Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
59 Cards in this Set
- Front
- Back
What is the data link layer responsible for |
Allowing upper layers to access media Prepare network data for physical network Exchange frames BTW nodes over physical network |
|
What layer performs error detection |
Data link |
|
What are the two sublets of data link |
LLC logical link control MAC Media access control |
|
What does the LLC do |
Upper sublayer Communicates with the network layer Allows multiple layer 3 protocols to use the same network interface and media. |
|
What are some layer 3 protocols |
Ipv4 and 6 |
|
What does media access control do |
Lower sub layer Defines media access process performed by hardware. |
|
Technique used to get frames on and off the media |
Media Access Control Method |
|
What layer governs how to format a frame for use on different media |
Data link layer |
|
At each hop along the path, a router does what to the frame. 4 steps |
Accepts a frame from a medium DE encapsulates the frame RE encapsulates the packet into new frame Forwards frame to next segment of the network. |
|
What layer is responsible for controlling the transfer of frames across media |
Data link |
|
Example of changing frames across network. |
A router changing ethernet frames to WiFi frames. |
|
Media Access Control sublayer is the frame equivalent to |
Traffic rules. |
|
WANS are connected with these 3 physical topologies |
Point to point HUB and Spoke Mesh |
|
Point to point topology |
A permanent link between two endpoints. |
|
Hub and spoke topology |
A cent site interconnects branch sites using point to point |
|
Mesh topology |
Every end system is connected to every other end system. Each link is a point to point link to other node |
|
What is a virtual circuit |
A point to point connection BTW two nodes even if they aren't in the same physical location |
|
What is half duplex |
Both devices can transfer and receive on media but not at the same time |
|
What does CSMA/CD stand for |
Carrier sense multiple access/collision detection |
|
When is cmsa/CD used |
Used in half duplex |
|
Explain the CSMA/CD process |
Pc 1 wants to send ethernet frame to pc 3 Pc 1's NIC checks for traffic on network, if none, sends frame. If other device wants to send but is receiving frames, it must wait. All other devices will receive the frame but ignore it if it's not for them. |
|
What happens when a collision occurs |
Both devices will detect collision(known as CD) Done by NIC noticing higher signal amplitude or comparing data transferred to data sent. |
|
What is CA collision avoidance |
Doesn't detect collisions but tries to avoid by waiting before transmitting. Waits to receive ACK that a transmission is done on network |
|
What are the 3 things included in a frame |
Header Data Trailer |
|
What are frame start and stop indicator flages |
ID the beginning and end limits of frame |
|
Frane fields included in the header of a frame |
Frame start Addressing Type Control |
|
Frane fields included in the trailer of a frame |
Error detection Frane stop |
|
How to determine MAC address of a node knowing only the IP address |
Broadcast ARP query packet with the IP The right compt replies to node with MAC The node saves MAC in ARP table until it becomes old (TTL time to live) |
|
What layers does ethernet operate in |
Data link Physical layer |
|
Name each part of the ethernet frame. 6 parts |
Preamble Destination address Sure address Ethernet type Data plus pad FCS |
|
Ethernet frane: preamble |
Used to alert stations that data is being transmitted. |
|
Ethernet frame: type |
Indicates higher layer protocol Most likely IP |
|
Ethernet frame: FCS |
Detects errors. Uses CRC cycle redund check Checked at receiver, if error detected, frame dropped |
|
Min and max ethernet frame size |
64 bytes min 1518 max |
|
Why is ethernet unreliable |
It's conectionless (no handshaking) It doesn't send ACKs or to sending NIC |
|
What does the 802.2 header and data do |
Uses pad to increase frame field to at least 64 bytes |
|
Start of frame delimiter |
Syncs sending and receiving devices for frane delivery |
|
Frame field how big is the length |
2 bytes |
|
What does CSMA do if it detects another transmission while transmitting |
Aborts and sends jam signal Then enter exponential back off (random number) |
|
What is a jam signal |
Makes sure all other transmitters are aware of collision. |
|
What is a collision domain |
Where data packets can collide with one another being sent on a shared medium |
|
What happens when a switch does not have the destination address I'm it's ARP table |
It floods it out to all ports |
|
Frame forwarding method: store and forward |
Switch receives the entire frame. It computes the CRC. If valid it looks up destination address, determines the outgoing interface and forwards it to correct port. |
|
Frame forwarding: cut through |
This switch forwards frane before it's entirely received. At minimum the destination address must be read before sent. |
|
What is a switch |
Link layer device Store and forward ethernet frames |
|
Can a switch forward more than one frame at a time |
Yes because each port can make forwarding decisions |
|
What does a switch do |
Learns which hosts can be reached through which interfaces by receiving frames from that destination |
|
Purpose of layer 2 switches |
Segment broadcast domains into separate collision domains |
|
How do VLANS work |
They are created on a switch and act as 2 different switches No communication BTW LANS |
|
How to share data between LANS |
With a router |
|
What standard allows devices from different vendors to communicate |
IEEE 802.1q |
|
What does a layer 3 switch do |
Allows for routing between VLANS |
|
What is ppp and how does it work |
Point to point protocol data link control One sender one receiver one link Just needs error detection and packet framing |
|
What is a CAM table |
Contains a list of MAC addresses available on a port of a switch. |
|
How to do a CAM table overflow attack |
Attacker floods a switch with large amount of flash source MAC addresses until table fills up. When full switch floods all ports on a VLANS it's connected to. |
|
How to prevent cam overflow |
Make any invalid mac address be blocked or shut down the port they are using. |
|
What does ARP do |
Maps IP address to MAC |
|
What is an ARP attack |
When ARP table is nodded by attacker with false info allowing for address spoofing. To perform mitm or dos attack |
|
What does the physical layer standard IEEE cover |
Ethernet Wireless Bluetooth |