WANs and Routers

1
WANs and Routers

• Joanne Wagner
• CCNP, CCAI, Security, CCSP

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WAN OVERVIEW

• Used to connect LANs that are separated by a
  large geographic area
• WAN protocols differ from LAN protocols mostly at
  the OSI Physical and Data Link Layers

3
The figure shows the relationship between the
common WAN technologies and the OSI model
4
WAN CHARACTERISTICS

• Uses the services of Regional Bell Operating
  Companies (RBOC) for operational and functional
  connections
• Unlike LANs, uses serial interfaces operating at
  lower speeds

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WAN Line Types/Bandwidth
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WAN Devices

• WAN Devices include
• Routers
• Router offer many services, including
  internetworking and WAN interface ports.
• Switches
• Switch in the WAN provide connectivity for voice,
  data, and video communication.
• Modems
• Include interface voice-grade services,
• channel service units/digital service units
  (CSU/DSUs) that interface T1/E1 services,
• Terminal Adapters/Network Termination 1 (TA/NT1s)
  
• Communication servers
• Concentrate dial-in/dial-out user communication.

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Introduction to WANs

• Organizations who provide us with most of our WAN
  standards and protocols
• International Telecommunications Union (ITU)
• International Organization for Standards (ISO)
• Internet Engineering Task Force (IETF)
• Electronic Industries Association (EIA)

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WANs Physical Layer

• DTE (Data Terminal Equipment) is the device at
  the user end of a user-network interface that
  serves as a data source, destination, or both.
• DTE connects to a data network through a DCE
  device and typically uses clocking signals
  generated by the DCE.
• DTE includes such devices as routers, computers,
  protocol translators, and multiplexers.

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WANs Physical Layer

• DCE - Data communications equipment (EIA
  expansion) or data circuit-terminating equipment
  (ITU-T expansion).
• The DCE provides a physical connection to the
  network, forwards traffic, and provides a
  clocking signal used to synchronize data
  transmission between DCE and DTE devices. Ex
  Modems and CSU/DSUs

Hint Use router show controller serial 0/0 to
find out if a cable is a DTE or a DCE
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WAN Physical Layer Standards

• EIA/TIA-232
• EIA/TIA-449
• V.24
• V.35
• X.21
• ISDN
• T1,T3, E1 and E3
• SONET (OC-3, OC-12, OC-48, OC-192)

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WANs DATA LINK LAYER

• Define how frames are carried between systems on
  a single data link
• High-Level Data Link Control (HDLC)
• Frame Relay
• LAPF
• Point-to-Point (PPP)
• Integrated Services Digital Network (ISDN)
• LAPD
• LAPB
• X.25

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WAN Data Link Protocols HDLC

• The Cisco default serial line encapsulation type.
  
• It is used when communicating with another Cisco
  device.
• If communicating with a non-Cisco device,
  synchronous PPP is a viable option.
• HDLC is normally proprietary between vendors.
  There is no windowing or flow control.

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WAN DATA LINK PROTOCOLS PPP

• Provides router-to-router (LAN to LAN) and
  host-to-network connections over synchronous and
  asynchronous circuits
• Standardized so it supports vendor
  interoperability
• Contains a protocol field to identify the network
  protocol

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WAN DATA LINK PROTOCOLS PPP

• The Point-to-Point Protocol (PPP) is a standard
  serial line encapsulation method which includes
• Protocol type field
• Link Control Protocol - This protocol can, among
  other things, check for link quality during
  connection establishment.
• Support for authentication through the Password
  Authentication Protocol (PAP) and the Challenge
  Handshake Authentication Protocol (CHAP)

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Comparing WAN Frame Encapsulation Formats
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DATA LINK PROTOCOLS ISDN

• A digital circuit-switched service that transmits
  voice and data over existing telephone lines
• ISDN applications include high-speed image
  applications, high-speed file transfer, video
  conferencing, and voice service

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DATA LINK PROTOCOLS ISDN

• ISDN services
• Basic Rate Interface (BRI)
• Operates over most copper twisted-pair telephone
  wiring in place today.
• Delivers a total bandwidth of a 144-kbps line
  into three separate channels.
• Primary Rate Interface (PRI)

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• ISDN BRI
• Two of the channels, called B (bearer) channels,
  operate at 64 kbps and are used to carry voice or
  data traffic.
• The third channel, the D (data) channel, is a
  16-kbps signaling channel used to carry
  instructions that tell the telephone network how
  to handle each of the B channels.
• Often referred to as 2BD.

