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IT 377 - Practical Telecommunication Networking > Test 2 Study Guide > Flashcards

Test 2 Study Guide Flashcards

1
Q

What IEEE standard added full duplex flow control?

A

Full duplex flow control was added as a part of IEEE 802.3X.

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2
Q

What is full duplex flow control?

A

Full duplex flow control is a reference to IEEE 802.3X, wherein a station operating in full-duplex can send a PAUSE frame to the multicast address, wherein the sender will know to delay further transmission by the amount of time specified in the frame.

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3
Q

What IEEE standard added the Spanning Tree Protocol?

A

The Spanning Tree Protocol was added in IEEE 802.1D.

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4
Q

What is the spanning tree protocol?

A

Spanning tree protocol is a network protocol that ensures the absence of any network loops within a network layout that would normally have them. It exchanges data between bridges to build a picture of what the whole network looks like.

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5
Q

How does the spanning tree protocol work?

A

The spanning tree protocol first sends out Bridge Protocol Data Units from each switch to determine the network topology. It then decides which bridge will become the “root bridge”, the bridge that will act as the controller for STP. This is by default the bridge with the lowest IP address.
The next step is to identify root ports. There will be only one root port per bridge, which is the one with the shortest path to the root bridge.
After the root ports are set, designated ports are set, as are blocked ports. A designated port is always at the other end of a root port, and on connections where there is no root port, one becomes designated (the one with the lower address), and the other becomes blocked.

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6
Q

What are Bridge Protocol Data Units?

A

Bridge protocol data units are packets that are sent out by bridges in an spanning tree protocol network periodically, that contain information about the network’s setup.

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7
Q

What is a root port? How is it identified?

A

A root port is a port that is on the shortest path back to the root bridge.

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8
Q

What is a root bridge? How is it identified?

A

A root bridge is a concept in the spanning tree protocol where the switch with the lowest MAC address becomes the “controlling” switch.

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9
Q

What is a designated port?

A

A designated port is a port in the listening state. All ports on the root bridge are designated ports. In the case where a port could be either designated or blocked, the port with the least cost will become designated; if they are tied, the one with the lowest ID will become designated.

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10
Q

What IEEE standard implemented Rapid STP?

A

IEE 802.1W implemented Rapid STP.

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11
Q

What is Rapid STP?

A

Rapid STP, or rapid spanning tree protocol, is a variant of the spanning tree protocol, but it provides a significant speed increase in recovery after a topology change.

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12
Q

What IEEE standard implemented link aggregation?

A

IEEE 802.3AD implemented link aggregation.

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13
Q

What is link aggregation?

A

Link aggregation is a method of combining multiple network connections in parallel in order to increase throughput. It was implemented in IEEE 802.3AD

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14
Q

In what IEEE standard implementation was Quality of Service implemented?

A

Quality of Service was implemented in IEEE 802.1P.

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15
Q

What is Quality of Service?

A

Quality of service is a method of determining the order by which traffic should be processed, based on its priority.

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16
Q

What are the three main standards of Quality of Service?

A

The three main standards of Quality of Service are Voice Service, Gold Service (data), and Best Effort (data). Best effort means the best effort will be given to process it, after everything else is done.

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17
Q

What is the operation mode of most modern Ethernet switches?

A

Most modern Ethernet switches operate in store-and-forward mode. This is because it allows for error checking, and with the speed of current switches, there’s no loss of service.

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18
Q

What are the states of STP? What happens in each?

A

The states of STP are:

  • Listening - Will only send/receive BPDU to participate.
  • Learning - Same as listening, but it will populate its MAC table to become a forwarding state later.
  • Forwarding - Forwards frames and sends/receives BPDU.
  • Blocking - Only receives BPDU
  • Disabled - Will not send or receive BPDUs or data.
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19
Q

What are the states in RSTP? How are they different from STP?

A

The states of RSTP are:

  • Discarding - No user data is sent over the port.
  • Learning - Still not forwarding frames, but populates MAC table
  • Forwarding - Normal operation.
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20
Q

What are the timers used in STP? What do they each do?

A

STP’s timers are:

  • Aging Timer: How long a MAC address is kept in a bridge’s forwarding database after having received a packet from that address. 300s default.
  • Forward Delay Timer: Time spent in Listening & Learning before entering Forwarding. 15s default.
  • Hello Timer: The interval at which BPDU packets are sent out by the root & designated bridges.
  • Max Age Timer: If the last received hello packet is older than this timer, a topology change has occurred.
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21
Q

What is the primary advantage of RSTP vs STP?

