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NET4009 > Week 1: Troubleshooting approaches > Flashcards

Week 1: Troubleshooting approaches Flashcards

1
Q

What is the troubleshooting process?

A

1 - Defining the problem
2 - Gathering information
3 - Analyzing information
4 - Eliminating possible causes
5 - Formulating / proposing a hypothesis
6 - Testing hypothesis

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2
Q

Is the shoot-from-the-hip a good approach?

A

Quite ineffective for inexperienced troubleshooters and huge set backs when it does not yield immediate results.

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3
Q

What are all the troubleshooting approaches?

A
  • Top-down
  • Bottom-up
  • Divide-and-conquer
  • Follow-the-path
  • Spot-the-difference
  • Move-the-problem
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4
Q

What are the logging severity levels?

A

(0) Emergency
(1) Alert
(2) Critical
(3) Error
(4) Warning
(5) Notification
(6) Informational
(7) Debugging

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5
Q

What do these commands mean?
logging buffered 16384
logging console warnings
logging 10.1.152.1

A
  • logging buffered 16384
    Messages are logged to a circular buffer in RAM, that is limited to 16384 bytes
  • logging console warnings
    logging messages are limited to level 4 (warnings) and lower
    By default every logging message is enabled

logging 10.1.152.1
messages are logged to a syslog server at IP

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6
Q

What are the functions of the control plane?

A

Responsible for processing Layer 2 and Layer 3 control packets. (e.g. OSPF, ISIS, STP, CDP)

Responsible for procession packets that cannot be CEF switched

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7
Q

What are the protection mechanism of the control plane?

A
  • Control Plane Policing (CoPP)
  • Access lists to control routing updates
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8
Q

What are the key show commands for troubleshooting the control plane?

A
  • show processes cpu
  • show ip arp
  • show ip route
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9
Q

What are the functions of the management plane?

A

Responsible for management functions for a network device.

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10
Q

What are the protection mechanism for the management plane?

A
  • Management plane protection
  • Access lists to limit users access to Telnet
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11
Q

What are the key show commands for troubleshooting the management plane?

A
  • show snmp user
  • show snmp view
  • show ip ssh
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12
Q

What are the functions of the data plane?

A

Responsible for the switching / forwarding of data packets through the network device using specialized hardware

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13
Q

What are the protection mechanism of the data plane?

A

Access lists to block unwanted users or traffic

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14
Q

What are the key show commands for troubleshooting the data plane?

A
  • show ip cef
  • show adjacency table
  • show cef not-cef switched
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15
Q

What are CEF’s data structures?

A

Forwarding Information Base (FIB):
- reflects the routing table with all recursive lookups resolved
- a lookup up in the FIB results in a pointer to an adjacency entry in the adjacency table

CEF Adjacency Table
- consists of egress interface only for a point-to-point interface or an egress interface and next-hop IP address for a multipoint interface

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16
Q

Which commands do you use to verify CEF’s FIB and Adjacency table?

A
  • show ip cef “ip-address”
  • show ip cef “network-mask”
  • show adjacency detail
17
Q

How should you use the ip debug command?

A
  • Always use an access-list
    access-list 101 permit tcp any any eq telnet
    debug ip packet detail 101
18
Q

What do the numbers mean in “show processes cpu”?

A

CPU utilization for five seconds: 30% / 26% ; one minute: 31% ; five minutes: 14%

  • 30%, 31%, 14% : Total CPU spent on processes and interrupts
  • 26% CPU spent on interrupts
  • Total time spent on processes: 30% - 26%
19
Q

What are the DHCP messages?

A

Discover
Offer
Request
Acknowledge

20
Q

What is a DHCP relay agent?

A

DISCOVER messages are sent as broadcast, but cannot leave the router boundary. You can use a boundary router to send DISCOVER messages further into the network towards the actual server

21
Q

What are the commands for troubleshooting DHCP?

A

show ip dhcp conflict
show ip dhcp binding
debug ip dhcp server packet

22
Q

What is SLAAC?

A

StateLess Address Auto Configuration: preferred method of assigning IP addresses in an IPv6 network
The device sends the router a request for the network prefix, and then uses this prefix with its own MAC address to create an IP address.

23
Q

How do you troubleshoot SLAAC?

A
  • show ipv6 interface g0/0
    -> check if RAs are suppressed
  • only works if route is using a /64 prefix
  • check if IPv6 unicast routing is enabled
24
Q

What is stateful DHCPv6?

A

It provides an IP address to the device as well as other information such as NTP server, DNS, etc.

25
Q

What is stateless DHCPv6?

A

It provides the client with an IP address, a default gateway, and tells it to contact a DHCPv6 server for other information

NET4009 (3 decks)

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