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DATA LINK LAYER PROTOCOLS FRAME RELAY

• Uses high quality digital facilities with no
  error correction
• More efficient than X.25
• A packet-switched technology that enables end
  stations to dynamically share the network medium
  and the available bandwidth

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DATA LINK LAYER PROTOCOLS FRAME RELAY

• Frame Relay
• Designed with higher speed.
• As a result, Frame Relay contains a limited
  amount of error checking and reliability
  features.
• Upper-layer protocols are expected to attend to
  these issues.
• Most common packet-switched network type

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WAN CONNECTION TYPES
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WAN PROTOCOLS
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Connection Type Dedicated (Leased)

• Dedicated connectivity, also referred to as
  leased lines, provides full-time synchronous
  connections.
• Dedicated, full-time connectivity is provided by
  point-to-point serial links.
• The cost of dedicated line solutions can become
  significant when deployed to connect many sites,
  which is especially true if full meshing is
  desired.

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Connection Type Dedicated (Leased)

• Leased lines of this type are ideal for
  high-volume environments with a steady-rate
  traffic pattern.
• Use of available bandwidth is a concern because
  the cost of the line is paid even when the
  connection is idle.

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Connection Type Dedicated (Leased)
T1 is a dedicated WAN technology
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Connection Type Dedicated(Leased)
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Dedicated leased lines are a reasonable design
option for the core WAN
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Connection Type Circuit-Switched

• Used primarily to
• connect remote users
• mobile users to corporate LANs.
• backup lines for higher-speed circuits, such as
  Frame Relay and dedicated lines.

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Connection Type Circuit-Switched

• brought up when needed
• generally low bandwidth
• Basic Telephone Service connections are generally
  limited to 28.8 kbps without compression, ISDN to
  64 or 128 kbps.

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Connection Type Circuit-Switched

• There are two ISDN services
• Basic Rate Interface (BRI)
• Primary Rate Interface (PRI)
• ISDN BRI
• operates over most of the copper twisted-pair
  telephone wiring in place today.
• delivers a total bandwidth of a 144-kbps line
  into three separate channels.

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Connection Type Circuit-Switched

• ISDN provides great flexibility to the network
  designer because of its ability to use each of
  the B channels for separate voice or data
  applications
• Example, a long document can be downloaded from
  the corporate network over one ISDN 64-kbps B
  channel while the other B channel is being used
  to connect to browse a World Wide Web page.
• Care should be taken in the design phase to
  ensure that the equipment selected has the
  feature set that takes advantage of ISDNs
  flexibility.

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Connection Type Frame Relay

• Information contained in packets or frames
• Shares non-dedicated bandwidth with other WAN
  subscribers' frames.
• A WAN switch forwards Frame Relay and X.25
  traffic.

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Connection Type Frame Relay

• X.25 can use Switched Virtual Circuits (SVCs),
  with some initial delay for call setup, or
  Permanent Virtual Circuits (PVCs) which avoid
  delays for call setup.
• Frame Relay uses Layer 2 identifiers and
  Permanent Virtual Circuits (PVCs).

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Connection Type Frame Relay

• Frame Relay defines the connection between a
  customer DTE and a carrier DCE.
• The DTE is typically a router or FRAD (Frame
  Relay access devices)
• The DCE is a Frame Relay switch.
• Frame Relay access is at
• 56 kbps, 64 kbps, or 1.544 Mbps

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Frame Relay Cost Effective
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A packet switched line is used to share a single
point-to-point link to transport packets.
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WAN CONNECTION TYPESSUMMARY
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WAN PROTOCOLSSUMMARY
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WAN TECHNOLOGYSUMMARY
WAN link options are classified as dedicated and
switched
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ROUTER OVERVIEW
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Internal Configuration Components
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WANs The Router

• A router is a special type of computer. It has
• CPU
• memory,
• a system bus,
• various input/output interfaces.
• Routers are designed to perform some very
  specific functions.
• routers connect and allow communication between
  two networks and determine the best path for data
  to travel through the connected networks.

