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CCNA Exploration: Network Fundamentals > Ch 1 - Intro to Routing and Packet Forwarding > Flashcards

Ch 1 - Intro to Routing and Packet Forwarding Flashcards

1
Q

Routers are at the Network Center

  • What does a router do?
A
  • A router connects multiple networks.
    • This means that it has interfaces that belong to different IP networks.
  • When a router receives an IP packet on one interface, it determines which interface to forward the packet on its way to its destination.
    • The interface that the router uses to forward the packet can be the network of the final destination of the packet or it can be a network connected to another router that is used to reach the destination network.
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2
Q

Interfaces

  • LAN and WAN
A
  • Each network that a router connects to typically requires a separate interface.
  • These interfaces are used to connect a combination of both Local-Area Networks (LAN) and Wide-Area Networks (WAN).
  • LANs are commonly Ethernet networks that contain device such as PCs, printers, and servers.
  • WANs are used to connect networks over a large geographical areas.
    • example: WAN connection is commonly used to connect a LAN to the ISP.
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3
Q

Routers Primary Responsibilites

A
  1. Determining the best path to send packets.
  2. Forwarding packet toward their destination.

The router uses its routing table to determine the best path to forward the packet.

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4
Q

Operations of the routing table

A
  • The router uses its routing table to determine the best path to forward the packet.
  • When the router receives a packet, it examines the destination IP address and searches for the best match with a network address in the router’s routing table.
  • The routing table will include the interface to be used to forward the packet.
  • When a match is found, the router encapsulates the IP packet into the data-link frame of the outgoing or exit interface, and the packet is then forwarded toward its destination.
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5
Q

Example: Router Determine the Best Path

A
  1. R1 receives the packet encapsulated in an Ethernet frame.
  2. After decapsulating the packet, the router uses the destination IP address of the packet to search the routing table for a matching network address.
  3. R1 will encapsulate the packet in a frame format appropriate for the outbound interface and then forward the packet.
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6
Q

Router CPU and Memory

A

Similar to a PC, a router also includes:

  • CPI
  • RAM
  • ROM
  • Flash memory
  • NVRAM
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7
Q

Router CPU

A
  • The CPU executes operating system instructions, such as system initialization, routing functions, and network interface control.
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8
Q

Router RAM

  • Operating System
  • Running Config file
  • IP routing table
  • ARP Cache
  • Packet Buffering
A

Similar to computers, RAM stores the instructions and data needed to be executed by the CPU.

RAM is volatile memory and loses its contents when the router is powered down or restarted.

RAM is used to store:

  • OS - Cisco IOS image is copied into RAM during bootup.
    • show version
      • Model
      • IOS Version & software release
      • CPU,

RAM, NVRAM & Flash

    * Configuration Register setting
  • Running Config File - this is the configuration file that stores the configuration commands that the router’s IOS is currently using.
    • show running-config
  • IP Routing Table - This is the file that stores info about directly connected and remote networks.
    • show ip route
  • ARP Cache - this cache stores IP address-to-MAC address mappings, similar to the ARP cache on a PC. ARP cache would be used on routers that have Ethernet interfaces/
  • Packet Buffering - packets are temporarily stored in a buffer when recevied on an interface or before they exit an interface.
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9
Q

Router ROM

  • Bootstrap info
  • Basic Diagnostic software
  • Scaled-down version of IOS
A

ROM uses firmware, which is software embedded inside the integrated circuit.

ROM does not lose its contents when the router loses power or is restarted.

ROM stores:

  • Bootstrap info
  • Basic Diagnostic software
  • Scaled-down version of IOS
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10
Q

Router Flash Memory

A
  • Flash memory is nonvolatile computer memory that can be electrically erased and reprogrammed.
  • Flash memory data does not lose its contents when the router loses power or is restarted.
  • Flash is used as permanent storage for the operating system, Cisco IOS.
  • The IOS is permanently stored in flash memory and copied into RAM during bootup.
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11
Q

Router NVRAM

A
  • Non-Volatile Random-Access-Memory, which does not lose its data when the power is turned off.
  • NVRAM is used as permanent storage for the startup-config file.
  • To save those changes in case the router is restarted or loses power, the running-config must be copied to NVRAM, where it is stored as the startup-config file.
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12
Q

ROUTER BOOT-UP PROCESS

A

There are four major phases to the bootup process:

