CCNA2 Chapter 4

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CCNA2 Chapter 4
Learning about other Devices
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Cisco Discovery Protocol (CDP)

• Neighbor Discovery with CDP
• Scenario Assume your boss asks you to create a
  topology map of the network, including model
  numbers, IOS versions of Cisco equipment, etc.
  Now, suppose you are not in the building where
  the equipment is. You could use the Cisco
  Discovery Protocol (CDP) to gather information of
  directly connected Cisco neighbors.
• CDP is
• Cisco proprietary (as the name indicates)
• Operates at the Data Link layer
• Functions regardless of what Physical layer media
  yu are using (fiber, UTP, etc)
• Network layer routed protocol independent (IP,
  IPX, AppleTallk, etc)
• Enabled on all Cisco devices by default
• Sent as a multicast every 60 seconds out of all
  functioning interfaces, which enables neighbor
  Cisco devices collect information about each
  other.

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Cisco Discovery Protocol (CDP)

• CDP is used to
• gather hardware and protocol information about
  neighboring devices
• types of devices (switch, type of router)
• router interfaces they are connected to
• interfaces used to make the connection ( E0, S0,
  etc.)
• model number of the devices
• Best way to learn CDP is to do the labs!

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Cisco Discovery Protocol (CDP)
When a Cisco device boots up, CDP starts up
automatically and allows the device to detect
neighboring devices that are also running
CDP. CDP runs over the data link layer and
allows the two systems to learn about each
other. Each device configured for CDP sends
periodic messages, known as advertisements, to
multiple Cisco routers
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Cisco Discovery Protocol (CDP)
Primary use of CDP is to discover all Cisco
devices that are directly connected to a local
device. This is done by transmitting type length
values (TLVs) which are blocks of information
embedded in CDP advertisements.
To display the CDP information, use the command
show cdp
Shows information that can be configured in
Cisco devices CDP timer - how often CDP packets
are transmitted to all active interfaces CDP
hold time the amount of time that the device
will hold packets received from neighbor devices
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Cisco Discovery Protocol (CDP)
Merida show cdp Global CDP information
Sending CDP packets every 60 seconds Sending
a holdtime value of 180 seconds Sending CDPv2
advertisements is enabled Merida show cdp
neig Capability Codes R - Router, T - Trans
Bridge, B - Source Route Bridge S - Switch,
H - Host, I - IGMP, r - Repeater, P -
Phone Device ID Local Intrfce Holdtme
Capability Platform Port ID Internet Fas
0/0 168 R C2600
Fas 0/0 Vargas Ser 0/0 168
R C2600 Ser 0/0
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Cisco Discovery Protocol (CDP)

• Device TLVs displayed by the show cdp neighbors
  include
• Device ID (hostname of device directly
  connected)
• Local Interface (port or interface in which you
  received CDP packets)
• Holdtime (keeps track of how long it has been
  since you received information from that neighbor
  and how many seconds to wait until you consider
  that neighbor dead)
• Capability (router, switch, or repeater)
• Platform (the model number such as Cisco router
  2600, etc.)
• Port ID (interface in which the neighbor device
  sent out the CDP information)
• Supported by Cisco IOS release 12.0(3)T or later

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Cisco Discovery Protocol (CDP)
Sarasota show cdp neighbors Capability Codes R
- Router, T - Trans Bridge, B - Source Route
Bridge S - Switch, H - Host, I
- IGMP, r - Repeater, P - Phone Device ID
Local Intrfce Holdtme Capability Platform
Port ID Bradenton Ser 0/0 147
R PT1000 Ser 9/0 Miami
Ser 1/0 148 R PT1000
Ser 9/0 Sarasota
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Cisco Discovery Protocol (CDP)
To enable CDP globally
cdp run CDP is globally enabled by
default. NOTE on some switches (1900) cdp is not
enabled
To enable CDP on a particular interface, do
cdp enable On Cisco IOS Release 10.2 or higher,
CDP is enabled by default
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CDP Exercise
Create the topology in the graph
Change the hostnames to Bradenton, Sarasota and
Miami.
Assign IP addresses with their respective
masks Bradenton Serial 9/0 211.211.211.1
255.255.255.0 clock rate 56000 Sarasota
Serial 0/0 211.211.211.2 255.255.255.0 Sarasot
a Serial 1/0 200.200.200.1 255.255.255.0
clock rate 56000 Miami Serial 9/0
200.200.200.2 255.255.255.0
NOTE You may have different numbers for your
serial interfaces
From the Sarasota router, issue a show CDP
neighbors command. Your output should look like
the one from slide 8
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Cisco Discovery Protocol (CDP)