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WANs The Router

• A Routers Requires
• Internetwork Operating System software (IOS)
• CPU
• Configuration file

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Introduction to routers in a WAN

• The main internal components of the router are
• Random access memory (RAM),
• Stores routing tables
• Holds ARP cache
• Holds fast-switching cache
• Performs packet buffering (shared RAM)
• Maintains packet-hold queues
• Provides temporary memory for the configuration
  file while the router is powered on (stores
  running configuration file)
• Loses content when router is powered down or
  restarted
• Nonvolatile random-access memory (NVRAM),
• Provides storage for the startup configuration
  file which
• contains the instructions that a router uses
  to control the flow of traffic through its
  interfaces
• Retains content when router is powered down,
  restarted, or power is lost.

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Introduction to routers in a WAN

• The main internal components (continued)
• Flash memory,
• Holds or stores the Cisco operating system image
  (IOS)
• Allows software to be updated without removing
  and replacing chips on the processor
• Retains content when router is powered down or
  restarted
• Can store multiple versions of IOS software
• Is a type of electronically erasable,
  programmable ROM (EEPROM)
• Read-only memory (ROM), and
• Maintains instructions for power-on self test
  (POST) diagnostics
• Stores bootstrap program and basic operating
  system software
• Requires replacing pluggable chips on the
  motherboard for software upgrades
• Interfaces.
• Network connection through which packets enter
  and leave the router
• Connect router to network for frame entry and
  exit
• Can be on the motherboard or on a separate module
  
• Connects the router to LANs and WANs

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Router LANs and WANs

• Routers have both LAN and WAN interfaces.
• While a router can be used to segment LANs, its
  major use is as a WAN device.
• Routers are the backbone devices of large
  intranets and of the Internet.
• They operate at Layer 3 of the OSI model, making
  decisions based on network addresses.
• The two main functions of a router are
• the selection of best path for and
• the switching of frames to the proper interface.
• Routers accomplish this by building routing
  tables and exchanging network information with
  other routers.

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Router LANs and WANs (cont.)

• An administrator can maintain routing tables by
• configuring static routes,
• but generally routing tables are maintained
  dynamically through the use of a routing protocol
  that exchanges network topology (path)
  information with other routers.
• A correctly configured internetwork provides the
  following
• Consistent end-to-end addressing
• Addresses that represent network topologies
• Best path selection
• Dynamic or static routing
• Switching

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Router internal components

• CPU
• RAM
• Flash
• NVRAM

• Buses
• ROM
• Interfaces
• Power Supply

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Router internal components

• CPU The Central Processing Unit (CPU) executes
  instructions in the operating system.
• RAM Random-access memory (RAM) is used for
  routing table information, fast switching cache,
  running configuration, and packet queues.
• RAM provides run time space for executable Cisco
  IOS software and its subsystems.
• RAM is usually logically divided into main
  processor memory and shared input/output (I/O)
  memory.
• Shared I/O memory is shared among interfaces for
  temporary storage of packets. The contents of RAM
  are lost when power is removed.
• RAM is generally dynamic random-access memory
  (DRAM) and can be upgraded by adding additional
  Dual In-Line Memory Modules (DIMMs).

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Router internal components (cont.)

• Flash Flash memory is used for storage of a
  full Cisco IOS software image.
• The router normally acquires the default IOS from
  flash.
• These images can be upgraded by loading a new
  image into flash.
• The IOS may be in uncompressed or compressed
  form.
• In most routers an executable copy of the IOS is
  transferred to RAM during the boot process.
• In other routers the IOS may be run directly from
  flash.
• Adding or replacing the flash Single In-Line
  Memory Modules (SIMMs) or PCMCIA cards can
  upgrade the amount of flash.

