Chapter 7 - Ethernet Switching
features of an Ethernet multicast are as follows:
....
Therefore, the Ethernet MAC address of that device would be
00-60-2F-3A-07-BC.
What is a function of the MAC sublayer? ( three.)
1. Controls access to media, 2. checks for errors in received bits, 3. uses CSMA/CD or CSMA/CA
what data bandwidth does ethernet support
10, 100, 1000, 10,000, 40,000, 100,000 mbps 1, 10, 40, 100 gbps
Hexadecimal may also be represented by a subscript
16, or the hex number followed by an H (e.g., 73H).
The range of IPv4 multicast addresses .
224.0.0.0 to 239.255.255.255.
Ethernet MAC address is a
48-bit address expressed using 12 hexadecimal digits, as shown in the figure
Ethernet MAC address consists
6 hexadecimal vendor OUI code followed by a 6 hexadecimal vendor-assigned value
The process that a source host uses to determine the destination MAC address associated with an IPv4 address is known as
Address Resolution Protocol (ARP).
Which part of an Ethernet Frame uses a pad to increase the frame field to at least 64 bytes?
Data Field
Which part of an Ethernet Frame describes the higher-layer protocol that is encapsulated?
EtherTpye
? is one of two LAN techs while the other is Wireless LANS (WLANS)
Ethernet
Any device that is the source or destination of an Ethernet frame, will have
Ethernet NIC and therefore, a MAC address. This includes workstations, servers, printers, mobile devices, and routers.
Data encapsulation
Ethernet frame, ethernet addressing ,ethernet Error detection
When using hexadecimal, leading zeroes are always displayed to complete the 8-bit representation.
For example, in the table, the binary value 0000 1010 is shown in hexadecimal as 0A.
Which part of an Ethernet frame detects errors in the frame?
Frame check sequence
ethernet is a family of networking techs where is it defined
IEEE 802.2 and 802.3 standards
LLC sublayer
IEEE 802.2 sublayer communicates between the networking software at the upper layers and the device hardware at the lower layers.
Accessing the media
IEEE 802.3 MAC sublayer includes the specifications for different Ethernet communications standards over various types of media including copper and fiber.
Cisco needs to assign a unique MAC address to a new device.
IEEE has assigned Cisco a OUI of 00-60-2F. Cisco would then configure the device with a unique vendor code such as 3A-07-BC.
multicast MAC address is associated with, and uses addressing information from,
IPv4 or IPv6 multicast address.
Which data link sublayer controls the network interface through software
LLC
Which data link sublayer works with the upper layers to add application information for delivery of data to higher level protocols?
LLC
Layer 2 Ethernet switch uses
Layer 2 MAC addresses to make forwarding decisions. It is completely unaware of the data (protocol) being carried in the data portion of the frame, such as an IPv4 packet, an ARP message, or an IPv6 ND packet.
In Ethernet, different MAC addresses are used for
Layer 2 unicast, broadcast, and multicast communications.
The process that a source host uses to determine the destination MAC address associated with an IPv6 address is known as
Neighbor Discovery (ND).
Which part of an Ethernet Frame notifies the receiver to get ready for a new frame?
Preamble
When a device is forwarding a message to an Ethernet network, the Ethernet header includes these:
Source MAC address, Destination MAC address
Ethernet Addressing
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.
Frame Check Sequence Field
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.
Preamble and Start Frame Delimiter Fields
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.
Type / Length
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.
Source MAC Address Field
This 6-byte field identifies the originating NIC or interface of the frame.
Destination MAC Address 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.
Data Field
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.
Destination MAC address
This is the MAC address of the destination device NIC.
Source MAC address
This is the MAC address of the source device NIC.
Ethernet frame
This is the internal structure of the Ethernet frame
MAC sublayer
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.
When a vendor assigns a MAC address to a device or Ethernet interface, the vendor must do as follows
Use its assigned OUI as the first 6 hexadecimal digits. Assign a unique value in the last 6 hexadecimal digits.
a host with IPv4 address 192.168.1.5 (source) requests a web page from the server at IPv4 unicast address 192.168.1.200 For a unicast packet to be sent and received,
a destination IP address must be in the IP packet header.
Ethernet multicast frame is received and processed by
a group of devices on the Ethernet LAN that belong to the same multicast group
unicast MAC address is the unique
address that is used when a frame is sent from a single transmitting device to a single destination device.
CSMA/CD
allows multiple devices to share the same half-duplex medium, detecting a collision when more than one device attempts to transmit simultaneously. It also provides a back-off algorithm for retransmission.
frames with more than 1500 bytes of data
considered "jumbo" or "baby giant frames".
Frame less than 64 bytes in length
considered a "collision fragment" or "runt frame" and is automatically discarded by receiving stations.
