Wide Area Network(WAN)

In preparation of your CCNA exam, we want to make sure we cover the various concepts that we could see on your Cisco CCNA exam. So to assist you, below we provided a CCNA WAN Concepts Cliff Notes article. This section will probably be most helpful to review immediately before you take your Cisco CCNA certification exam on test day!

Your Cisco CCNA exam is going to hit you very hard on WANs. This may be one of the most difficult concepts to recreate in your lab as you prepare for your Cisco CCNA exam. Most people cannot afford the thousands of dollars it would cost to recreate every WAN technology that is covered on your Cisco CCNA exam. But don’t worry, we will cover a majority of the terms below and with a well thought out home CCNA lab, you will be well on your way to passing your Cisco CCNA exam!

There are two major types of networks: LAN(local area networks) and WANs(Wide Area Networks). A WAN is a network that spans geographic areas and includes technologies such as leased lines, Frame Relay and ATM. Your Cisco router will support all of these WAN technologies and more. You will lease the lines from your local telco or service provider.

WAN Terms
Customer Premises Equipment(CPE): Equipment that are owned and located at the customer's premises. This can include your Cisco router and CDU/DSU.
Demarcation (demarc): Service provider connection to the customer's premises. Usually an RJ-45 connection that plugs into the customer's CSU/DSU or ISDN interface.
Local Loop: A line that connects a customer's demarc to the closest Service Provider's Central Office (CO).
Central Office (CO) or Point of Presence(POP): Connects customers to the Service Provider's switching network.

WAN Connection Type
Leased or Dedicated Line:

  • Permanent connection between two CPEs through the Service Provider's switched network. It allows DTE devices(Cisco routers are DTE devices) to communicate without connection setup .
  • Uses Synchronous Serial line with speed up to 45 Mbps

    Circuit Switching.

  • Requires connection setup before transmitting data.
  • Uses Asynchronous Serial (dial up modem) and ISDN.
  • Offers low bandwidth data transfer.

    Packet Switching:

  • Uses Frame Relay and X.25
  • Offers Shared bandwidth between Customers
  • Speed ranges from 56 Kbps to 2.048 Mbps.

    WAN Technologies
    LAPB (Link Access Procedure Balanced)

  • Connection-Oriented at the Data-Link layer for use with X.25. It has high overhead and is used for error prone connections.

    Frame Relay

  • Connection Oriented. Works in the Data Link and Physical Layers and supports wide variety of network protocols.
  • Provides higher performance and more cost effective links than X.25 because it assumes that error checking will occur at higher layers. Speed ranges from 64Kbps to 1.544Mbps.
  • Frame Relay allows two DTE devices to communicate through DCE devices. Frame Relay also supports dynamic-bandwidth allocation and Congestion Control.
    DTE (Data Terminal Equipment): Consists of terminals, PCs, Cisco Routers, and bridges.
  • DCE (Data Circuit-terminating Equipment): Consists of carrier-owned internetworking devices.

    Congestion Control:

  • DE (Discard Eligibility): A bit in the frame relay packet header, when set and congestion occurs the frame will be dropped.
  • FECN (Forward-Explicit Congestion Notification): Sent to the destination router by the frame relay switch indicating congestion.
  • BECN (Backward-Explicit Congestion Notification): Sent to the source router by the frame relay switch telling it to slow down data transmission rate.
  • Subscribers usually buy less than the bandwidth they may need from the service provider, this is called CIR (Committed Information Rate.) If data rate exceeds customer's CIR, packets will still be transmitted but it will be marked for Discard Eligibility (DE.)
  • Frame Relay Uses virtual circuits PVC and SVC to create logical connections between DTE devices.
  • Frame Relay is NonBroadcast MultiAccess (NBMA), this mean it will not forward broadcasts by default. DLCl (Data Link Connection Identifier): Used to identify the virtual circuits (PVCs) created between DTE devices.
  • Each IP address of a remote router is mapped to a local DLC number (ranges 16 to 1007) dynamically using IARP (Inverse ARP) or manually using “map” statement.

    Frame Relay encapsulation types:
    1- Cisco (default), Cisco proprietary.
    2- IETF, standards- Frame Relay and Sub-Interfaces:

  • Solves Split Horizon problem; route updates received on subinterface will be advertised out of 2nd subinterface.
  • Solves Frame Relay's costly full mesh requirement.