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Router internal components (cont.)

• NVRAM Nonvolatile random-access memory (NVRAM)
  is used to store the startup configuration.
• In some devices, NVRAM is implemented using
  separate electronically erasable programmable
  read-only memory (EEPROMs) in some devices.
• In other devices it is implemented in the same
  flash device from which the boot code is loaded.
• In either case these devices retain contents when
  power is removed.
• Buses Most routers contain a system bus and a
  CPU bus.
• The system bus is used for communication between
  the CPU and the interfaces and/or expansion
  slots. This bus transfers the packets to and from
  the interfaces.
• The CPU bus is used by the CPU for accessing
  components from router storage. This bus
  transfers instructions and data to or from
  specified memory addresses.

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Router internal components (cont.)
Router internal components (cont.)

• ROM Read-only memory (ROM) is used for
  permanently storing startup diagnostic code (ROM
  Monitor).
• The main tasks for ROM are hardware diagnostics
  during router bootup and loading the Cisco IOS
  software from flash to RAM.
• Some routers also have a scaled down version of
  the IOS that can be used as an alternative boot
  source.
• ROMs are not erasable. They can only be upgraded
  by replacing the ROM chips in the sockets.
• Power Supply The power supply provides the
  necessary power to operate the internal
  components.
• Larger routers may use multiple or modular power
  supplies.
• In some of the smaller routers the power supply
  may be external to the router.

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Router internal components (cont.)

• Interfaces The interfaces are the router
  connections to the outside.
• The three types of interfaces are
• local-area network (LANs),
• The LAN interfaces are usually either Ethernet or
  Token Ring.
• These interfaces have controller chips that
  provide the logic for connecting the system to
  the media.
• The LAN interfaces may be a fixed configuration
  or modular.
• wide-area network (WANs),
• The WAN interfaces include serial, ISDN, and
  integrated Channel Service Unit (CSUs).
• As with LAN interfaces, WAN interfaces also have
  special controller chips for the interfaces.
• The WAN interfaces may be a fixed configuration
  or modular.
• Console/AUX.
• The Console/AUX ports are serial ports used
  primarily for the initial configuration of the
  router.
• These ports are not networking ports.
• They are used for terminal sessions from the
  communication ports on the computer or through a
  modem.

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Router physical characteristics

• It is not critical to know the location of the
  physical components inside the router to
  understand how to use the router.
• However in some situations, such as adding
  memory, it can be very helpful.
• The exact components used and their location
  varies between router models. Figure identifies
  the internal components of a 2600 router.
• Figure shows some of the external connectors on
  a 2600 router.

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Router external connections

• The three basic types of connections on a router
  are LAN interfaces, WAN interfaces, and
  management ports.
• LAN interfaces
• LAN interface allow the router to connect to the
  Local Area Network media. This is usually some
  form of Ethernet.
• However, it could be Token Ring or Asynchronous
  Transfer Mode (ATM).
• WAN interfaces
• Wide Area Network connections provide connections
  through a service provider to a distant site or
  to the Internet.
• These may be serial connections or any number of
  other WAN interfaces.
• With some types of WAN interfaces, an external
  device such as a CSU is required to connect the
  router to the local connection of the service
  provider.
• Management interfaces
• The management port provides a text-based
  connection for the configuring, monitoring and
  troubleshooting of the router.
• The common management interfaces are the console
  and auxiliary ports. These are EIA-232
  asynchronous serial ports.

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Management port connections

• The console port and the auxiliary (AUX) port are
  management ports. These asynchronous serial ports
  are not designed as networking ports.
• One of these two ports is required for the
  initial configuration of the router. The console
  port is recommended for this initial
  configuration.
• When the router is first put into service, there
  are no networking parameters configured.
• To prepare for initial startup and configuration,
  attach an RS-232 ASCII terminal, or a computer
  emulating an ASCII terminal, to the system
  console port.
• Then configuration commands can be entered to set
  up the router.
• Not all routers have an auxiliary port.

