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network administration > week 4 > Flashcards

week 4 Flashcards

1
Q

ethernet is defines by ________ and __________ protocols

A

physical layer and data link layer protcols

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2
Q

what are the 2 primary responsibilities of the mac

A

data encapsulation

media access control

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3
Q

the mac sublayer encapsulates the Network layer pdu with a header and trailer to create the ________ before sending it out

A

frame

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4
Q

the trailer contains a cyclic redundancy check of the frame contents for ________–

A

error detection

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5
Q

the mac sublayer directly communicates with the __________-

A

physical layer

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6
Q

If multiple devices on a single medium attempt to forward data simultaneously, the data will collide resulting in corrupted, unusable data. How does ethernet solve this problem

A

ethernet controls the problem using carrier sense multiple access (CSMA) where a device that wishes to transmit data will

  • -> check the media if it is carrying a signla
  • -> if no signal is detected, the device transmits the dat a
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7
Q

CSMA is usually implemented together with a method for resolving media contention. What are those methods .

A 
CSMA/CD = collision detection 
CSMA/CA = collision avoidance
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8
Q

what is CSMA/CD used for

A

wired ethernet

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9
Q

what happens in csma/cd

A
  • -> the device checks the media for presence of data signal
  • -> If there is no data signal, it shows that the media is free. The device can transmit data .
  • -> If signals are detected, it shows that another device is transmitting. The device will wait until the media is free
  • -> modern networks today uses intermediate network devices like switches that prevent collisions between end-devices such that csma/cd is no longer necessary
  • -> wireless connections in lan still have to take collisions into account
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10
Q

what are the steps in CSMA/CA

A
  • -> Wireless device examines the media for the presence of data signal
  • -> If the media is free, the wireless device sends a notification across the media of its intent to use it
  • -> The device then sends the data.
  • -> Used by 802.11 wireless networking technologies
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11
Q

how many hexadecimal bits is mac address

A

48-bit binary value expressed as 12 hexadecimal digits.

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12
Q

what rules must mac address follow

A

IEEE requires a vendor to follow these rules:

  • Must use that vendor’s assigned Organizationally Unique Identifier (OUI) as the first 3 bytes.
  • All MAC addresses with the same OUI must be assigned a unique value in the last 3 bytes.
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13
Q

what happens during the ethernet operation: frame processing

A

–> before a device can forward a frame to the ethernet network, it attaches header information to the packet which contains the source and destination mac addresses

–> When a device receives a frame, the NIC checks the frame header to see if the destination MAC address matches its physical MAC address stored in RAM

–> No match, the device discards the frame

–> If it matches, the NIC passes the frame up the OSI layers, where further de-encapsulation processes take place.

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14
Q

_____________ is the ethernet frame format used in TCP/IP networks

A

Ethernet II

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15
Q

what is the speed of ethernnet

A
  • -> early versions of ethernet were slow at 10Mb/s.

- -> Now operate at 10Gb/s and faster

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16
Q

mac address is also called ________-

A

physical address

17
Q

what are the fields inside ethernet frame

A

preamable, start frame delimiter - used for synchronization between sending and receiving devices

length/type - defines the length of the frame’s data field and list which protocol is implemented

data - contains the encapsulated data from a higher layer, an IPv4 packet

frame check sequence - used to detect for error using cyclic redundancy checks

18
Q

what is broadcast mac address

A

ff:ff:ff:ff:ff:ff

19
Q

differences between IP and MAC address

A
  • -> mac address does not change but IP address can change
  • -> mac address is called physical address as it is physically assigned to the host NIC whereas IP address is called logical address as it is assigned logically (assigned by network admin)
  • -> IP address is based on where the host is located
20
Q

what is the purpose of the address resolution protocol (ARP )

A
  • -> resolve the IPv4 to mac address mapppings to create the frame
  • -> maintain a table of these mappings
21
Q

what is an ARP table

A
  • -> A table in devices listing the physical MAC addresses of destination IP addresses
  • ->Mapping entries are created when a device receives a layer 2 frame
22
Q

what is ARP request

A
  • -> layer 2 broadcast to all devices on the ethernet LAN
  • -> The node that matches the IP address in the broadcast will reply
  • -> In no device responds to the ARP request, the packet is dropped because the frame cannot be created
23
Q

______________ entries can be entered in the ARP table, but this is rarely done

A

static map entries

24
Q

what happens if the destination host is in a different subnet

A
  • -> computer will use the mac address of the default gateway
  • -> If the computer does not know the mac address of the default gateway, an arp request is sent out to retrieve the mac address of the default gateway.
25
Q

what does a layer 2 lan switch do

A
  • -> connects end devices to the network
  • -> performs switching and filtering based only on mac addresses
  • -> Builds a mac address table which maps Mac addresses to port number s
  • -> uses the mac address table to make forwarding decisions
  • -> Requires routers to route data between different subnets
26
Q

what are the steps when the switch uses the mac address table

A
  • -> the switch receives a broadcast frame from the source host to port 1
  • -> The switch enters the source mac address and the switch port that received the frame into the address table
  • ->Because the destination address is broadcast, the switch floods the frame to all ports, except the port on which it received the frame
  • -> The destination device replies to the broadcast with a unicast frame addressed to the source host.
  • -> the switch enters the source and MAC address of the destination device and the port number of the switch port that received the frame into the address table. The destination address of the frame and its associated port is found in the MAC address table
  • -> the switch can now forward frames between source and destination devices without flooding because it has entries in the address table that identify the associated ports.
27
Q

what is half duplex (CSMA/CD)

A
  • -> unidirectional data flow
  • -> higher potential for collision
  • -> hub connectivity
28
Q

what is full duplex

A
  • -> point to point only
  • -> attached to dedicated switched port
  • -> Requires full duplex support on both ends
  • -> collision-free
  • -> collision detect circuit disabled

network administration (10 decks)

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