Module 1 / Unit 2 Ethernet Flashcards
On completion of this unit, you will be able to: □ Understand the properties of transmission media, data signaling, and media access control. □ Describe the features of IEEE 802.3 (Ethernet). □ Describe the properties of MAC addressing and ARP. □ Understand the use of packet sniffers / protocol analyzers to capture and examine network traffic.
What is attenuation?
The loss of signal strength that occurs as the signal travels through the media
Why might the baud rate be different from the bit rate?
Baud is the number of symbols measured in Hertz; bit rate is the amount of information, measured in bits per second. A signaling technique might encode more than one bit per symbol.
With CSMA/CD, what will happen if a computer has data to transmit and there is already data on the cable?
The computer will wait until the cable is clear to transmit the data.
What is an MTU?
Maximum Transmission Unit - the amount of data that a frame payload can carry.
True or false? The CRC mechanism in Ethernet allows for the retransmission of damaged frames.
False. The CRC only indicates that a frame may be corrupt.
True or false? A computer with a 10BASE-T Ethernet adapter cannot be joined to a 100BASE-T network.
False - Fast Ethernet is backwards-compatible with 10BASE-T (and Gigabit Ethernet is backwards-compatible with Fast Ethernet).
You want to use fiber optic cabling to support 1 Gigabit Ethernet in a LAN. Which Ethernet standard should you use?
1000BASE-SX.
What is an I/G bit?
Determines whether a frame is addressed to a single node (0) or group (1). The latter is used for multicast and broadcast
If a mapping for a local destination host is not found in a source host ARP cache, how does the source host send an ARP request?
As a broadcast to all local hosts.
If a packet is addressed to a remote network, what destination MAC address will the sending node use?
The MAC address of the default gateway.
True or false? The arp utility allows you to discover another host’s MAC address.
Partially false - while that is the function of the Address Resolution Protocol, the arp utility is used to inspect the arp cache table, which may or may not contain the other host’s address. A standard means to ensure the MAC address is cached is to ping the destination address first (the basis of the arping utility).
On a switched network, what configuration changes must be made to allow a host to sniff unicast traffic from all hosts connected to a switch?
The network adapter must be put in p-mode (promiscuous mode) and the switch must be configured to mirror traffic to the sniffer’s port.
Write the command to use tcpdump to capture traffic from the IP address 172.16.16.254 on the interface eth0 and output the results to the file router.pcap:
tcpdump -I eth0 -w ‘router.pcap’ src host 172.16.16.254