Ethernet MAC address
consists of a 48-bit binary value.
convert between decimal and hexadecimal values
convert the decimal or hexadecimal value to binary, and then to convert the binary value to either decimal or hexadecimal as appropriate.
what is the MAC sublayer
data encapsulation and accessing the media.
what does the MAC provide
data link layer addressing and is integrated with various physical layer technologies.
where does ethernet operate
data link layer and physical layer
Ethernet NICs will also accept frames if the
destination MAC address is a broadcast or a multicast group of which the host is a member.
If there is no match,
device discards the frame
If the encapsulated data is an IP multicast packet,
devices that belong to a multicast group are assigned a multicast group IP address.
Hexadecimal numbers are often represented by the value preceded by 0x (e.g., 0x73) to
distinguish between decimal and hexadecimal values in documentation.
Hexadecimal is used to identify
ethernet address because a single hexadecimal digit represents four binary bits
In an Ethernet LAN
every network device is connected to the same, shared media
When a NIC receives an Ethernet frame,
examines the destination MAC address to see if it matches the physical MAC address that is stored in RAM.
range of IPv6 multicast addresses begins with
ff00::/8. Because multicast addresses represent a group of addresses (sometimes called a host group), they can only be used as the destination of a packet. The source will always be a unicast address.
MAC addressing provides a method
for device identification at the data link layer of the OSI model.
computer boots up, the NIC copies its MAC address
from ROM into RAM.
Ethernet Error detection
he Ethernet frame includes a frame check sequence (FCS) trailer used for error detection.
binary 00000000 to 11111111 can be represented in
hexadecimal as the range 00 to FF, as shown in the next figure.
IPv6 addresses and Ethernet addresses are represented
hexadecimal base sixteen number system
where does LLC place information
in the frame that identifies which network layer protocol is being used for the frame
If there is a match,
it passes the frame up the OSI layers, where the de-encapsulation process takes place.
what does the ethernet standards define
layer 2 protocols, and layer 1 techs data link layer and physical layer protocals
Dropped frames
likely to be the result of collisions or other unwanted signals. They are considered invalid.
Ethernet use Data Link Sublayers
logical link control (LLC) and Media access control (MAC)
Frame size
may be larger if additional requirements are included, such as VLAN tagging
Ethernet frame
minimum Ethernet frame size is 64 bytes and the expected maximum is 1518 bytes. This includes all bytes from the destination MAC address field through the frame check sequence (FCS) field.
possible for duplicate MAC addresses to exist because of
mistakes made during manufacturing, mistakes made in some virtual machine implementation methods, or modifications made using one of several software tools
with the unicast and broadcast addresses,
multicast IP address requires a corresponding multicast MAC address to deliver frames on a local network.
Routing protocols and other network protocols use
multicast addressing
Applications such as video and imaging software may also use
multicast addressing, although multicast applications are not as common.
what does that allow
multiple Layer 3 protocols, such as IPv4 and IPv6, to use the same network interface and media.
Preamble Field
not included when describing the size of the frame
hexadecimal numbering system uses
numbers 0 to 9 and the letters A to F.
corresponding destination MAC address must also be
present in the Ethernet frame header. The IP address and MAC address combine to deliver data to one specific destination host.
If size of frame less than the minimum or greater than the maximum
receiving device drops the frame
Ethernet frame fields
refer to the function of each field
what doe ethernets today use
switches that operate in full-duplex. Full-duplex communications with Ethernet switches do not require access control through CSMA/CD.
The switch makes its forwarding decisions based solely on
the Layer 2 Ethernet MAC addresses.
MAC address is referred to as a burned-in address (BIA) because
the address is hard coded into read-only memory (ROM) on the NIC means that the address is encoded into the ROM chip permanently.
The MAC address is used to identify
the physical source and destination devices (NICs) on the local network segment.
responsibility of the vendor to ensure that none of its devices be assigned
the same MAC address.
what are the wired communications for ethernet
twisted-pair, fiber-optic links, and coaxial cables
all vendors that sell Ethernet devices must register with the IEEE to obtain
unique 6 hexadecimal (i.e., 24-bit or 3-byte) code called the organizationally unique identifier (OUI).
MAC addresses must be
unique to the Ethernet device or Ethernet interface.
On modern PC operating systems and NICs, it is possible to change the MAC address in software
useful when attempting to gain access to a network that filters based on BIA.
Ethernet over a half-duplex medium
uses a contention-based access method, carrier sense multiple access/collision detection (CSMA/CD) This ensures that only one device is transmitting at a time.
Legacy Ethernet
using a bus topology or hubs, is a shared, half-duplex medium.
48-bit Ethernet MAC address can be expressed
using only 12 hexadecimal values.
Jumbo frames
usually supported by most Fast Ethernet and Gigabit Ethernet switches and NICs.
