© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 1 Implementing Enterprise WAN Links Introducing Routing and Switching in the Enterprise – Chapter 7

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 2 Objectives  Describe the features and benefits of common WAN connectivity options.  Compare and configure common WAN encapsulations.  Describe Frame Relay

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public WAN Devices and Technology  WAN Services purchased  Serial transmissions verses Ethernet in LANS

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 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

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 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

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public WAN Devices and Technology Note: DS0 – Digital Signal 0, T1 (DS1) = 24 DS0s

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 7 Activity

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 8 Activity

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public WAN Standards Layer 2 WAN protocols:  LAPF  HDLC  PPP

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public WAN Standards Activity

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public WAN Standards Activity

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 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

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 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

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 14 Activity

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 15 Activity

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public Packet and Circuit Switching  Dedicated Leased Line – point-to-point serial  Circuit switching: Dedicated bandwidth Higher cost Higher level of security

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 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

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 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)

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public Last mile and long range WAN technologies

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public Last mile and long range WAN technologies  Elements of Layer 2 encapsulations Flag Address Control Protocol Data FCS

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 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

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 22 Activity

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 23 Activity

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 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

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 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

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 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

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 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)

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 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.

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public HDLC and PPP  Link Control Protocol negotiates: Authentication – PAP and CHAP compression error detection multilink PPP callback

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 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.

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 31 Activity

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 32 Activity

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 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.

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 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

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 35

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 36

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public Configuring PPP

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 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

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public PPP Authentication  Challenge Authentication Protocol (CHAP) uses a three-way handshake. 1.PPP establishes the link phase. 2.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.

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public PPP Authentication

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public PPP Authentication

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public LAB – Configuring PAP and CHAP

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 43 Describe Frame Relay  Nonbroadcast multiaccess network  Packet switching with variable length packets  STDM  Virtual circuit between two DTE devices

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 44 Describe Frame Relay  Data link connection identifier (DLCI)  Inverse ARP  LMI

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 45 Describe Frame Relay Service parameters:  Committed information rate (CIR)  Excess information rate (EIR)  Discard eligible (DE) frames

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 46 Describe Frame Relay Traffic management:  Forward explicit congestion notification (FECN)  Backward explicit congestion notification (BECN)

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 47 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

© 2006 Cisco Systems, Inc. All rights reserved.Cisco Public 48