• NOTE
• Disable CDP at the global level with no cdp run
• If CDP is disabled globally, individual
  interfaces cannot be enabled for CDP
• IOS Release 10.3 or higher, CDP is enabled by
  default.
• To disable CDP on a specific interface after it
  has been enabled no cdp enable

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CDP Exercise 2 (Dissable CDP in local interface)
Test this with the Sarasota router. (You must be
in that interface first.) Sarasota(config)int
s1/0 Sarasota(config-if)no cdp enable Issue the
following command, and youll see info coming
form interface..? Sarasotashow cdp neig Now,
put it back the way it was Sarasota(config)int
s1/0 Sarasota(config-if) cdp enable
Sarasotashow cdp neig Sarasotashow cdp neig
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CDP Exercise 3 (Dissable CDP globally)
Test this with the Sarasota router.
Sarasota(config)no cdp run Issue the
following command, and youll see info coming
form interface..? Sarasotashow cdp neig Now,
put it back the way it was Sarasota(config) cdp
run and check it again Sarasotashow cdp
neig
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Clear cdp counters
Useful for resetting interface statistics on a
Cisco router
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Show cdp
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Show cdp entry
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Show cdp interface
Status of the carrier detect signal
Keepalive messages
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Show cdp neighbors
Know this output!
Routershow cdp neighbors detail will also give
the IP address of the neighboring Cisco device
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Telnet
Telnet is a virtual terminal protocol that is
part of the TCP/IP protocol suite. Provides a
remote login capability. Telnet function is at
the application layer. If a telnet command is
successful from one device to another, then all 7
layers of the OSI model is working. Cisco says
- It is the most complete testing mechanism
available. Telnet uses the five (5) vty
sessions. There has to be a login and
password associated with the vty session in
order for telnet to work. If a Telnet session is
left open for 10 minutes without activity, it
will automatically close itself.
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Reopening a suspended Telnet session

• Multiple Telnet sessions can be used and
  suspended by using the Ctrl-Shift-6, then x
  sequence.
• The session can be resumed by pressing Enter.
• Pressing the Enter key causes Cisco IOS to resume
  the most recently suspended session.
• The resume command can be used to start up a
  previous session, but must know the connection
  ID.
• Use the show sessions command to get the
  connection ID, then resume the correct session.

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Reopening a suspended Telnet session
It works with Packet Tracer!
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Telnet
If there is a host table on the router ( ip
host ltnamegt ltip addgt ), then you can do telnet
lthost namegt. As an example telnet routerB

• DO THE LABS FOR resuming and suspending SESSION.
• NOTE
• Pressing Enter takes you to the most recent
  session
• To resume a session it needs a connection ID.

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Ping
Ping command is used to determine if a particular
ip address is reachable. Traceroute command is
used to trace the route to an ip address. Ping
sends ICMP echo request messages and receive an
echo reply.
Ping Command Code Explanation ! ICMP echo reply
received . Nothing received U ICMP unreachable
(destination) received N ICMP unreachable
(network) received P ICMP unreachable (port)
received
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Interface Protocol
Serial is up, line protocol is up
operational
Serial is up, line protocol is down
Connection problems (L2)
Serial is down, line protocol is down
Interface problems (L1)
Serial is administratively down, line protocol
is down
Manually disabled
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Interface Protocol
For serial port Serial is up, line protocol is
down maybe caused by

• network mismatched

• clock rate not set on DCE

• mismatch of encapsulation (HDLC vs. PPP)

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Key terms
Hostname hostname Ip host hostname IP Ip
domain-lookup no ip domain-lookup Exec-timeout
minutes seconds show cdp neighbors show cdp
neighbors detail cdp run cdp enable telnet
IP_address