Section 5 Flashcards
Troubleshooting IPv4 Network Connectivity
1
Q
What should you check when there is no end to end connectivity between devices?
A
- Physical connections (cables, etc…)
- Route path (traceroute, route tables)
- Default gateways
- Name resolution
- Access Control Lists
2
Q
What does ACL stand for?
A
Access Control List
3
Q
What is an ACL?
A
A list kept by router to control access to or from the router for a number of services.
4
Q
What does ICMP stand for?
A
Internet Control Messaging Protocol
5
Q
What OSI layer does ICMP operate at?
A
Layer 3 (Network)
6
Q
What is ICMP used for?
A
To report errors and provide information that is relevant to IP pack processing.
7
Q
What RFC documents ICMP?
A
RFC 792
8
Q
What does SLA stand for?
A
Service Level Agreement
9
Q
What are three functions of the IP SLA measurements?
A
- Edge-to-edge network availability monitoring
- Network performance monitoring
- Troubleshooting network operation
10
Q
What command creates an IP SLA operation and enters the IP SLA configuration mode?
A
ip sla [operation #]
11
Q
What command configures an ICMP echo test for a specified destination?
A
icmp-echo [destination ip address]
12
Q
What is the command for scheduling when an IP SLA measurement will be taken?
A
ip sla schedule [parmeters]
13
Q
What are the parameters that can be used when you use the ip sla schedule command?
A
- life
- start-time
- ageout
- recurring
14
Q
What does the life keyword set in an IP SLA measurement?
A
How long the IP SLA test will run.
15
Q
How long will the IP SLA test run if you use the following command?
ip sla schedule life forever
A
Until you manually remove it.
16
Q
What keyword determines when the IP SLA test should start?
A
start-time
17
Q
What start-time keyword allows you start the IP SLA measurement immediately?
A
now
18
Q
What keyword controls how long IP SLA date is kept?
A
ageout
19
Q
What keyword lets you schedule an IP SLA test periodically?
A
recurring
20
Q
Can you modify an IP SLA test after it has been scheduled?
A
No
21
Q
What command lets you verify IP SLA configuration on a device?
A
show ip sla configuration
22
Q
What command lets you verify IP SLA statistics on a device?
A
show ip sla statistics
23
Q
What two tools should be used to test end to end connectivity?
A
ping and treaceroute
24
Q
What are the three main categories of issues that cause a failure of the network?
A
- hardware failures
- software failures (bugs)
- configuration errors
25
What can you do to check the status of an interface?
1. Check LEDs on the device
| 2. Use the show interfaces command in the CLI
26
What three steps can you try when you have a down interface?
1. Check that you have the correct cable type
2. Try replacing the suspect cable with a known good one
3. Enable the interface in the CLI
27
What output should you look to from the show interfaces command to identify interface/cabling issues?
1. Input queue drops
2. Output queue drops
3. Input errors
4. Output errors
28
What do Input Queue Drops indicate?
More traffic was delivered than could be processed. Usually indicates high CPU usuage.
29
What does LED stand for?
Light Emitting Diode
30
What do Output Queue Drops indicate?
That packets were dropped on the interface. Typically occurs when aggregate input traffic is higher than output capability. A network bottleneck is occurring.
31
What do Input errors indicate?
Errors were detected during the reception of the frame. Typically CRC errors.
32
What do CRC errors indicate?
cabling issues, duplex mismatches, and interface hardware problems.
33
What do Output errors indicate?
Output errors typically indicate data collisions over the wire. Usually the result of duplex mismatches.
34
What is the most common cause of interface errors?
Duplex mismatches
35
Point-to-point links should always be run at what duplex?
Full
36
When is autonegotiation for speed and duplex recommended?
For ports that are connected to non-critical endpoints.
37
When is manually setting the speed and duplex recommended?
On links between network devices and ports connected to critical endpoints.
38
What command is used to verify speed and duplex settings on an interface?
show interfaces [interface]
39
What standard defines physical layer and data link layer media access control of wired 1000BASE-T?
802.3ab
40
What does the 802.3ab standard define?
Physical and data link layer media access control of wired 1000BASE-T
41
What does NIC stand for?
Network Interface Card
42
What is a NIC?
A board that provides network communication capabilities to and from a computer system.
43
What does SMTP stand for?
Simple Mail Transfer Protocol
44
What is SMTP?
An Internet protocol used for providing e-mail services.
45
What command is used to view the routing table?
show ip route
46
What do the following routing codes in the routing table indicate:
L, C, S, R, O, D
```
L = Local host route
C = Directly connected route
S = Static Route
R = RIP
O = OSPF
D = EIGRP
```
47
Why does EIGRP use D for the routing code?