    LMI(Local Management Interface):

  • LMI is the signaling standards between the CPE devices and the frame-relay switch.
  • LMI messages provides the following info: Keepalives, Multicasting, Multicast addressing and Status of virtual circuits.
  • A router receives LMI that updates the virtual circuit status to one of the following three states;
    Active state: Connection established, exchange data.
    Inactive state: Remote router is not working.
    Deleted slate: No LMI information is being received on the int.

    LMI Types:
    1 – Cisco (default)
    2- ANSI (ANSI T1.617 standards
    3- Q93$A (ITU-T standards)
    HDLC (High-Level Data Link Control)

  • Low overhead Connection-Oriented at the Data-Link Layer.
  • HDLC is point-to-point protocol used on leased lines.
  • HDLC is bit-Oriented protocol which uses a single bit, as opposed to Byte-Oriented protocols which uses entire byte, to represent control information). HDLC is Cisco's default encapsulation.
  • Standard HDLC was not intended to encapsulate multiple network layer protocols {i.e. IP & IPX) on the same link.
  • Each vendor has their own way of identifying network layer protocol, usually by inserting proprietary field in the standard HDLC frame, which makes it proprietary to their equipment.
  • HDLC does not support authentication. PPP(Point-to-Point Protocol)
  • Runs over Synchronous (ISDN) and Asynchronous (dial-up) links. PPP is the industry standard. It is used to create point-to-point links between different vendors' equipment.
  • PPP works only at the Data-Link and Physical layer.
  • It uses Network Control Protocol (NCP) to identify the Network layer protocol (i.e. IP, IPX and AppleTalk).
  • Supports Authentication and multilink connection. Three connections phases for PPP link: Link Establishment Phase: LCP packet is sent. It contains configuration options (i.e. data, compression & authentication). Authentication Phase: Either CHAP or PAP if configured.
  • Password authentication Protocol: Less secure than CHAP. Password is sent in text. Authentication is done only at link initiation.
  • Challenge Authentication Protocol, CHAP: Authentication is performed periodically. More secure than PAP. Uses MD5 for encryption.

    Network Layer Protocol Phase: Allows multiple Network layer protocols to be encapsulated and sent over a PPP link. PPP main components: E1A/TIA-232-C: A Physical layer international standard for serial connection.
    HDLC: Used to encapsulate datagrams over serial links. Network Control Protocol (NCP): Used to identify the Network layer protocol (i.e. IP, IPX, AppleTalk).
    Link Control Protocol (LCP): Supports authentication, compression, error detection and multilink.

    Configuring PPP:
    Router(config-if)# encapsulation ppp Enable PPP on an int.

    How to configure Authentication between Cisco Routers
    Assign a host name to the router.
    Router(config}# hostname New York

    Remote router name and password are defined
    New York(config}# username RouterA password cisco

    Configure the remote router’s name and password
    RouterA(config)# username New York password cisco

    Configure an authentication type.
    RouterA(config)# ppp authentication (chap I pap)

    Synchronous Optical Network (SONET)

  • SONET is a Layer-1 standard for using fiber optics for telecommunications transmissions. SONET link speed:
    52 Mbps (OC-1) 155 Mbps (OC-3)
    622 Mbps (OC-12) 2.4 Gbps (OC-48)
    9.6 Gbps (OC-192) 40 Gbps (OC-768)

    Asynchronous Transfer Mode (ATM)

  • Is the data-link layer (L2) services that run over SONET.
  • ATM is capable of transferring voice and data traffic on the same link. ATM uses Cells rather than Frames.
  • Cells are fixed in size (53 bytes, 48 bytes in payload and 5 bytes in header).
  • Cell header consist of; 1. Virtual Path Identifier (VPI). 2. Virtual Channel Identifier (VCI), which are used to forward cells.
  • Routers that support ATM interface are capable of converting Ethernet frames into Cells. In the conversion process, ethernet frames are segmented into cells then they are forwarded to the ATM network. This process is reversed when cells enter the ethernet network.

    DSL Protocols
    New to the Cisco CCNA exam is DSL concepts. So we will touch on a few of the DSL protocols that you may see on the exam below. 1. ATM at Layer-2; between the DSL router and the ISP router.
    2. Point-to-Point over ATM (PPPoA) at Layer-2; PPP is used for IP address assignment and authentication.
    3. Point-to-Point over Ethernet (PPPoE) at Layer-2; used between PC to DSL-modem Ethernet connection.

    I hope you found this article to be of use and it helps you prepare for your Cisco CCNA certification. Achieving your CCNA certification is much more than just memorizing Cisco exam material. It is having the real world knowledge to configure your Cisco equipment and be able to methodically troubleshoot Cisco issues. So I encourage you to continue in your studies for your CCNA exam certification.