Module 6 & 7 study guide Fund of data communication.

MAC

A layer 2 Ethernet switch uses Layer 2 _________ addresses to make forwarding decisions.

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.

Describe the features of an Ethernet broadcast.

All end systems are chained to each other and terminated in some form on each end. Infrastructure devices such as switches are not required to interconnect the end devices. Legacy Ethernet networks were often bus topologies using coax cables because it was inexpensive and easy to set up.

Bus

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 is the MAC address of the destination device NIC.

Destination MAC address

NO

Does full-duplex communications with Ethernet switches require access control through CSMA/CD?

Wireless

Ethernet is one of two LAN technologies used today. What is the other?

a unique 6 hexadecimal (i.e., 24-bit or 3-byte) code

Explain what a organizationally unique identifier (OUI) is.

Offers the lowest level of latency. Immediately forwards a packet after reading the destination address. Because it 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. It is the typical cut-through method of switching.

Fast-forward switching

The switch stores the first 64 bytes of the frame before forwarding. Can be viewed as a compromise between store-and-forward switching and fast-forward switching. The reason it stores only the first 64 bytes of the frame is that most network errors and collisions occur during the first 64 bytes. It 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. It 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

Both ends of the connection can send and receive simultaneously.

Full-duplex

Both devices can simultaneously transmit and receive on the shared media. The data link layer assumes that the media is available for transmission for both nodes at any time. Ethernet switches operate in full-duplex mode by default, but they can operate in half-duplex if connecting to a device such as an Ethernet hub. Click play in the figure to see the animation showing full-duplex communication.

Full-duplex communication

Only one end of the connection can send at a time.

Half-duplex

Both devices can transmit and receive on the media but cannot do so simultaneously. WLANs and legacy bus topologies with Ethernet hubs use the half-duplex mode. Half-duplex allows only one device to send or receive at a time on the shared medium. Click play in the figure to see the animation showing half-duplex communication.

Half-duplex communication

Subscript.

Hexadecimal may also be represented by a ___________, or the hex number followed by an H.

0x

Hexadecimal numbers are often represented by the value preceded by _______ to distinguish between decimal and hexadecimal values in documentation.

This is a WAN version of the star topology in which a central site interconnects branch sites through the use of point-to-point links. Branch sites cannot exchange data with other branch sites without going through the central site.

Hub and smoke

Hexadecimal

IPv6 addresses and Ethernet addresses are represented using the ___________________ base sixteen number system.

Decimal Binary

In networking, IPv4 addresses are represented using the _______ base ten number system and the __________ base 2 number system.

Twisted pair Fiber-optic Coaxial

List the wire types or media Ethernet uses to communicate over.

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.

Logical Link Control (LLC)

Refers to the way a network transfers frames from one node to the next. This topology identifies virtual connections using device interfaces and Layer 3 IP addressing schemes.

Logical topology

Data Link

MAC addressing provides a method for device identification at the ________ ______ layer of the OSI model.

Implements this sublayer (IEEE 802.3, 802.11, or 802.15) in hardware. It is responsible for data encapsulation and media access control. It provides data link layer addressing and it is integrated with various physical layer technologies.

Media Access Control (MAC)

This topology provides high availability but requires that every end system is interconnected to every other system. Therefore, the administrative and physical costs can be significant. Each link is essentially a point-to-point link to the other node.

Mesh

full-duplex.

Most Cisco switches and Ethernet NICs default to autonegotiation for speed and duplex. Gigabit Ethernet ports only operate in?

Identifies the physical connections and how end devices and intermediary devices (i.e, routers, switches, and wireless access points) are interconnected. The topology may also include specific device location such as room number and location on the equipment rack. Physical topologies are usually point-to-point or star.

Physical topology

This is the simplest and most common WAN topology. It consists of a permanent link between two endpoints.

Point-to-point

End systems are connected to their respective neighbor forming a ring. The ring does not need to be terminated, unlike in the bus topology. Legacy Fiber Distributed Data Interface (FDDI) and Token Ring networks used ring topologies.

Ring

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

MAC address table.

Switches dynamically build ________________ by examining the source MAC address of the frames received on a port.

Data link and Physical

What OSI layers does Ethernet operate in?

*Header *Data *Trailer

What are the three basic parts of a data link layer frame?

Collisions will occur.

What happens if two devices on a half duplex connection transmit at the same time?

BIA (burned-in address)

What is another name for a MAC address?

Use its assigned OUI as the first 6 hexadecimal digits. Assign a unique value in the last 6 hexadecimal digits.

When a vendor assigns a MAC address to a device or Ethernet interface, what must the vendor include?

Hexadecimal

When using _________________, leading zeros are always displayed to complete the 8-bit representation.