D is the first letter in the DUAL algorithm used by EIGRP
48
What types of routes are shown in the routing table?
1. Directly connected
2. Local host routes
3. Static routes
4. Dynamic routes
5. Default routes
49
What happens to a packet if there is no matching routing entry, and no default route is set?
The packet is dropped
50
What happens to a packet if there is no matching routing entry, and a default route is set?
The packet is sent towards the default route
51
What happens to a packet that matches a route entry?
The packet is sent to the interface defined in the route
52
What happens when packets match multiple entries with the same prefix (subnet mask)
The packets will be load balanced across the routes
53
What happens when packets match multiple routing entries with different prefixes?
The route with the most specific (higher) prefix is used
54
What does SPAN stand for?
Switch Port Analyzer
55
What is SPAN used for?
To copy traffic received on one port or VLAN to another port for analysis.
56
What is used in conjunction with SPAN to capture and analyze traffic?
A packet sniffer (e.g. Wireshark)
57
What are two rules to keep in mind when configuring SPAN?
1. A destination port cannot be a source port, or vice versa.
2. The destination port is no longer a normal switchport - only monitored traffic passes through.
58
What is SPAN identified by?
A session number
59
What command is used to associate SPAN with a source port?
monitor session [number] source interface [interface]
60
What command is used to associate SPAN with a destination port?
monitor session [number] destination interface [interface]
61
What command is used to verify the default gateway on a route?
show ip route
62
What commands can be used to verify a default gateway on a Windows device?
1. route print
| 2. ipconfig /all
63
What does FTP stand for?
File Transfer Protocol
64
What is FTP use for?
Exchanging files over the Internet
65
How can the mapping of computer names to IP addresses be accomplished?
1. Statically via a hosts file
| 2. Dynamically via DNS
66
What can you use in place of an IP when using ping or traceroute?
A hostname
67
What three locations can you modify IP to name mappings of a network?
1. The local host file on a PC
2. The DNS server
3. A Cisco switch or router
68
Where is the host file located on a Windows PC?
C:\Windows\System32\drivers\etc
69
What command is used to map a name to IP on a Cisco device?
ip host [name] [address]
70
What does a typical TCP/IP packet include?
1. Frame Header
2. IP Header (packet)
3. TCP Header (segment)
4. Data
71
What can extended ACLs test packets by?
1. Protocol (IP, TCP, UDP)
2. Source Address
3. Destination Address
4. Port Number
72
What are the two types of extended ACLs?
1. Named
| 2. Numbered
73
What number ranges indicate an extended ACL?
100 - 199, 2000 - 2699
74
What command is used to create an extended named ACL?
ip access-list extended [name]
75
What command and parameters are used in an ACL permit or deny statement?
[permit | deny] [protocol] [(source ip) (source wildcard) | any | (host) (source ip | hostname)] [(operator) (port)] [(destination ip) (destination wildcard) | any | (host) (destination ip | hostname)] [(operator) (port)
76
What are the most commonly specified protocols in an extended ACL?
IP, TCP, UDP, ICMP
77
What are the most common operators specified in an extended ACL?
lt (less than), gt (greater than), eq (equal), neq (not equal), and range (inclusive range)
78
What command applies an ACL to an interface in the inbound or outbound direction?
ip access-group [ACL name] [in | out]
79
What does TCP stand for?
Transmission Control Protocol
80
At what layer does TCP operate?
Layer 4 (Transport)
81
What is TCP?
Connection oriented transport layer protocol that provides reliable full duplex data transmission.
82
What does UDP stand for?
User Datagram Protocol
83
Is UDP connection oriented or connectionless?
Connectionless
84
What is the primary advantage of UDP over TCP?
Speed
85
What RFC defines UDP?
RFC 768
86
What command is used to view ACLs on the router?
show ip access lists
87
What command is used to determine where ACLs are applied?
show ip interface [interface]
88
What is a better syntax for the show ip interface command when wanting to identify ACLs on an interface?
show ip interface [interface] | include access list
89
What does DNS stand for?
Domain Name System
90
List six useful troubleshooting commands.
1. show ip route
2. sh ip interface brief
3. show run | section interface
4. show ip interface
5. ping
6. traceroute
91
In IOS what does the "." (dot) character indicate in an ICMP echo request
No reply
92
In IOS what does the "U" character indicate in an ICMP echo request?
Network unreachable
93
What happens when you use telnet to connect to a port on a device that is not open?
The connection will be refused.
