networking ch5

8 bits

1 byte

Ethernet MAC address

A(n) ___________________ is a 48-bit binary value expressed as 12 hexadecimal digits (4 bits per hexadecimal digit).

IEEE requires a vendor to follow two simple rules:

All MAC addresses assigned to a NIC or other Ethernet device must use that vendor's assigned OUI as the first 3 bytes. All MAC addresses with the same OUI must be assigned a unique value in the last 3 bytes.

Organizationally Unique Identifier (OUI); unique device

All MAC addresses with the same OUI must be assigned a unique value in the last 3 bytes. a MAC address is divided into two 24 bit halves. The first 24 bits represent the and the second 24 bits represent the _______________ (network interface).

device; operating system

Depending on the and the , you will see various representations of MAC addresses. Cisco routers and switches use the form XXXX.XXXX.XXXX where X is a hexadecimal character.

multicast group IP address

Devices that belong to a multicast group are assigned a multicast group IP address. The range of IPv4 multicast addresses is 224.0.0.0 to 239.255.255.255. The range of IPv6 multicast addresses begin with FF00::/8.

Multicast group IP addresses

Devices that belong to a multicast group are assigned this

error detection

Each frame contains a trailer used to detect any errors in transmissions.

contention-based

Ethernet is a method of networking which means that any device can try to transmit data across the shared medium whenever it has data to send.

layer 2 protocols; layer 1 technologies

Ethernet standards define both the ________________ and the .

10 Mb/s 100 Mb/s 1000 Mb/s (1 Gb/s) 10,000 Mb/s (10 Gb/s) 40,000 Mb/s (40 Gb/s) 100,000 Mb/s (100 Gb/s)

Ethernet supports data bandwidths of:

Source MAC address, port number

For a switch to learn new information about addresses (memorize addresses, recognize more addresses, etc.), every frame that enters it has its _________ checked. The ________ where the frame entered the switch is also checked.

destination ip address, destination MAC address

For a unicast packet to be sent and received, a ___________ must be in the IP packet header. A corresponding ______________ must also be present in the Ethernet frame header. These 2 things combine to deliver data to one specific destination host.

Logical Link Control (LLC); MAC

For the Layer 2 protocols, as with all 802 IEEE standards, Ethernet relies on the two separate sublayers of the data link layer to operate, the Logical Link Control (LLC) and the MAC sublayers

Multicast MAC Address

The ___________________ associated with an IPv4 multicast address is a special value that begins with 01-00-5E in hexadecimal. The remaining portion of the multicast MAC address is created by converting the lower 23 bits of the IP multicast group address into 6 hexadecimal characters. For an IPv6 address, the multicast MAC address begins with 33-33.

Carrier Sense Multiple Access with Collision Detection (CSMA/CD)

The ____________________ process is used in half-duplex Ethernet LANs to detect and resolve collisions.

Addressing

The encapsulation process contains the Layer 3 PDU and also provides for data link layer addressing.

Frame delimiting

The framing process provides important delimiters that are used to identify a group of bits that make up a frame. These delimiting bits provide synchronization between the transmitting and receiving nodes.

64 and 1518 bytes

The minimum Ethernet frame size is 64 bytes and the maximum is 1518 bytes. This includes all bytes from the Destination MAC Address field through the Frame Check Sequence (FCS) field. The Preamble field is not included when describing the size of a frame.

Address Resolution Protocol (ARP)

The process that a source host uses to determine the destination MAC address is known as _____________.

multi-access bus

The underlying logical topology of Ethernet is a _ _ ; therefore, all nodes (devices) on a single network segment share the medium.

The switch updates the refresh timer for that entry

This is what happens if the source MAC address does exist in a MAC address table

The source MAC address is added to the MAC address table along with the incoming port number

This is what happens if the source MAC address is non-existent in a MAC address table

identify the actual source and destination

To prevent the excessive overhead involved in the processing of every frame, MAC addresses were created to ___________.

full-duplex switches

Today's Ethernet LANs use , which allow multiple devices to send and receive simultaneously with no collisions.

True

True or False: A layer 2 Ethernet switch uses MAC addresses to make forwarding decisions

True

True or False: A switch can have multiple MAC addresses associated with a single port. THis is common when the switch is connected to another switch.

False, 5 minutes

True or False: By default, most ethernet switches keep an entry for 30 minutes

True

True or False: 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.

