Services Digital Network (ISDN)

  28. 7.2.2 HDLC and PPP • PPP has two sub-protocols: • Link Control Protocol - responsible for establishing, maintaining and terminating the point-to-point link. • Network Control Protocol - provides interaction with different Network layer protocols.

  29. 7.2.2 HDLC and PPP • Link Control Protocol negotiates: • Authentication – PAP and CHAP • compression • error detection • multilink • PPP callback

  30. 7.2.2 HDLC and PPP • Phases of PPP sessions: • Link-establishment - Receipt of the configuration acknowledgement frame completes this phase • Authentication (optional) - provides password protection to identify connecting routers • NCP negotiation - The show interfaces command reveals the LCP and NCP states.

  31. Activity 7.2.2.5

  32. Activity 7.2.2.5

  33. 7.2.3 Configuring PPP • Change encapsulation from HDLC to PPP on both ends of link • Configure desired optional features • ppp multilink • Configures load balancing across multiple links.

  34. 7.2.3 Configuring PPP Verification and troubleshooting commands: • show interfaces serial - Displays the encapsulation and the states of the Link Control Protocol (LCP). • show controllers - Indicates the state of the interface channels and whether a cable is attached to the interface • debug serial interface - Verifies the incrementation of keepalive packets. • debug ppp - Provides information about the various stages of the PPP process, including negotiation and authentication

  35. 7.2.3.3 Configuring PPP

  36. 7.2.4 PPP Authentication • Occurs after establishment of the link but before the Network Layer protocol configuration • Password Authentication Protocol (PAP) • PAP sends the username/password pair across the link repeatedly in clear text

  37. 7.2.4 PPP Authentication • Challenge Authentication Protocol (CHAP) • uses a three-way handshake. • PPP establishes the link phase. • Local router sends a challenge message to the remote router. • 3. Remote router uses the challenge and a shared secret password to generate a one-way hash. • 4. Remote router sends back one-way hash to the local router. • 5. Local router checks the response against its own calculation, using the challenge and the same shared secret. • 6. Local router acknowledges authentication if values match. • 7. Local router immediately terminates connection if the values do not match.

  38. 7.2.4 PPP Authentication

  39. 7.2.4 PPP Authentication

  40. 7.2.5.3 LAB – Configuring PAP and CHAP

  41. Describe Frame Relay • Nonbroadcast multiaccess network • Packet switching with variable length packets • STDM • Virtual circuit between two DTE devices

  42. Describe Frame Relay • Data link connection identifier (DLCI) • Inverse ARP • LMI

  43. Describe Frame Relay Service parameters: • Committed information rate (CIR) • Excess information rate (EIR) • Discard eligible (DE) frames

  44. Describe Frame Relay Traffic management: • Forward explicit congestion notification (FECN) • Backward explicit congestion notification (BECN)

  45. Summary • Circuit switching WAN technologies create a physical circuit between end devices before sending data • Packet and cell switching WAN technologies use virtual circuits to send data across the network • Layer 2 encapsulation changes as frames move across a WAN • PPP permits many advanced features including authentication, compression, and load balancing • Frame Relay is a packet switched technology using switched or permanent virtual circuits • Frame Relay uses parameters such as CIR to establish the bandwidth used on each VC

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