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105 Cards in this Set
- Front
- Back
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What are the two problems we face with building protocols at the physical layer?
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Propagation Delay and Limited Bandwidth
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What is framing at the physical layer?
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Detecting errors on pieces of the whole data
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What is flow control and the physical layeR?
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We don't want senders overwhelming receievers
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What is vampire tapping?
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The old way they used to connect wires and computers together
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What is time division multiplexing?
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Chopping up time units for each computer to transmit
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What is frequency division multiplexing?
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Chopping up the frequencies for the different computers to use
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What are two examples of statitc bandwidth allocation schemes?
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TDM and FDM
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What are the problems with circuit switched networks?
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There is a dedicated connection between all hosts
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What are the problems with packet switched networks?
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Multiplexing. Different bandwidths between hosts. Ordering of packets
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What are the different layers of data communications?
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Physical. Datalink. Network. Transport. Application
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What are the requirements we might want from our network?
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Reliability. Availability. Security, Global connectivity. Scalability. Transparency. QOS guarantees(Throughput. Bound on loss. Bound on delay. Bound on jitter) Accounting. Usable(think DNS) Manageble. Interoperable. Hetergeneous.
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What does UDP add to IP?
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UDP adds data checksum and best effort service
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What does TCP add to IP?
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Data checksum and reliable byte-stream delivery PLUS flow and congestion control.
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What is the simplest analog signal?
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Sine wave
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What are the three ways we can encode data into a sine wave?
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Frequency, amplitude, and phase
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What is baud?
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Changes per second to detect
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Is it possible to have infinite bandwidth?
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No.
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What is bandwidth?
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The range of frequencies
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Who found the fundamental limit to the signaling rate?
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Nyquist 1924
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What is the highest signaling rate?
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2H the bandwidth
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What is the H in Nyquists formula?
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H = bandwidth
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How do you find bitrate?
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2H log base 2 of l
H=bandwidth l = number of levels |
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What is attenuation?
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The face that the strength of the signal dies with distance
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What is the problem with amplifying the signal?
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You also amplify the noise
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What is delay distortion?
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The fact that higher frequencies travel faster than lower frequencies
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What kinds of noise can we get at the physical layer?
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Thermal noise, electron agitation
Cross talk |
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What did claude shannon determine to be the capacity of a medium?
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C = Hlog2(1+ s/n ratio)
C = capacity, H = bandwidth |
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What is pulse code modulation?
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Take a continuous signal and puts it through a sampler and gives a digital version
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How many twists do cat3 and cat5 have?
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Cat3 - 3-4 twists per foot
Cat5 - 3-4 twists per inch |
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What are packets called at the datalink layer?
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Frames
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What is bit stuffing?
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If I am encoding and I see 5 consecutive 1's I add a 0. If I ever see 6 1's I know I am done.
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How do we deteremine effeciency of a frame rate transmission?
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N = Tf/Tf+2Tau+Ta+Tp
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What is wrong with stop and wait at the datalink level?
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We are limited to one frame at a time?
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How do windowing protocols work at the datalink level?
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We can send x number of frames at a time without an ack. The window shrinks from the left and expands from the right.
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What are the fundamental rules for decoding at the datalink level?
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If there is an error I always want to detect it. If there is no error I want to believe it.
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What is a codeword at the datalink layer?
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A legal sequence of bits (any combo of n-bits that are legal)
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When would we ever use error correction at the datalink layer?
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If we are talking over really long distances, eg. to Mars, and we don't want to have to retransmit.
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What is ARQ?
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Auto Repeat Request
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What is FEC
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Foreign Error Correction
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What is MAC
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Medium Access Control
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What is the Aloha protocol?
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Transmt when you are ready. Listen to channel after you transmit. If collision is detected delay t and retransmit.
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What is CSMA?
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Carrier Sense Multiple Access
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What is CSMA/CD?
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Carrier Sense Multiple Access with Collision Detection
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What does CSMA/CD add to CSMA?
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It checks to see if people are talking while I am talking
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At what point do you know you have seized the medium?
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At 2 tau you know without a doubt you are the only one talking
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In a token ring, when can you talk?
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When you receive a token
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What is the number of the Ethernet protocol?
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802.3
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What is thicknet
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10base5 - 10 mbps 5 base freq's 500m max distance
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What is thin net
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10base2
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What is twisted pair
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10base-T (500m)
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What is the physical longest length of an ethernet medium?
