Semester 2 Review

1
Semester 2 Review

• Router Configuration

2
Router Components and Configuration

• As you learned earlier, routers are
  internetworking devices that function at the
  Network layer of the OSI model.
• Routers route packets across the best path, among
  multiple available paths.
• Routers do not pass broadcasts and are used in
  many organizations to limit broadcast domains.
• For all their fancy functions, routers are just
  specialized hardware configured with specialized
  software to perform the task of routing packets.

3
Router Components

• Cisco routers are powered by the Cisco
  Internetwork Operating System (IOS). The IOS
  provides the operating system that allows the
  routers to be configured to perform certain
  tasks.
• Since each IOS version may implement a feature in
  a slightly different way, you must be aware of
  what IOS is in use on your routers.
• The show version command displays IOS information
  including the IOS filename and version.

4
Show Version Command Output
5
Router Components Continued

• Following are the router components you must know
  and understand for the CCNA exam
• Random Access MemoryRAM, which holds the
  router's running configuration contents are lost
  when the router is powered down
• Non-Volatile Random Access Memoryspecial RAM
  used to hold the routers startup configuration
  does not lose its contents if powered down
• Flash Memoryrewritable memory used to hold the
  IOS image for the router contents are not lost
  if the router is powered down.
• Read Only Memorythe bootstrap usually contains
  at least a minimal version of the IOS
• Interfaceshardware connectivity points on the
  router aka ports

6
Show Commands for RAM

• The IOS contains show commands to view each of
  the routers components. To view the contents
  and properties of RAM, you can issue several
  commands
• show running-configuration
• show memory
• show buffers
• The show running-configuration command is one of
  the most frequently used commands. It displays
  the working configuration file on the router.

7
Show Run Command Output
8
Show Interfaces Command

• To view the status and types of interfaces on the
  router, use the show interfaces command.
• The show ip interfaces command displays the same
  type of output as the show interfaces command but
  for ip interfaces only.
• Important information such as physical and data
  link layer connectivity issues can be determined
  from these commands.
• These commands are particularly helpful in
  troubleshooting.

9
Show Int Command Output
If the physical layer and data link layer
protocols are up and running, the interface will
be listed as Interface is up, line protocol up.
The configured network layer address is displayed
with this command. A /24 after the IP address
denotes a 24 bit subnet mask or a mask of
255.255.255.0.
This interface is listed as Serial0 is down, line
protocol is down because neither a physical layer
or data link layer connection is active. In this
case, a cable is not connected and a data link
layer protocol has not been specified.
10
Router Configuration

• Before you start configuring a Cisco router, you
  must understand the two EXEC modes that are
  available on a router.
• User EXEC Modeallows you to perform basic
  troubleshooting tests, telnet to remote hosts,
  and list some router system information router
  is in this mode if the prompt is the router name
  followed by the greater than sign. RouterBgt is
  an example of the user mode prompt.
• Privileged EXEC modesometimes called enable
  mode allows full router configuration and
  advanced troubleshooting RouterB is an example
  of the privileged mode prompt.
• User mode only requires that you log into the
  router via a console, telnet, or auxiliary port
  connection.
• Privileged mode requires that you issue the
  enable command.

11
Privileged Mode
12
Global Configuration Mode

• In order to configure Cisco routers, you must
  first enter Global Configuration Mode.
• Global configuration mode is used to configure
  router settings that affect overall router
  operation.
• To enter global configuration mode, you use the
  configure command from Privileged EXEC mode.
• The config t command is a faster way to enter
  global configuration mode. The t stands for
  terminal and is the default.
• The format of the global configuration mode
  prompt is router(config).

13
Interface Configuration Mode

• If you wish to configure a particular interface,
  you must use interface configuration mode. To
  enter this mode you must first be in global
  configuration mode.
• Once you are in global configuration mode, enter
  the interface command followed by the name and
  number of the interface you wish to configure.
• The command int e0 will allow you to configure
  the Ethernet 0 interface on the router.
• The format of the interface configuration mode
  prompt is routername(config-if).

14
Passwords

• Ciscos IOS provides a myriad of passwords for
  use on routers.
• The password types include console, virtual
  terminal line (VTY), auxiliary, enable, and
  enable secret passwords.
• You can accomplish the greatest security by using
  several passwords in conjunction with each other.
• You should always use a console password,
  otherwise once someone gets physical access to
  the router, they can get into it.
• In order to configure the console password, you
  must enter line configuration mode.

