Question 1.
When troubleshooting an Ethernet network using Cisco IOS diagnostic commands, which of the following statistics would concern you?

a) MTU 1500 bytes
b) BW 10000 Kbit
c) DLY 1000 usec
d) rely 25/255
e) load 25/255

Answer

Question 2.
Why do collisions occur when one side of a point-to-point Ethernet link is configured for half-duplex and the other side is configured for full-duplex?

a) A full-duplex station cannot complete the carrier sense operation correctly if its partner is configured for half-duplex.
b) A half-duplex station cannot complete the carrier sense operation correctly if its partner is configured for full-duplex.
c) A half-duplex station reports a collision when it receives data while sending data. A full-duplex station sends data even when it is receiving data.
d) A full-duplex station reports a collision when it receives data while sending data. A half-duplex station sends data even when it is receiving data.

Answer

Question 3.
What process resulted in the following protocol analyzer output?

Ethernet Header
Destination:  FF:FF:FF:FF:FF:FF  Ethernet Broadcast
Source:       00:00:0C:05:3E:80
Protocol Type:0x0806
Protocol
Hardware:                 1  Ethernet (10Mb)
Protocol:                 0x0800  IP
Hardware Address Length:  6
Protocol Address Length:  4
Operation:                1 Request
Sender Hardware Address:  00:00:0C:05:3E:80
Sender Internet Address:  172.16.10.1
Target Hardware Address:  00:00:00:00:00:00
Target Internet Address:  172.16.10.10
Extra bytes (Padding):
................  00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
..                00 00
Frame Check Sequence:  0x00000000

Answer

Answers

Question 1.
When troubleshooting an Ethernet network using Cisco IOS diagnostic commands, which of the following statistics would concern you?

a) MTU 1500 bytes
b) BW 10000 Kbit
c) DLY 1000 usec
d) rely 25/255
e) load 25/255

Answer
d) rely 25/255

Explanation
Cisco IOS software displays the reliability of an Ethernet segment as "rely," expressed as a fraction of 255. 25/255 is less than 10% reliability and probably indicates a problem. The "rely" statistic documents the fraction of frames that arrived without input errors. It also takes into account the number of collisions encountered while sending. A low reliability on an Ethernet network segment with low load and few collisions is usually the result of a hardware problem such as a bad cable, bad connection, or external electrical noise.
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Question 2.
Why do collisions occur when one side of a point-to-point Ethernet link is configured for half-duplex and the other side is configured for full-duplex?

a) A full-duplex station cannot complete the carrier sense operation correctly if its partner is configured for half-duplex.
b) A half-duplex station cannot complete the carrier sense operation correctly if its partner is configured for full-duplex.
c) A half-duplex station reports a collision when it receives data while sending data. A full-duplex station sends data even when it is receiving data.
d) A full-duplex station reports a collision when it receives data while sending data. A half-duplex station sends data even when it is receiving data.

Answer
c) A half-duplex station reports a collision when it receives data while sending data. A full-duplex station sends data even when it is receiving data.

Explanation
A station configured for full-duplex operations has no need to sense carrier before sending, so it doesn't. Sending while receiving is normal and is not a collision.

A half-duplex station, however, does normal CSMA/CD. It listens before it sends and listens while it sends. If a half-duplex station receives data while it is sending, it assumes that the data is the result of a collision.
[4056]

Question 3.
What process resulted in the following protocol analyzer output?

Ethernet Header
Destination:  FF:FF:FF:FF:FF:FF  Ethernet Broadcast
Source:       00:00:0C:05:3E:80
Protocol Type:0x0806
Protocol
Hardware:                 1  Ethernet (10Mb)
Protocol:                 0x0800  IP
Hardware Address Length:  6
Protocol Address Length:  4
Operation:                1 Request
Sender Hardware Address:  00:00:0C:05:3E:80
Sender Internet Address:  172.16.10.1
Target Hardware Address:  00:00:00:00:00:00
Target Internet Address:  172.16.10.10
Extra bytes (Padding):
................  00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
..                00 00
Frame Check Sequence:  0x00000000

Answer
c) Station 172.16.10.1 is trying to find the Ethernet address for station 172.16.10.10.

Explanation
The protocol analyzer output shows an ARP frame sent by station 00:00:0C:05:3E:80 (172.16.10.1) to find the Ethernet address of 172.16.10.10. The protocol analyzer displays the Frame Check Sequence (FCS) as all zeros because the analyzer did not capture the contents of the FCS field. Many analyzers do not capture the contents of the FCS, although they do report the number of frames with bad FCSs.
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