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2500M
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What does padding help insure?
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That we have a transmission time of at least 2 tau
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What does ethernet use as its way of making sure everyone gets a chance to talk?
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P-Persistent CSMA/CD
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What is DQDB?
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Distributed Queue Dual Bus
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What is MAN?
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Metro Area Network
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What is a repeater at datalink layer?
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Everything is sent to both networks
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What is a selective repeater
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Things are sent to all networks unless the repeater knows where the host is
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What is a repeater called at the Transport layer?
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A bridge
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What is a transparent bridge?
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Plug it in and it works. Repeats stuff it needs to not stuff it don't.
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What is backward learning?
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Learn about the network from where things came from.
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What are the options for an IP packet?
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Record route, source routing(strict and loose) security info, timestamp
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What are the two routing categories?
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Direct and Indirect
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What is ARP?
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Address Resolution Protocol
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What is RARP?
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Reverse Address Resolution Protocol
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What is ICMP?
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Internet Control Message Protocol
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What protocol does a smurf attack use?
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ICMP
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How do you get a network ID from a subnet mask?
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AND it with your ip address and out pops your network id
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What is VLSM?
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Variable Length Subnet Mask
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What is CIDR?
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Classless Interdomain Routing
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What is UDP?
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User Datagram Protocol
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What is TCP?
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Transmission Control Protocol
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What is the TCP URG flag do?
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The urgent pointer is valid. The urgent pointer is the number of octets from the beginning of the segment to last urgent byte
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What is the TCP PSH flag?
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Pushes it all the way to the app (last segment of a write)
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What is the TCP RST flag?
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Reset; if things go wrong, dump the connection
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What is the TCP window size multiplier?
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The window size field is not big enough for us to have significant window sizes so we multiply our window size with this field
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What does the pseudoheader do?
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The pseudoheader is put on before the packet is sent to calculate the checksum
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How many sequence numbers do ACK's consume?
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0
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What is the MSL of a TCP packet?
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2 minites
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What is MSL?
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Maximum Segment Lifetime or Length
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What is time wait in TCP?
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If you send a fin before you see one you are going to end up in time wait
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How do you calculate the RTT of a TCP packet?
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RTT = alpha(RTTold) + (1-alpha)M
where M is the most recent packet |
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If a TCP packet times out what is the new transmission timeout?
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2 times the old one
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What are two types of flow control?
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Fixed sliding window and Credit Based Scheme
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What is Nagle's algorithm?
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When data comes in, first byte is sent.
All subsequent bytes are buffered til ack is recived. |
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What types of protocols is Nagle's algorithm not appropriate for?
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RDP, telnet, ssh
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What is silly window syndrome?
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When you have a window size of 1.
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How do you avoid silly window syndrome?
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Avoid receiver sending credits of small octets
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What implies that there is congestion in the network?
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Packet loss
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How do we do congestion control in TCP?
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First we do slow start to the slow start threshold then additive increase after we hit that threshold. The slow start threshold is cut in half with a packet loss.
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What is ATM?
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Asynchronous Transfer Mode
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What is CBR, VBR, and ABR
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Constant Variable and Available
Bit Rate |
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What is APIPA?
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Automatic Private IP Addressing
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When do you APIPA?
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You APIPA when you can't find a DHCP server
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What are Internet root servers?
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Servers that resolve TLD's
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What is a TLD?
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Top Level Domain
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What is TTL?
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Time To Live
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What are the classes of networks in the resource records of the internet
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SOA,A,MX,NS,CNAME,PTR,HNFO,TXT
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What are the two types of DNS
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Recursive and Non Recursive
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What does the TTL in a DNS server tell us?
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How long the cache is good for
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What is an authoritative vs. non authoritative response from DNS?
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Non authoritative is when a server tells us an ip address but it is not the root dns server for that domain name
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What program can we use to look up DNS information from the command line?
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nslookup
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Which protocol does DNS almost always run over?
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DNS
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What are the 4 problems we are worried about when implementing security into our networks?
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Interception. Interruption. Modification. Fabrication.
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What are the two types of security attacks and give examples?
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Passive attacks-eavesdropping, traffic analysis
Active attacks-everything else |
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What is SSL?
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Secure Socket Layer
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