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Management port connections

• Once this initial configuration is entered into
  the router through the console or auxiliary port,
  the router can then be connected to the network
  for troubleshooting or monitoring.
• The router can also be configured from a remote
  location by dialing to a modem connected to the
  console or auxiliary port on the router.
• The console port is also preferred over the
  auxiliary port for troubleshooting.
• This is because it displays router startup,
  debugging, and error messages by default.
• The console port can also be used when the
  networking services have not been started or have
  failed.
• Therefore, the console port can be used for
  disaster and password recovery procedures.

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Connecting console interfaces

• To connect to the console port, a rollover cable
  and a RJ-45 to DB-9 adapter are used to connect a
  PC.
• Cisco supplies the necessary adapter to connect
  to the console port.
• The PC or terminal must support VT100 terminal
  emulation. Terminal emulation software such as
  HyperTerminal is usually used.
• To connect the PC to a router
• Configure terminal emulation software on the PC
  for
• The appropriate com port
• 9600 baud
• 8 data bits
• No parity
• 1 stop bit
• No flow control
• Connect the RJ-45 connector of the rollover cable
  to the router console port.
• Connect the other end of the rollover cable to
  the RJ-45 to DB-9 adapter.
• Attach the female DB-9 adapter to a PC.

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Connecting console interfaces
When connected using the console interface, the
computer is acting as a dumb terminal.
ltRouter Outputgt
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Connecting console interfaces
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Connecting console interfaces
ltRouter Outputgt
ltRouter Outputgt
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Connection LAN interfaces

• In most LAN environments, the router is connected
  to the LAN using an Ethernet or Fast Ethernet
  interface.
• The router is a host that communicates with the
  LAN via a hub or a switch. A straight-through
  cable is used to make this connection.
• A 10/100BaseTX router interface requires Category
  5 or better, unshielded twisted-pair (UTP)
  regardless of the router type.
• In some cases the Ethernet connection of the
  router is connected directly to the computer or
  to another router. For this type of connection, a
  crossover cable is required.

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Connecting WAN interfaces (cont.)

• Perhaps the most commonly used router interfaces
  for WAN services are serial interfaces. Selecting
  the proper serial cable is as easy as knowing the
  answers to four questions
• What is the type of connection to the Cisco
  device?
• The interface on the left is a Smart Serial
  interface.
• The interface on the right is a DB-60 connection.
  
• Is the network system being connected to a DTE or
  DCE device?
• DTE and DCE are the two types of serial
  interfaces that devices use to communicate.
• The key difference between these two is that the
  DCE device provides the clock signal for the
  communications on the bus.
• What signaling standard does the device require?
  
• For each different device, a different serial
  standard could be used. Each standard defines the
  signals on the cable and specifies the connector
  at the end of the cable.
• Is a male or female connector required on the
  cable?
• If the connector has visible projecting pins, it
  is male.
• If the connector has sockets for projecting pins,
  it is female.

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Points to Remember

• WANS operate over large geographic areas
• WAN protocols and standards differ from LAN
  protocols mostly at the Physical and Data Link
  Layer of the OSI Model
• WANS use routers, switches, modems, and
  communication servers
• Console and/or Auxiliary ports on the router are
  used for initial configuration
• The Console port is used for debugging, password
  recovery, and troubleshooting
• Terminal emulation software (hyper terminal) is
  used to establish the connection between the
  router and PC for initial configuration
• To establish a connection between the PC and
  router use a rollover cable, DB-9 connector and
  a RJ-45 connector

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Points to Remember (cont)

• Management connections are non-network
  connections, are used for initial
  configuration, and are asynchronous serial ports.
• Management connections are used for
  troubleshooting problems and monitoring the
  system
• RAM stores routing tables, holds fast switching
  cache, stores the running configuration, holds
  ARP cache, and is lost when power is shut down
• NVRAM stores the startup configuration and
  retains contents when powered down
• FLASH memory stores the IOS software images. It
  may need to have memory added to hold multiple
  versions of the image
• Interfaces connect the router to the network,
  connect LANs and WANs, and use the configuration
  files to control the flow of traffic through the
  interfaces