A

The prime advantage of RSTP is that its fail-over time is considerably shorter.

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22
Q

How does RSTP differ from STP in regards to BPDUs?

A

In RSTP, all bridges generate “Hello” BPDU packets to “keep alive” the current configuration.

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23
Q

How does Half Duplex Ethernet implement the flow control function?

A

Half duplex Ethernet implements flow control by using backpressure; that is, it sends a frame back down the line in order to cause a collision.

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24
Q

What is the MAC control frame defined in 802.3x?

A

The MAC control frame defined in 802.3x is PAUSE. The PAUSE frame is usable only in full duplex, and requests that the sender waits an amount of time specified in the frame before continuing to send.

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25
Q

How many VLANs can be defined by the 802.1Q standard?

A

The 802.1Q standard can define up to 4096 VLANs. This is because there is a 12-bit field within the tag control information for the MAC frame. 2^12 = 4096

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26
Q

. What is the max frame size of an 802.1Q tagged frame?

A

The maximum frame size of an 802.1Q tagged frame is 1522 bytes.

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27
Q

If the Hello Timer is 2 seconds, which is the general (e.g., non LOS) failure detection time in RSTP?

A

The general failure detection time in RSTP will be 6 seconds, if the Hello Timer is 2 seconds. This is because in RSTP, a failure is detected if a Hello isn’t received three times in a row. 2 x 3 = 6 seconds.

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28
Q

How do switches/bridges exchange control information with one another?

A

Switches/Bridges exchange control information through the use of Bridge Protocol Data Units, or BPDUs.

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29
Q

How many priority queues can be specified in an 802.1p-enabled frame?

A

There can be up to 8 priority queues in an 802.1p-enabled frame. This is because in an 802.1p-enabled frame, there is a three-bit field for user priority. 2^3 = 8 priority queues.

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30
Q

The VLAN ID is added to a 802.1Q-tagged frame by what?

A

The VLAN ID is added by the “ingress switch”, basically, the port that traffic passes through to join the VLAN.

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31
Q

How is expected throughput calculated?

A

Expected throughput is calculated out using the following equation:
(Frame Size - 18) / (8 + Frame Size + 12) * Bandwidth

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32
Q

How is fail-over time in STP estimated?

A

Fail-over time in STP is calculated by taking the Max Message timer and adding it to two times the Forward Delay.
Max Message + 2 * Forward Delay = Fail-Over Time

33
Q

How would you test link aggregation performance?

A

To test link aggregation performance, you would need two switches, each with at least two workstations on either end. You would have both workstations on one switch use something like FTP to transmit a large file. Each stream should have a throughput close to the max of one link, and together, should have twice that.

34
Q

How would you test link aggregation reliability?

A

To test link aggregation reliability, you would have one of the workstations ping another on the other switch, then disconnect one of the links, plug it back in, and disconnect the other. You shouldn’t lose any more than one packet.

35
Q

What network layer is responsible for providing end-to-end network reachability?

A

The Network layer (layer 3) is responsible for providing end-to-end network reachability.

36
Q

What organization is in charge of IP address assignment?

A

ICANN is in charge of IP address assignment.

37
Q

What information is contained in the IP header that relates to IP fragmentation? What does each item mean?

A

In regards to IP fragments, important information in the IP header is:
More Flag - Can be set to either M or D, “M” being “more following”, and “D” being used to show the last fragment.
Fragment Offset - 13 bits long, specifies the offset of a frame from the start of the original, unfragmented datagram.
Identification - Used to identify fragments of a datagram as parts of a whole.

38
Q

On what information is routing based on?

A

Routing is based on the destination IP address of a datagram (IP is layer 3, end-to-end, MAC is layer 2, point-to-point).

39
Q

What is IP fragmentation, and how does it work?

A

IP Fragmentation is a process by which an IP datagram is broken into several smaller pieces, called IP fragments, in order to fit through a link with a smaller maximum transmission unit (MTU). The receiving station then reassembles the fragmented datagram and passes it on to the higher layer.

40
Q

What is a maximum transmission unit?

A

Maximum transmission unit is the measure of the maximum size of a data unit that can be passed onward through a link. A larger MTU gives an increase in efficiency, but tends to increase lag and latency.

41
Q

What is CIDR, and how does it work?

A

CIDR, or Classless Inter-Domain Routing, is a method for allocating IP addresses and routing IP packets. This allows for variable-length subnet masking, aka, the creation of subnets.

