CCNA2 Module 9

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CCNA2 Module 9

• By Larry Twigg

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Show IP Route
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Show IP Route (cont.)

• Show IP Route will give routing table.
• Gives the networks directly connected.
• C is directly connected.
• Gateway of last resort is not set therefore only
  the directly connected networks will have packets
  forwarded.

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Gateway of last resort

• Default Route
• IP default-network 192.168.17.0
• Assigns destination path for anything not in
  routing table to 192.168.17.0 network.
• IP Route 0.0.0.0 0.0.0.0 192.168.1.2
• If the router does not have the network in
  routing table it will send the packet to
  172.16.1.2

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L2 and L3 Addresses

• Source MAC Address
• The device sending at that point
• Changes each step
• Destination MAC
• The next hop device at that point
• Changes each step

• Source IP
• IP of first sending device
• Does not change
• Destination IP
• IP of final destination
• Does not change

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Administrative Distances
The lower the number the more trustworthy the path

• Connected
• Static
• EIGRP (Internal)
• IGRP
• OSPF
• RIP

• 0
• 1
• 90
• 100
• 110
• 120

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Metrics

• RIPv1 hop count only
• Static Metrics Bandwidth and delay
• Dynamic Metrics Load and Reliability
• IGRP default uses static
• IGRP formula
• Metric K1Bandwidth (K2Bandwidth)/256-load)
  K3Delay
• Default K11, K31, K20

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RIP in Show IP route

• Known via Rip
• To get to 200.200.200.0/24 go through
  192.168.10.2
• Administrative distance is 120
• Route metric is 1 meaning it is on the next
  router.

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Show IP Protocols

• Updates 30sec
• Invalid 6 x 180
• Discarded 8 x 240
• Networks
• 192.168.0.0
• 192.168.10.0
• Gateway 192.168.10.2

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Show IP RIP Database
Last update was 20 second ago.
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Load Balancing

• Two paths FastEthernet0/0 and Serial 0/0
• Two metrics 8486 and 10476
• Can be verified by ping

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Show IP Route with IGRP

• I IGRP
• 192.168.30.0/24 through 192.168.10.2
• Administrative Distance 100
• Metric 10976
• Last Update 35 seconds
• Interface Serial 0/0

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Trouble shooting

• Application Telnet
• Presentation
• Session
• Transport
• Network Ping, IP addressing
• Data Link MAC Address, No Clock Rate
• Physical Wire, connections, Show controller,
  Show interface.

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Five Step Trouble Shooting

• Collect all available information and analyze the
  symptoms of failure
• Localize the problem to within a single network
  segment, to a single complete module or unit, or
  to a single user
• Isolate the trouble to specific hardware or
  software within the unit, module, or users
  network account.
• Locate and correct the specific problem.
• Verify that the problem has been solved.

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OSI Trouble Shooting Method

• Go through each layer and do checks.
• Start at the Physical layer and go to the
  Application layer until problem is solved.

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Layer 1 Errors

• Broken cables
• Disconnected cables
• Cables connected to the wrong ports
• Intermittent cable connection
• Wrong cables used for the task at hand
  Transceiver problems
• DCE cable problems
• DTE cable problems
• Devices turned off

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Layer 1 Things to check

• Link lights interface card may be installed
  wrong. Reseat it.
• Link Lights Faulty cable
• Cables connected to the correct ports
• Switch and hub ports in the correct VLAN or
  collision domain.
• Verify proper cables Crossover or straight
  through
• Correct transceiver type, properly connected,
  properly configured.

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Layer 2 Errors

• Improperly configured serial interfaces
• Improperly configured Ethernet interfaces
• Improper encapsulation set (HDLC is default for
  serial interfaces)
• Improper clockrate settings on serial interfaces
• Network interface card (NIC) problems

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Layer 3 Errors

• Routing protocol not enabled
• Wrong routing protocol enabled
• Incorrect IP addresses
• Incorrect subnet masks

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Layer 3 Ping

• The ping utility is used to test network
  connectivity
• Ping uses ICMP to verify the hardware connection
  and the logical address of the network layer
• ! indicate each successful echo
• . indicate the application on the router timed
  out
• Use of an extended ping.

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Telnet Utility and problems

• The telnet utility is a virtual terminal protocol
  that is part of the TCP/IP suite.
• Telnet proves that at least one application can
  go through all 7 layers.
• Telnet to one router and not another
  addressing, naming, or access permission
  problems.