  1. Perform the POST.
  2. Loading the bootstrap program.
  3. Locating and loading the Cisco IOS software.
  4. Locating and loading the startup config file or entering setup mode.
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13
Q

Perform the POST (power-on self test)

A
  • A common process that occurs on almost every computer during bootup.
  • The POST process is used to test the router hardware.
  • When the router is powered on, software on the ROM chip conducts the POST.
  • During this self-test, the router executes diagnostics from ROM on several hardware components including the CPU, RAM and NVRAM.
  • After the POST has been completed, the router executes the bootstrap program.
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14
Q

Loading the bootstrap program

A
  • After the POST, the bootstrap program is copied from ROM to RAM.
  • Once in RAM, the CPU executes the instructions in the bootstrap program.
  • The main task of the bootstrap program is to locate the Cisco IOS and load it into RAM.

NOTE: At this point, if you have a console connection to the router, you will begin to see output on the screen.

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15
Q

Locating and Loading Cisco IOS

A
  • The IOS is typically stored in flash memory, but can also be stored in other places such a TFTP server.
  • If a full IOS image cannot be located, a scaled-down version of the IOS is copied from ROM into RAM.
  • This version of IOS is used to help diagnose any problems and can be used to load a complete version of the IOS into RAM.
  • Loading IOS, some other Cisco routers ran the IOS directly from flash, but current models copy the IOS into RAM for execution by the CPU.

NOTE: Once the IOS begins to load, you may see a string of pounds signs (#), while the image decompresses.

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16
Q

Locating the Startup Config File

A
  • After the IOS is loaded, the bootstrap program searches for the startup config file in NVRAM.
  • This file has the previously saved config commands and parameters including:
    • Interface addresses
    • Routing information
    • Passwords
    • Any other config saved by the network admin
  • If the startup config file is located in NVRAM, it is copied into RAM as the running-config file.
17
Q

NOTE: If the startup config file does not exist in NVRAM

A

NOTE: If the startup config file does not exist in NVRAM, the router may search for a TFTP server. If the router detects that it has an active link to another configured router, it sends a broadcast searching for a configuration file across the active link. This condition will cause the router to pause, but you will eventually see a console message like:

%Error opening

tftp://255.255.255.255/network-confg (Timed out)

%Error opening

tftp://255.255.255.255/cisconet-confg (Timed out)

18
Q

Executing the Config File

A

If a startup configuration file is found in NVRAM, the IOS loads it into RAM as the running-config and executes the commands in the file, one line at a time.

19
Q

Enter Setup Mode (Optional)

A
  • If the startup configuration file cannot be located, the router prompts the user to enter setup mode.
  • Setup Mode is a series of questions prompting the user for basic config info.
20
Q

show version command

A
  • Information about the version of the Cisco IOS software currently running on the router.
    • Cisco Internetwork Operating System Software

IOS (tm) C2600 Software (C2600-I-M), Version 12.2(28), RELEASE SOFTWARE (fc5)

  • The version of the bootstrap program.
    • ROM: System Bootstrap, Version 12.1(3r)T2, RELEASE SOFTWARE (fc1)
  • Information about the hardware configuration, including the amount of system memory.
    • cisco 2621 (MPC860) processor (revision 0x200) with 60416K/5120K bytes of memory
21
Q

ROUTER INTERFACES

A
  • Management Ports
    • console port
    • aux port
  • Router Interfaces
    • Ethernet port
    • Serial port
22
Q

Management ports

A
  • Physical connectors that are used to manage the router.
  • Not used for packet forwarding.
  • Most common management port is the Console port.
    • The console port is used to connect a terminal, or most often a PC running terminal emulator software, to configure the router without the need for network access to that router.
    • The console port must be used during initial configuration of the router.
  • Another management port is the Aux port.
    • Not all routers have auxiliary ports.
    • At times the auxiliary port can be used in ways similar to a console port. It can also be used to attach a modem.
23
Q

Ethernet ports

A
  • The term interface on routers refers to a physical connector on the router whose main purpose is to receive and forward packets.
  • Routers have multiple interfaces that are used to connect to multiple networks.
  • Interfaces connect to various types of networks, which means that different types of media and connectors are required.
  • Router interfaces can be divided into two major groups:
    • LAN interfaces - such as Ethernet and FastEthernet

.

* WAN interfaces - such as serial, ISDN, and Frame Relay  .

CCNA Exploration: Network Fundamentals (2 decks)

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