15
Console Password Configuration

• Issuing the commands shown below requires that
  all users trying to access the router via the
  console port, know the console password.

16
Prompting for the Console Password
17
VTY Password Configuration

• Passwords can be configured on virtual terminal
  lines.
• VTY passwords protect against unauthorized people
  telnetting into the router.
• Five VTY lines exist on every router by default.
• To configure the VTY passwords you must enter
  line configuration mode and add the login and
  password commands.
• This configuration is like the configuration for
  the console port password. A password can also be
  configured on the auxiliary port which will limit
  access via a modem.

18
VTY Password Configuration

• Issuing the commands shown below requires that
  all users trying to access the router via telnet
  know the vty password.

19
Enable and Enable Secret Passwords

• Once the router is entered, the single most
  important password, the enable mode password, can
  stop them from actually reconfiguring the router.
• There are actually two enable passwords. The
  enable password password command creates an
  enable mode password that is stored in the
  startup-configuration file in plain text.
• It is preferable to configure the enable secret
  password with the enable secret password
  command.
• The enable secret password overrides the enable
  password and is stored in encrypted form in the
  configuration files.

20
Enable and Enable Secret Passwords

• Output from the show run command displays the
  enable password in plain text and the enable
  secret password in encrypted form.

The enable secret password is stored in an
encrypted form for increased security.
The enable password is stored as plain text and
can pose a security risk.
21
The Ping Command

• The Ping command is used to verify if
  connectivity exists between hosts.
• When you issue the ping command followed by an IP
  address, the source computer sends out ICMP Echo
  request packets to the specified destination
  computer.
• The destination computer, if it is configured
  correctly, replies with ICMP Echo reply packets.
• A reply of five exclamation points means that all
  five Echo request packets were responded to with
  Echo reply packets. This is a successful ping.
• Standard ping can be entered from user EXEC mode
  or Privileged EXEC mode

22
Ping Command Output
23
Ping Responses
24
Extended Mode Ping Command

• Extended mode ping requires the user to be in
  Privileged EXEC mode.
• If you enter the ping command with nothing after
  it, you will be using extended mode ping.
• You will be prompted for the protocol, target
  address, repeat count (the number of request
  packets), datagram size, timeout, and other
  commands.
• The extended ping allows you to specify more Echo
  request packets and larger packets.
• Use this command to ping IPX nodes with the IPX
  protocol.

25
Extended Mode Ping Output
26
The Trace Command

• Another useful troubleshooting command is the
  trace command. The trace command is available
  from both user EXEC mode and Privileged EXEC
  mode.
• Trace shows the exact path a packet takes from
  the source to the destination. This is
  accomplished through the use of the time-to-live
  counter.
• The packet is sent out first with a TTL of one.
  Once it finds the first hop on the path to the
  destination, the packet is returned with a
  destination unreachable message. The TTL is
  incremented to two and the packet is resent.
• This process continues until the packet reaches
  the destination or times out.

27
Trace Command Output
28
The Debug Command

• The most powerful troubleshooting tool to master
  is the debug command. This command is only
  available from Privileged EXEC mode.
• Debug has numerous subcommands that allow you to
  troubleshoot particular protocols. It also has a
  debug all mode which will display all debugging
  counters at the cost of severe network
  performance degradation.
• The debug ip rip command can be used to
  troubleshoot RIP issues. The debug ip igrp
  transactions command is used to display
  statistics on igrp.
• Turn debugging off as soon as you are through
  troubleshooting. The no debug all command will
  turn off all debugging.

29
Debug IP Rip Output
30
Chapter Summary

• Router components include RAM, NVRAM, ROM, Flash,
  and the Interfaces.
• The two most important router configuration modes
  are Global Configuration Mode and Interface
  Configuration Mode.
• Global Configuration Mode manages parameters that
  affect overall router operation.
• Interface Configuration Mode allows you to
  configure individual interface parameters.

31
Chapter Summary Continued

• Ping, trace, and debug are all common
  troubleshooting commands on Cisco routers.
• The ping command checks for the status of a
  remote ip host. The extended mode ping command
  allows other protocols and parameters.
• The trace command allows an administrator to
  follow the path a packet takes from source to
  destination.
• For more advanced router troubleshooting, use the
  debug command to display router status updates.