Frame Relay, PPP, and WAN Essentials

Posted on Nov 28, 2024 in Computers

Frame Relay Essentials

Configuration

Where is Frame Relay set? From the line interface of Cisco IOS Command Line Interface (CLI).

Tasks to configure Frame Relay-enabled encapsulation:

  • Configure Frame Relay encapsulation on an interface.
  • Configure dynamic or static assignment of addresses.

Optional tasks for Frame Relay configuration:

  • Set LMI (Local Management Interface).

What command serves Frame Relay SVC encapsulation? encapsulation frame-relay

What command serves bandwidth configuration? bandwidth (Establishes interface bandwidth connection between two systems or devices.)

What is a subinterface? One of the virtual interfaces at one connecting interface physics.

What is DLCI? Data Link Connection Identifier.

Command to set the local DLCI on the subinterface: frame-relay interface-dlci

Command to review Frame Relay configuration: show frame-relay over the desired serial interface.

What does the command debug frame-relay lmi do? Determines if the router and switch Frame Relay LMI packets are sent and received correctly.

Key Concepts

Most popular WAN technology: Frame Relay

Simple Frame Relay WAN topology: Star

Address assignment depending on Inverse ARP: Dynamic

Engineer who invented international Sprint Frame Relay: Eric Scace

Connection through a Frame Relay network between two DTEs: Virtual Circuit

Protocol resolving Layer 3 addresses: ARP

Address assignment where the user chooses direction: Static

Frame Relay benefits: Reduces costs, uses less equipment, less complexity, and easier implementation.

Point-to-Point Protocol (PPP)

What is PPP? Used to connect non-Cisco routers to devices requiring Cisco PPP encapsulation.

PPP components: HDLC, Protocol Control Protocol, Link-NEC Network Control Protocols.

PPP authentication options: PAP or CHAP authentication, Stacker or Predictor compression, Multilink (combines channels to increase WAN bandwidth).

Fields in a PPP frame: Pointing, Direction, Control, Protocol, Data, FCS.

Three phases at a DPI setting section:

  1. Establishment liaison and configuration negotiation.
  2. Determination of the quality of enlacefase.
  3. Negotiation of the network layer protocol configuration.

WAN Access Standards

What describes WAN access standards? Physical layer delivery methods and data link layer requirements (physical address, flow control, encapsulation).

What do data link layer protocols do? Define data encapsulation for remote transmission and resulting frame transfer mechanisms.

What is the point of demarcation? Point separating customer equipment from service provider equipment.

What is the local loop? Copper telephone wire or fiber connecting CPE to the service provider’s CO.

WAN devices: Router, switch, WAN, access server, CSU/DSU, modem.

Data link layer requirement for WAN protocols: Establishing the link via the communication line from sending to receiving device.

WAN switching types:

  • Circuit switching: Establishes a dedicated circuit between nodes before communication.
  • Packet switching: Divides traffic data into packets sent through a shared network.

What is clock bias? Incorrect assumption that all 8 bits sent simultaneously arrive at the same time.

What is Time Division Multiplexing (TDM)? Divides bandwidth into separate channels or time periods.

What is DTE and DCE? DTE (Data Terminal Equipment) is the client, DCE (Data Circuit-terminating Equipment) is the server.

HDLC: Default encapsulation on point-to-point, dedicated, and circuit-switched connections.

PPP: Provides router-to-router and router-to-host connections via synchronous and asynchronous circuits.

PPP functionality: Works with several network layer protocols (IP, IPX).

Steps to enable HDLC encapsulation:

  1. Enter interface configuration mode for the serial interface.
  2. Enter the encapsulation hdlc command.

What is PAP? Password Authentication Protocol.

Why is PAP not secure? Passwords are sent in clear text.

What is CHAP? Challenge Handshake Authentication Protocol.

Why is CHAP more secure? Periodically verifies the remote node’s identity.

Why is authentication important? Prevents security risks on serial connections.

Command to verify interface configuration: show interface

Command to debug PPP authentication: debug ppp authentication

When is PAP used? When CHAP is not supported or a simple text password is required.

WAN Links

Private WAN link options: Dedicated and switched.

Switched links: Point-to-point lines with varying capabilities.

Packet switching data transmission: Labeled frames, cells, or packets.

Public WAN connections: General internet connections.

Leased line: More expensive connections with varying capacities based on bandwidth and distance.

LCP options: Authentication, understanding, stop errors.

Command to enable PPP encapsulation on serial 0/0: r3(config-if)# encapsulation ppp

Command to configure PPP compression: r3(config-if)# compress [predictor | stac]

Command to verify PPP encapsulation: show interfaces serial

Troubleshooting command: debug (accessed from privileged EXEC mode).