False

True or False: Even when a device has an IP address that is on a remote network, the Ethernet frame can be sent directly to the destination device.

false, all but the incoming port

True or False: If the destination MAC address is a broadcast or multicast, the frame is only sent to certain ports.

True

True or False: If the source MAC address exists on the table but on a different port, the switch treats it like a new entry, replacing the old entry with the same MAC address but newer port number

False

True or False: The IP address and MAC address don't combine or work together to deliver data to one specific host in a unicast

True

True or False: When a switch has multiple MAC addresses associated with one port, commonly when the switch connects to another switch, the switch has a separate MAC address table entry for each frame received with a different source MAC address

True

True or False: many network protocols such as DCHP and ARP use broadcasts

False

True or False: you can successfully send a unicast packet even if you only have either the destination IP address or the destination MAC address but not the other

MAC address table

Unlike legacy Ethernet hubs that repeat bits out all ports except the incoming port, an Ethernet switch consults a(n) ___________ to make a forwarding decision for each frame.

Layer 2 Ethernet MAC addresses.

A Layer 2 Ethernet switch uses MAC addresses to make forwarding decisions. It is completely unaware of the protocol being carried in the data portion of the frame, such as an IPv4 packet. The switch makes its forwarding decisions based only on __________

unicast MAC address

A __________ is the unique address used when a frame is sent from a single transmitting device to a single destination device.

Source MAC Address

Although the destination MAC address can be a unicast, broadcast, or multicast address, the __________________ must always be a unicast.

be the source or destination of an ethernet frame

Any device that can must be assigned a MAC address. This includes workstations, servers, printers, mobile devices, and routers.

64; 1500; collisions or other unwanted signals

Any frame less than bytes in length is considered a "collision fragment" or "runt frame" and is automatically discarded by receiving stations. Frames with more than bytes of data are considered "jumbo" or "baby giant frames". If the size of a transmitted frame is less than the minimum or greater than the maximum, the receiving device drops the frame. Dropped frames are likely to be the result of ___________________ and are therefore considered invalid.

a corresponding Mac address

As with the unicast and broadcast addresses, the multicast IP address requires __________________ to actually deliver frames on a local network.

host-group

Because Multicast addresses represent a group of addresses (sometimes called a(n) _______ ), they can only be used as the destination of a packet. The source must always be a unicast address

multicast addresses

Because 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.

- Frame delimiting - Addressing - Error detection

Data encapsulation provides three primary functions:

subscript 16; Ethernet MAC addresses; IP Version 6 Addresses

Hexadecimal is usually represented in text by the value preceded by 0x (for example 0x73) or a subscript 16. Less commonly, it may be followed by an H(for example 73H). However, because subscript text is not recognized in command line or programming environments, the technical representation of hexadecimal is preceded with "0x" (zero X). Therefore, the examples above would be shown as 0x0A and 0x73 respectively. Hexadecimal is used to represent Ethernet MAC addresses and IP Version 6 addresses.

Destination MAC address

If the destination MAC address is a unicast address, the switch will look for a match between the __________ of the frame and an entry in its (the switch's) MAC address table

Forward the frame out the specified port

If the destination MAC address is in the MAC address table, the switch will _______

Unknown unicast

If the destination MAC address isn't in the MAC Address table, the switch will forward the frame out all ports except the incoming port. This is known as ___________

half-duplex topology using a multi-access bus

In Ethernet, every network device is connected to the same, shared media. Ethernet was once predominantly a(n) or later Ethernet hubs. This meant that all nodes would receive every frame transmitted.

Driver Software

LLC is implemented in software, and its implementation is independent of the hardware. In a computer, the LLC can be considered the _________________ for the NIC.

Multicast addresses

Multicast addresses allow a source device to send a packet to a group of devices.

ipconfig /all; ifconfig

On a Windows host, the command can be used to identify the MAC address of an Ethernet adapter. In Figure 1, notice the display indicates the Physical Address (MAC) of the computer to be 00-18-DE-DD-A7-B2. If you have access, you may wish to try this on your own computer. On a MAC or Linux host, the command is used.

communication between the upper layers and lower layers

The Ethernet LLC sublayer handles the _____________, typically between the networking software and the device hardware.

