Exploring the TCP/IP Link Layer Flashcards
To connect a switch to a LAN, you must use some sort of media. The most common LAN media is Ethernet. Ethernet is not just a type of cable or protocol. It is a network standard published by the Institute of Electrical and Electronics Engineers
Institute of Electrical and Electronics Engineers (IEEE)
Specifies a transmission speed of 1000 Megabits per second (Mbps) or 1 Gigabit per second (Gbps)
1000
Refers to baseband signaling (which means that only Ethernet signals are carried on the medium)
BASE
Represents twisted-pair cabling
T
Type of wiring in which two conductors are twisted together for the purposes of canceling electromagnetic interference (EMI) from external sources.
Twisted-pair cabling
Copper cabling for short and medium-length distances because of its low cost, when compared to fiber-optic or coaxial cable.
unshielded twisted-pair (UTP)
Capable of transmitting data at speeds of up to 100 Mbps
Category 5
Used in networks running at speeds of up to 1000 Mbps (1 Gbps)
Category 5e
Comprises four pairs of 24-gauge copper wires, which can transmit data at speeds of up to 10 Gbps
Category 6
Used in networks running at speeds of up to 10 Gbps
Category 6a
Used in networks running at speeds of up to 10 Gbps
Category 7
Used in networks running at speeds of up to 40 Gbps
Category 8
Describes systems which pass electric power along with data on Ethernet cabling.
Power over Ethernet (PoE)
Cables are primarily used for connecting electrically unlike devices.
Straight-through cables
Used for connecting electrically like devices.
Crossover cables
Enabled on an interface, the interface automatically detects the required cable connection type (straight through or crossover) and configures the connection appropriately.
medium-dependent interface crossover (auto-MDIX)
A flexible, transparent fiber that is made of very pure glass (silica) and is not much larger than a human hair. It acts as a waveguide, or “light pipe,” to transmit light between the two ends of the fiber.
optical fiber
Is used for shorter distances at a lower bit rate than SMF
MMF (Multi-Mode Fiber)
For long-distance communications,
SMF (Single-Mode Fiber)
Is for enterprise equipment and is commonly used on small form-factor pluggable (SFP) modules.
Local connector (LC)
Is for enterprise equipment.
Subscriber connector (SC)
Is for patch panels (for their durability)
Straight tip (ST)
Is for patch panels and is used by service providers.
Fiber-optic connector (FC)
Connector is a two-fiber connector (transmit and receive), has a form factor and is used for enterprise equipment.
Mechanical Transfer Registered Jack (MT-RJ)
This field consists of 8 bytes of alternating 1s and 0s that are used to synchronize the signals of the communicating computers.
Preamble
The DA field contains the MAC address of the network interface card (NIC) on the local network to which the frame is being sent.
Destination Address (DA)
The SA field contains the MAC address of the NIC of the sending computer.
Source Address (SA)
This field contains a code that identifies the network layer protocol.
Type
This field contains the network layer data. If the data is shorter than the minimum length of 46 bytes, a string of extraneous bits is used to pad the field. This field is also known as “data and padding”.
Payload
The frame check sequence (FCS) field includes a checking mechanism to ensure that the frame of data has been transmitted without corruption. The checking mechanism that is being used is the cyclic redundancy check (CRC).
FCS (frame check sequence)
Communication in which a frame is sent from one host and is addressed to one specific destination. In a unicast transmission, there is only one sender and one receiver. Unicast transmission is the predominant form of transmission on LANs and within the Internet.
Unicast
Communication in which a frame is sent from one address to all other addresses. In this case, there is only one sender, but the information is sent to all the connected receivers. Broadcast transmission is used for sending the same message to all devices on the LAN.
Broadcast
Communication in which information is sent to a specific group of devices or clients. Unlike broadcast transmission, in multicast transmission, clients must be members of a multicast group to receive the information.
Multicast
The OUI identifies the manufacturer of the NIC. The IEEE regulates the assignment of OUI numbers. Within the OUI, there are 2 bits that have meaning only when used in the destination address field:
24-bit OUI
When the least significant bit in the first octet of the MAC address is 1, it indicates to the receiving interface that the frame is destined for all (broadcast) or a group of (multicast) end stations on the LAN segment. This bit is referred to as the Individual/Group (I/G) address bit.
Broadcast or multicast bit
The second least significant bit of the first octet of the MAC address is referred as a universally or locally (U/L) administered address bit. Normally, the combination of the OUI and a 24-bit station address is universally unique. However, if the address is modified locally, this bit should be set to 1.
Locally administered address bit
This portion uniquely identifies the Ethernet hardware.
24-bit, vendor-assigned, end-station address
The MAC address table is stored in the
content-addressable memory (CAM)
The switch examines the destination MAC address and if it is unicast, performs one of the following actions depending whether the MAC address is present in the MAC address table:
- No: Forwards the frame out all ports except the incoming port (referred to as unknown unicast).
- Yes: Forwards the frame out of the port from which that MAC address was learned previously.
Unicast frames forwarding
The switch examines the destination MAC address and if it is broadcast or multicast, forwards the frame out all ports except the incoming port (unless using Internet Group Management Protocol (IGMP) with multicast, in which case it will only send the frame to specific ports).
Broadcast or multicast frames forwarding