42
Q

What is CIDR notation? How does it work?

A

CIDR (Classless Inter-Domain Routing) uses a notation like /24 to denote how many bits of an address take up the prefix. The /24 means that the first 24 bits are set to 1, resulting in a subnet mask of 255.255.255.0 (111111111.11111111.11111111.00000000). The remaining 8 bits can be used for IP addresses.
It’s worth remembering that two of any range of addresses in a subnet are reserved for host addresses.

43
Q

What is the Address Resolution Protocol?

A

The address resolution protocol, or ARP, is responsible for mapping from Layer 3 to Layer 2. It is a Network layer protocol that obtains the MAC address of a host, then creates a database that maps the MAC address to the host’s IP. This table is built, so that when a node broadcasts an ARP request for the corresponding MAC address to an IP, it will get it back (in an ARP reply).

44
Q

What is an ARP table?

A

An ARP table is a table built from many address resolution protocol mappings, stored locally. It’s also known as an ARP cache.

45
Q

What are the two types of entries within an ARP table?

A

There are two types of entries within an ARP table, dynamic and static. Dynamic entries are those that aren’t already in the table (prompting a broadcast). Static are those that have been manually added using the ARP utility.

46
Q

What layer does the DNS protocol belong to?

A

The DNS (domain name service) protocol belongs to the Application Layer (Layer 7).

47
Q

Which layer does the DHCP belong to?

A

DHCP (Dynamic Host Configuration Protocol) belongs to the Application Layer (Layer 7).

48
Q

If we set up a DNS server for the domain .it.ilstu.edu, we need register this DNS server to the server responsible for which domain?

A

If you were setting up a DNS server for the domain .it.ilstu.edu, you would need to register it with the server responsible for .ilstu.edu.

49
Q

What is DNS?

A

DNS is an internet protocol that’s designed to pair domain names with numeric IP addresses. Domain names operate in a hierarchy, having top level domains (such as com, edu, gov) and sub domains (like countries, co.uk). There can be further subdomains for companies (microsoft.com) and so on.
No one server is responsible for the whole namespace; it is delegated, allowing a server to cover (be authoritative) each “zone”.

50
Q

What are namespaces?

A

Namespaces are a component of DNS, and describe the entire “structure” of a DNS name. Individual domains and sub-domains, when combined into one, create a namespace.

51
Q

How do DNS queries work? Iterative queries?

A

DNS queries are handled by first having the client check its own DNS cache for the IP address needed.
If it doesn’t have it, it sends the request to one of the root DNS servers , asking for the IP of a top level domain (TLD) server for the .com/.edu/.whatever zone.
The DNS server then sends the query to the TLD server to ask for the IP of DNS server responsible for the address. If there’s multiple subdomains, the DNS server queries the other DNS server responsible for the subdomain. This repeats until the IP address is found and relayed.

52
Q

What does authoritative mean in DNS?

A

In DNS, authoritative is the term used for a DNS server being “in control” of a zone.

53
Q

What is a root hint table?

A

A root hint table is a table that contains the IP addresses of the name servers for the root domain (in DNS).

54
Q

What are zones?

A

Zones are a term within DNS referring to a domain, or a part of a domain. Each zone should have two name servers (for “resilience”, with one primary, and its updates transferred to secondary via “zone transfer”), and a name server may be authoritative for more than one zone.

Subsidiary zones can be delegated to other name servers.

55
Q

What is DHCP?

A

DHCP, or dynamic host configuration protocol, is a method by which IP addresses are automatically assigned to devices on a network without having to manually enter them.

56
Q

What are the steps within DHCP?

A

DHCP (dynamic host configuration protocol) has four steps:
Discover - The client sends a broadcast, requesting an address.
Offer - Servers send a “use this address” response.
Request - Client broadcasts that it will use the suggested address.
Acknowledge - Servers respond with “ACK” or “NAK”.

57
Q

What information is generally provided by DHCP?

A

DHCP (domain host configuration protocol) generally provides an IP address, subnet mask, DNS servers, domain, and gateway, although other things can be provided as well.

58
Q

What is a lease? How is it renewed? What happens if it expires?

A

A lease is a term within DHCP, referring to the length of time an address can be used by a particular client.
When a lease is halfway up, its client unicasts (directly sends) a Request to the server. If that server isn’t available, it will then broadcast the request. The server then sends an ACK or NAK.
If a lease expires, the client has to stop using it, and must start the process over.

59
Q

What are IP address classes?