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Telnet problems (cont)

• Can a reverse DNS lookup on the client's address
  be found? Many Telnet servers will not allow
  connections from IP addresses that have no DNS
  entry. This is a common problem for DHCP-assigned
  addresses in which the administrator has not
  added DNS entries for the DHCP pools.

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Telnet Problems (cont)

• It is possible that a Telnet application cannot
  negotiate the appropriate options and therefore
  will not connect. On a Cisco router, this
  negotiation process can be viewed using debug
  telnet.
• It is possible that Telnet is disabled or has
  been moved to a port other than 23 on the
  destination server.

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Show interface serial 0/0

• Operational
• Serial 0/0 is up, line protocol is up
• Connection Problem
• Serial 0/0 is up, line protocol is down
• Interface Problem
• Serial 0/0 is down, line protocol is down
• Disabled
• Serial 0/0 is administratively down, line
  protocol is down

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Show interfaces serial 0/0

• Increase Carrier transitions
• Line interruptions due to problems in the service
  provider network.
• Faulty switch, DSU, or router hardware.
• Input errors
• Faulty telephone company equipment
• Noisy serial line
• Incorrect cable or cable length
• Damaged cable or connection
• Defective CSU or DSU
• Defective router hardware
• Interface Resets
• Too many missed keepalives
• Bad line causing carrier transitions
• Possible hardware problem at the CSU, DSU, or
  switch

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Counters 0
If the show interfaces output shows the last
clearing of the counters as never, use the show
version command to find out how long the router
has been functional.
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Show Version for Time Check
Use the clear counters command to reset the
counters to zero. These counters should always be
cleared after an interface problem has been
corrected. Starting from zero gives a better
picture of the current status of the network and
will help verify that the issue has indeed been
corrected. Do Lab Activity 9.3.1
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Show interface Up and down

• Line Physical Layer
• If line is down, protocol is always down
• Protocol Data Link Layer
• No keepalives - If the interface misses three
  consecutive keepalives, the line protocol is
  marked as down.
• No clock rate
• Mismatch in encapsulation type
• The show interfaces serial command should be used
  after configuring a serial interface to verify
  the changes and that the interface is operational.

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Show Cdp Neighbors

• The output from the show cdp neighbors command
  displays information about directly connected
  neighbors.
• This information is useful for debugging
  connectivity issues.

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Show CDP Neighbors Details
If you think a cabling problem exists do a no
shutdown on interfaces and a show cdp neighbors
details.
One area of concern with CDP is security. The
amount of information CDP provides is so
extensive that it can be a potential security
hole. For security reasons CDP should be
configured only on links between Cisco devices
and disabled on user ports or links that are not
locally managed.
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Traceroute

• The traceroute command is used to discover the
  routes that packets take when traveling to their
  destination.
• The output can be captured and used for future
  troubleshooting of the internetwork.
• Traceroute output will also indicate the specific
  hop at which the failure is occurring.
• If an asterisk () appears, the packet failed.
• UDP are sent with increasing TTL counts. Router
  responds with an ICMP TEM (time exceeded message.

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Show IP Route Output
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Show IP Route

• The output from the show ip route command shows
  the entries for all known networks and
  subnetworks, and how that information was
  learned.
• If there is a problem reaching a host in a
  particular network, then the output of the show
  ip route command can be used to verify that the
  router has a route to that network.
• If the output of the show ip route command does
  not show the expected learned routes or no
  learned routes, then the problem is possibly that
  routing information is not being exchanged.

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Show IP Protocols

• Shows values about IP routing protocol
  information on the entire router.
• Protocols configured
• Networks being advertised
• Which interfaces are sending updates
• Sources of routing updates
• Also shows
• Timers
• Filters
• Route summarization
• Route redistribution
• Taking a baseline will help later diagnostics

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Show Controllers Serial

• Used to determine the type of cable that is
  connected
• Can also determine no cable, wrong cable, or
  defective cable
• Queries the integrated circuit (chip) that
  controls the serial interfaces and displays
  information about the physical interface.

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debug

• The debug command is used to display dynamic data
  and events.
• The dynamic output of the debug command comes at
  a performance cost, producing high processor
  overhead that may disrupt normal router
  operation.
• debug should be used isolate problems and not to
  monitor normal network operation.
• Debug should not be used with a Telnet session,
  If absolutely necessary use terminal monitor to
  direct output.

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Other Debug commands

• Timestamps puts a timestamp on a debug message.
  Gives duration between events.
• No debug all undebug all turns off all
  diagnostic output.
• Debug ip rip monitoring RIP
• Show debugging what is currently being examined
  by a debug command.