CITN 220 Chapter 7
automatic medium-dependent interface crossover (auto-MDIX)
(auto-MDIX)
frame is received and processed by a group of devices on the Ethernet LAN that belong to the same multicast group.
Ethernet multicast frame
two variants of cut-through switching
Fast-forward switching Fragment-free switching
Which part of an Ethernet frame detects errors in the frame?
Frame Check Sequence
Both ends of the connection can send and receive simultaneously.
Full-duplex
The features of an Ethernet broadcast are as follows:
It has a destination MAC address of FF-FF-FF-FF-FF-FF in hexadecimal (48 ones in binary). It is flooded out all Ethernet switch ports except the incoming port. It is not forwarded by a router.
Which two types of memory buffering techniques are used by switches?
Port based memory buffering Shared memory buffering
Frames are stored in queues that are linked to specific incoming and outgoing ports. A frame is transmitted to the outgoing port only when all the frames ahead in the queue have been successfully transmitted. It is possible for a single frame to delay the transmission of all the frames in memory because of a busy destination port. This delay occurs even if the other frames could be transmitted to open destination ports.
Port-based memory
Which part of an Ethernet Frame notifies the receiver to get ready for a new frame?
Preamble
The Preamble (7 bytes) and Start Frame Delimiter (SFD), also called the Start of Frame (1 byte), fields are used for synchronization between the sending and receiving devices. These first eight bytes of the frame are used to get the attention of the receiving nodes. Essentially, the first few bytes tell the receivers to get ready to receive a new frame.
Preamble and Start Frame Delimiter Fields
This 6-byte field identifies the originating NIC or interface of the frame.
Source MAC Address Field
What feature automatically negotiates the best speed and duplex setting between interconnecting devices?
autonegotiation
Which function or operation is performed by the LLC sublayer?
it communicates with upper protocol layers
two functions or operations are performed by the MAC sublayer?
it is responsible for media access control it adds a header and trailer to form an OSI layer 2 PDU
Which two characteristics describe Ethernet technology?
it uses unique MAC addresses to ensure that data is sent to the appropriate destination it is supported by ieee 802.3 standards
What will a host on an Ethernet network do if it receives a frame with a unicast destination MAC address that does not match its own MAC address?
it will discard the frame
What addressing information is recorded by a switch to build its MAC address table?
the source layer 2 address of incoming frames
is the unique address that is used when a frame is sent from a single transmitting device to a single destination device.
unicast Mac Address
The features of an Ethernet multicast are as follows:
-There is a destination MAC address of 01-00-5E when the encapsulated data is an IPv4 multicast packet and a destination MAC address of 33-33 when the encapsulated data is an IPv6 multicast packet. -There are other reserved multicast destination MAC addresses for when the encapsulated data is not IP, such as Spanning Tree Protocol (STP) and Link Layer Discovery Protocol (LLDP). -It is flooded out all Ethernet switch ports except the incoming port, unless the switch is configured for multicast snooping. -It is not forwarded by a router, unless the router is configured to route multicast packets.
What is the special value assigned to the first 24 bits of a multicast MAC address transporting an IPv4 packet?
01-00-5E
Ethernet operates in the data link layer and the physical layer. It is a family of networking technologies defined in the IEEE 802.2 and 802.3 standards. Ethernet supports data bandwidths of the following:
10 Mbps 100 Mbps 1000 Mbps (1 Gbps) 10,000 Mbps (10 Gbps) 40,000 Mbps (40 Gbps) 100,000 Mbps (100 Gbps)
What are the two sizes (minimum and expected maximum) of an Ethernet frame?
1518 bytes 64 bytes
what does a layer 2 switch use to make forwarding decisions.
A Layer 2 Ethernet switch uses Layer 2 MAC addresses to make forwarding decisions.
This frame forwarding method forwards the frame before it is entirely received. At a minimum, the destination address of the frame must be read before the frame can be forwarded.
Cut-through switching
This field (46 - 1500 bytes) contains the encapsulated data from a higher layer, which is a generic Layer 3 PDU, or more commonly, an IPv4 packet. All frames must be at least 64 bytes long. If a small packet is encapsulated, additional bits called a pad are used to increase the size of the frame to this minimum size.
Data Field
Which part of an Ethernet Frame uses a pad to increase the frame field to at least 64 bytes?
Data Field
This 6-byte field is the identifier for the intended recipient. As you will recall, this address is used by Layer 2 to assist devices in determining if a frame is addressed to them. The address in the frame is compared to the MAC address in the device. If there is a match, the device accepts the frame. Can be a unicast, multicast or broadcast address.
Destination MAC Address Field
This is the MAC address of the destination device NIC
Destination MAC address
The Ethernet frame includes both a source and destination MAC address to deliver the Ethernet frame from Ethernet NIC to Ethernet NIC on the same LAN.