Organizationally Unique Identifier (OUI)

The IEEE assigns the vendor a 3-byte (24-bit) code, called the ____________________________________. IEEE requires a vendor to follow two simple rules All MAC addresses assigned to a NIC or other Ethernet device must use that vendor's assigned OUI as the first 3 bytes.

the Upper layers of the application

The LLC is used to communicate with ____________________, and transition the packet to the lower layers for delivery.

network protocol data

The LLC sublayer takes the , which is typically an IPv4 packet, and adds control information to help deliver the packet to the destination node.

burned-in address (BIA)

The MAC address is often referred to as a(n) ____________________ because, historically, this address is burned into ROM (Read-Only Memory) on the NIC. This means that the address is encoded into the ROM chip permanently. Today, however we can change the MAC address.

content addressable memory (CAM)

The MAC address table is sometimes referred to as a _______ table

Organizationally Unique Identifier (OUI)

The MAC address value is a direct result of IEEE-enforced rules for vendors to ensure globally unique addresses for each Ethernet device. The rules established by IEEE require any vendor that sells Ethernet devices to register with IEEE. The IEEE assigns the vendor a 3-byte (24-bit) code, called the

NIC driver

The _________ is a program that interacts directly with the hardware on the NIC to pass the data between the MAC sublayer and the physical media. MAC constitutes the lower sublayer of the data link layer; it is implemented by hardware, typically in the computer NIC. The specifics are listed in the IEEE 802.3 standards.

MAC address value

The ______________ is a direct result of IEEE-enforced rules for vendors to ensure globally unique addresses for each Ethernet device. The rules established by IEEE require any vendor that sells Ethernet devices to register with IEEE.

data encapsulation

The ______________ process includes frame assembly before transmission, and frame disassembly upon reception of a frame. In forming the frame, the MAC layer adds a header and trailer to the network layer PDU.

Multicast addresses

would be used in remote gaming, where many players are connected remotely but playing the same game. Another use is in distance learning through video conferencing, where many students are connected to the same class.

it matches the device's physical MAC address stored in RAM

When a NIC receives an Ethernet frame, it examines the destination MAC address to see if . If not, the device discards the frame. If so, it passes the frame up the OSI layers, where the de-encapsulation process takes place.

header

When the computer starts up, the first thing the NIC does is copy the MAC address from ROM into RAM. When a device is forwarding a message to an Ethernet network, it attaches header information to the frame. The ______ information contains the source and destination MAC address.

source and destination MAC address

When the computer starts up, the first thing the NIC does is copy the MAC address from ROM into RAM. When a device is forwarding a message to an Ethernet network, it attaches header information to the frame. The header information contains the _________________________________.

MAC addressing

________________ provides a method for device identification at the lower level of the OSI model. Although Ethernet has now transitioned to full-duplex NICs and switches, it is still possible that a device that is not the intended destination will receive an Ethernet frame.

media access control

____________________ is responsible for the placement of frames on the media and the removal of frames from the media. As its name implies, it controls access to the media. This sublayer communicates directly with the physical layer.

Source MAC Address

a switch dynamically builds the MAC address table by examining the _______ of frames received on a port. The switch forwards frames by searching for a match between the destination MAC address in the frame and an entry in the MAC address table

Multicast addresses

allow a source device to send a packet to a group of devices

broadcast packet

contains a destination IPv4 address that has all ones. This means all hosts on that local network will receive the packet

MAC addresses

in ethernet, different _______ are used for layer 2 unicast, broadcast, and multicast communications

Ethernet

is the most widely used LAN technology today which operates in the data link layer and the physical layer. It is a family of networking technologies that are defined in the IEEE 802.2 and 802.3 standards.

MAC Addressing

provides a method for device identification at the lower OSI layers

224.0.0.0 - 239.255.255.255

range of IPv4 multicast addresses

MAC addresses

since all the nodes received every frame in early ethernet, these were created to prevent the overload of processing every frame by identifying a frame's actual source and destination

Data Encapsulation; Media Access Control

the Ethernet MAC sublayer has two primary responsibilities:

IP config

this command is used on a MAC or Linux host to identify the MAC address of an ethernet adapter

ipconfig /all

this command is used on a windows host to identify the MAC address of an ethernet adapter

false

true or false: Since ethernet has now transitioned into full-duplex routers and switches, only the intended devices receive an ethernet frame

true

true or false: ethernet was once predominantly half-duplex topology using a multi-access bus and later hubs

true

true or false: since ethernet was predominantly a half-duplex network topology using hubs or multi-access busses, all nodes received every frame transmitted