3.5-Network Adapters

Network Adapters or NIC can help transmit and receive data over a network. Adapters are architecture-specific.

Adapter Transmission Medium

Network adapters are specific to their transmission medium

Ex. Computers > NIC > Transceiver >>> Converts signals into either electrical/analog signals

• SFPs/Modems/Switches/Routers act on the Layer 1 of the OSI Model (Physical).
• NICs operate on both Layer 1 and 2 of the OSI Model (Physical and Data-Link Layer)
• MAC addresses function at Layer 2 (Data Link) to communicate with other devices on the network

Adress Resolution Protocol (ARP)

• At Layer 3 (Network), packet is created containing IP Addresses.
• At Layer 2 (Data Link), packet is turned into frames which contains MAC address of the destination device, source address, and packet.

ARP determines a device's MAC address from a known IP address.

Frame is stripped and then the packet is reviewed.

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Suppose you have two computers on the same network. Computer A needs to send data to computer B. The data is created in the upper OSI Model layers and needs to go down through the layers to the other computer.

At Layer 3 of the OSI Model, a packet is created that includes the destination IP address, the source IP address, and the data that's being sent. The packet is converted into a frame at Layer 2. The frame contains the MAC address of the destination device, the address the source device, and the packet.

Suppose this computer has an IP address of 1.1.1.1, and this computer has an IP address of 1.1.1.2. Computer A already knows Computer B's IP address, but it doesn't know its MAC address. When the source computer creates the frame, it uses its own MAC address as the source address. Since it doesn't know the destination device's MAC address, it needs to find it. The computer does this using the address resolution protocol (ARP).

ARP is used to determine a device's MAC address from a known IP address. It does this by creating a special frame with its own source address and the broadcast MAC address. The broadcast MAC address is a MAC address with all values set to F. The broadcast address is placed in the destination address of the ARP frame.

The ARP frame is sent to all computers on the local network segment. When the destination computer receives the frame, it looks at the destination MAC address. Because the MAC address is a broadcast address (all Fs) it needs to process the frame to see what's inside.

The computer strips off the frame headers and looks at the packet. The packet's destination IP address matches this computer's IP address, so the computer knows that it needs to process the packet and respond to it.

This computer responds to the packet by sending its MAC address to the source computer. Another packet is created and sent to the source computer.

Now that the source computer has the destination computer's MAC address, it can send the data it originally wanted to by adding the previously unknown destination MAC address to the frame.

After a computer or device learns the MAC address of a destination device on the network, it saves that MAC address in the ARP table so that it can use it in the future.

Using ARP, devices on a network can obtain the MAC address of other devices that have a known IP address. In cases when the MAC address is known but the IP address isn't, a protocol known as reverse ARP is used. And it's sometimes called RARP.

[tip] Remember that network adapters function at both Layer 1 and Layer 2 of the OSI model, while transceivers and media converters operate only at Layer 1.

Network Adapter Facts

Network Interface Card (NIC) Features

The following are a few features of network interface cards.

• The network interface card is responsible for converting binary data into a format that can be sent on the network medium.
  • A transceiver is responsible for converting digital data into digital signals to be sent on the medium.
    • The type of signal the transceiver sends depends on the type of network. A fiber optic NIC sends light signals, a wired NIC sends electronic signals on a wire, and a wireless NIC sends radio signals.
    • To receive signals, the transceiver converts digital signals from the network to digital data for the PC.
  • A modem converts binary data to analog waves on the sending end (modulation) and then converts the analog waves back to binary data on the receiving end (demodulation).
• Some computers, such as laptops, come with built-in NICs. Other computers use NICs that plug in to the system's expansion slots or are external to the computer and connect through an existing computer port.
• Network interface cards are Layer 1 devices because they send and receive signals on the network medium. They are also Layer 2 devices because they must follow the rules for media access and because they read the physical address in a frame.
• The type of network interface card you choose must match the network architecture you are connecting to.
• Older network interface cards used an external transceiver to connect to the network media. However, all modern network interface cards use a built-in transceiver.

Network Interface Card Components

Component	Description
Transceiver module	A transceiver module is used to change the media type of a port on a network device, such as a switch or a router. The following are the most common types of transceiver modules: A gigabit interface converter (GBIC) is a large transceiver that fits in a port slot and is used for gigabit media, including copper and fiber optic.- A small form-factor pluggable (SFP) is similar to a GBIC, but is a smaller size. An SFP is sometimes called a mini-GBIC.- SFP+ is a newer version of the SFP. SFP+ supports data rates as high as 10 Gbit/s, 8 Gbit/s Fiber Channel, 10 gigabit Ethernet, and the Optical Transport Network (OTU2 standard).- A 10 gigabit small form-factor pluggable (XFP) transceiver is similar to an SFP in size, but is used for 10 gigabit networking.- Quad (4-channel) SFP is a compact hot-pluggable transceiver that is also used for data communication applications.
Media converter	You use a media converter to connect network interface cards that are using different media types. For example, a media converter could be used to connect a server with a fiber optic Ethernet NIC to a copper Ethernet cable. Media converters work at the Physical layer (Layer 1). Media converters do not read or modify the MAC address in any way.- Media converters convert one media type to another within the same architecture (such as Ethernet). A media converter cannot translate between two different architectures. This must be done using a bridge or a router. Converting from one architecture to another requires modifying the frame contents to modify the Data Link layer address.
Media access control (MAC) address	A MAC address is a unique identifier burned into the ROM of every Ethernet NIC. The MAC address is a 12-digit (48-bit) hexadecimal number (each number ranges from 0–9 or A–F).- The address is often written as 00-B0-D0-06-BC-AC or 00B0.D006.BCAC. Dashes, periods, and colons can be used to divide the MAC address parts.- The MAC address is globally unique by design. The first half of the MAC address, the first six digits, is assigned to each manufacturer. The manufacturer determines the rest of the address, assigning a unique value that identifies the host address. A manufacturer that uses all the addresses in the original assignment can apply for a new MAC address assignment.- Devices use the MAC address to send frames to other devices on the same subnet.- Some network cards allow you to change the MAC address through jumpers, switches, or software, but there are few legitimate reasons for doing so.
Address Resolution Protocol- (ARP)	Hosts use ARP to discover the MAC address of a device from its IP address. Before two devices can communicate, the MAC address of the receiving device must be known. If the MAC address isn't known, ARP does the following to find it: The sending device sends out a broadcast frame. The destination MAC address is all Fs (FFFF:FFFF:FFFF).- The sending MAC address is its own MAC address.- The destination IP address is the known IP address of the destination host.- The sending IP address is its own IP address.- - All hosts on the subnet process the broadcast frame, looking at the destination IP address.- If the destination IP address matches its own address, the host responds with a frame that includes its own MAC address as the sending MAC address.- The original sender reads the MAC address from the frame and associates the IP address with the MAC address, saving it in its cache.- Once the sender knows the MAC address of the receiver, it sends data in frames addressed to the destination device. These frames include a cyclic redundancy check (CRC) that is used to detect frames that have been corrupted during transmission.- Hosts use the reverse address resolution protocol (RARP) to find the IP address of a host with a known MAC address.