Ethernet Addressing
The Ethernet frame includes a frame check sequence (FCS) trailer used for
Ethernet Error Detection
IEEE 802.3 data encapsulation includes the following:
Ethernet Frame, Ethernet Addressing, Ethernet Error Detection
Which part of an Ethernet Frame describes the higher-layer protocol that is encapsulated?
Ethernet Type
frame is received and processed by every device on the Ethernet LAN.
Ethernet broadcast frame
This is the internal structure of the Ethernet frame
Ethernet frame
offers the lowest level of latency. Fast-forward switching immediately forwards a packet after reading the destination address. Because fast-forward switching starts forwarding before the entire packet has been received, there may be times when packets are relayed with errors. This occurs infrequently, and the destination NIC discards the faulty packet upon receipt. In fast-forward mode, latency is measured from the first bit received to the first bit transmitted. Fast-forward switching is the typical cut-through method of switching.
Fast-forward switching
the switch stores the first 64 bytes of the frame before forwarding. Fragment-free switching can be viewed as a compromise between store-and-forward switching and fast-forward switching. The reason fragment-free switching stores only the first 64 bytes of the frame is that most network errors and collisions occur during the first 64 bytes. Fragment-free switching tries to enhance fast-forward switching by performing a small error check on the first 64 bytes of the frame to ensure that a collision has not occurred before forwarding the frame. Fragment-free switching is a compromise between the high latency and high integrity of store-and-forward switching, and the low latency and reduced integrity of fast-forward switching.
Fragment-free switching
The Frame Check Sequence (FCS) field (4 bytes) is used to detect errors in a frame. It uses a cyclic redundancy check (CRC). The sending device includes the results of a CRC in the FCS field of the frame. The receiving device receives the frame and generates a CRC to look for errors. If the calculations match, no error occurred. Calculations that do not match are an indication that the data has changed; therefore, the frame is dropped. A change in the data could be the result of a disruption of the electrical signals that represent the bits.
Frame Check Sequence Field
Only one end of the connection can send at a time.
Half-duplex
This IEEE 802.2 sublayer communicates between the networking software at the upper layers and the device hardware at the lower layers. It places information in the frame that identifies which network layer protocol is being used for the frame. This information allows multiple Layer 3 protocols, such as IPv4 and IPv6, to use the same network interface and media.
LLC Sublayer
Which data link sublayer controls the network interface through software drivers?
Logical Link Control LLC
Which data link sublayer works with the upper layers to add application information for delivery of data to higher level protocols?
Logical Link Control LLC
This sublayer (IEEE 802.3, 802.11, or 802.15 for example) is implemented in hardware and is responsible for data encapsulation and media access control. It provides data link layer addressing and is integrated with various physical layer technologies.
MAC Sublayer
Deposits all frames into a common memory buffer shared by all switch ports and the amount of buffer memory required by a port is dynamically allocated. The frames in the buffer are dynamically linked to the destination port enabling a packet to be received on one port and then transmitted on another port, without moving it to a different queue.
Shared memory
This is the MAC address of the source device NIC.
Source MAC address
This frame forwarding method receives the entire frame and computes the CRC. CRC uses a mathematical formula, based on the number of bits (1s) in the frame, to determine whether the received frame has an error. If the CRC is valid, the switch looks up the destination address, which determines the outgoing interface. Then the frame is forwarded out of the correct port.
Store-and-forward switching
Which network device has the primary function to send data to a specific destination based on the information found in the MAC address table?
Switch
Which network device makes forwarding decisions based on the destination MAC address that is contained in the frame?
Switch
is true about MAC addresses?
The first 3 bytes are used by the vendor assigned OUI
What happens to runt frames received by a Cisco Ethernet switch?
The frame is dropped
What statement describes a characteristic of MAC addresses?
They must be globally unique
This 2-byte field identifies the upper layer protocol encapsulated in the Ethernet frame. Common values are, in hexadecimal, 0x800 for IPv4, 0x86DD for IPv6 and 0x806 for ARP.Note: You may also see this field referred to as EtherType, Type, or Length.
Type / Length
Can a Switch have more than one mac address associated with a port.
Yes (A switch can have multiple MAC addresses associated with a single port. This is common when the switch is connected to another switch. The switch will have a separate MAC address table entry for each frame received with a different source MAC address.)
What is auto-MDIX?
a feature that detects ethernet cable type
What type of address is 01-00-5E-0A-00-02?
an address that reaches a specific group of hosts
What is a function of the MAC sublayer?
controls acces to the media checks for errors in recieved bits uses csma/cd or csma/ca to support ethernet technology
Which switching method can be implemented using fast-forward switching or fragment-free switching?
cut-through switching
What are two methods for switching data between ports on a switch?
cut-through switching store and forward switching