A

IP address classes were sets of IP addresses reserved for specific organizations or groups. There are classes A-E.

60
Q

List the details of IP address class A.

A

IP address class A is the largest of all the IP address classes, and encompasses addresses with the first byte value between 1 and 127. The first byte value is set by ICANN. The other three bytes are available for use by the organization, 16 million possible IPs.

61
Q

List the details of IP address class B.

A

IP address class B encompasses addresses with the first byte value between 128 and 191. The first and second byte value is set by ICANN. The other two bytes are available for use by the organization, 65,536 possible IPs.

62
Q

List the details of IP address class C.

A

IP address class C encompasses addresses with the first byte value between 192 and 223. The first, second, and third byte value is set by ICANN. The other byte is available for use by the organization, 256 possible IPs.

63
Q

List the details of IP address class D.

A

IP address class D encompasses IP addresses with the first byte value between 224 and 239. They have no network or host ID, as the entire address is used for multicasting. Each address represents a group of hosts that listen to one sender.

64
Q

What does it mean to internetwork?

A

Internetworking refers to the crossing of multiple LAN segments and networks through a router.

65
Q

What is IP?

A

IP stands for Internet Protocol. Internet Protocol is an unreliable, connectionless protocol.

66
Q

What is an unreliable protocol?

A

An unreliable protocol is a protocol that doesn’t guarantee delivery of data.

67
Q

What is a connectionless protocol?

A

A connectionless protocol is a protocol that can service a request without starting a verified session, or guaranteeing delivery of data.

68
Q

What is the min size of the 802.11 frame body (payload)?

A

The minimum size of the 802.11 frame body is 0 bytes.

69
Q

What are the two operational modes of 802.11-based WLANs?

A

The two operational modes of 802.11-based WLANs are ad hoc and infrastructure.

70
Q

What is the ad hoc operational mode?

A

The ad hoc operational mode is an operational mode in 802.11, wherein the network does not rely on pre-existing infrastructure, instead having each node forward data for other nodes. The decision of which node forwards what is made dynamically, on the basis of network connectivity.

71
Q

What is the infrastructure operational mode?

A

The infrastructure operational mode is an operational mode for 802.11, wherein all mobile units communicate through access points, which serve as bridges to other networks.

72
Q

What wireless access method is better at supporting time-sensitive applications?

A

The wireless access method that best supports time-sensitive applications is PCF, or Point Coordination Function. This is because the coordination provided by the access point allows for certain stations to have priority.

73
Q

What is Point Coordination Function (PCF)?

A

Point Coordination Function is an access method used by 802.11, on the MAC layer. Point Coordination Function relies on using a centralized access point to coordinate the various stations’ communications to avoid collision. It uses a shorter interframe space (PIFS) than Distributed Coordination Function, and therefore is faster. However, it must be implemented on top of DCF, and runs in conjunction with it.

74
Q

What is Distributed Coordination Function (DCF)?

A

Distributed Coordination Function is an access method used by 802.11 on the MAC layer. Distributed Coordination Function requires stations that want to transmit to listen to the channel for a DIFS interval; if the channel is busy, it waits, using random backoff to ensure that multiple stations don’t constantly compete for the channel at the same time.

75
Q

What are the two main access methods used by the MAC layer in 802.11? How are they different?

A

The two main access methods used by 802.11 on the MAC layer are Distributed Coordination Function and Point Coordination Function. Point Coordination Function builds on top of Distributed Coordination Function. Distributed Coordination Function uses CSMA/CA, PCF uses Polling Access, in regards to collision avoidance.

76
Q

Why is CSMA/CD not applicable to WLAN?

A

CSMA/CD is not applicable to WLAN because 802.11 tech is half-duplex; this means that it cannot send AND listen at once, which will prevent it from detecting collisions.

77
Q

What are the control messages of 802.11 WLAN?

A

The control messages of 802.11 are:
RTS - Request to Send
CTS - Clear to Send
ACK - Acknowledgement signal to received frame
POLL - Used to poll stations for queued data in Point Coordination Function

78
Q

What is Network Allocation Vector (NAV)?

A

Network Al,location Vector is a timer that is used to inform other stations that they need to wait the specified period of time before attempting to transmit.

79
Q

What is CSMA/CA?

A

CSMA/CA stands for Carrier Sense Multiple Access / Collision Avoidance. Unlike CSMA/CD, CSMA/CA works to avoid collisions by listening to the channel to see when it is in use, and only broadcasting when it is not.

IT 377 - Practical Telecommunication Networking (4 decks)

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