Ethernet Flashcards
Original designer of Ethernet
Robert Metcalfe and Xerox
Which layer is Ethernet
Layer 2 of OSI model (MAC addressing), Layer 1 OSI model (signaling)
Data encapsulation primary functions
Framing: group of bits making up a frame
Addressing
Error detection: CRC
Ethernet cables used today
UTP Copper and optical fiber
First versions of Ethernet used…
Coax cable
10BASE5
aka Thicknet; used a thick coaxial; cabling distance up to 500 m
10BASE2
aka Thinnet; smaller in diameter and more flexible than Thicknet
Hubs…
Take a group of nodes and allow the network to see them as a single unit; only one station could transmit at a time (half-duplex communication)
Switches…
only send frame only to its proper destination port (if it’s known) = full-duplex communication
Gigabit Ethernet
used to describe Ethernet implementations that provide bandwidth of 1000 Mbps (1 Gbps) or greater
Characteristic(s) of Ethernet MAC addresses
a 48-bit or 64-bit binary value expressed as 12 hexadecimal digits; use ipconfig/all
01-23-45-67-89-AB
Special value of Multicast addresses
01-00-5E
Detecting collisions on devices
all devices can detect an increase in the amplitude of the signal above the normal level causing a JAM SIGNAL
Response to JAM signal
invokes a backoff algorithm to all devices to stop transmitting for a random amount of time, allowing collisions to subside
Preamble
situation where a collision has not occurred during half duplex mode and the sending device transmits 64 bits of synchronization
Asynchronous communication
Ethernet with speeds of 10 Mbps and slower; required timing info to synchronize the receive circuit to the incoming data and then discard the 8 bytes.
Synchronous communication
timing info not required
In order for CSMA/CD to operate….
the sending device must become aware of a collision before it has completed transmission of a minimum-sized frame
Slot time
longer than the theoretical amount of time required to travel between the furthest points of the collision domain, collide with another transmission at the last possible instant, and then have the collision fragments return to the sending station and be detected
most commonly observed data for a jam signal is..
a repeating 1, 0, 1, 0 pattern, the same as the Preamble
Four data rates currently defined for operation over optical fiber and TP:
10BASE5, 10BASE2, 10BASE-T (using cat3/cat5 UTP), 100Mbps - Fast Ethernet
Transmission pairs of UTP
1,2 = transmitting 3,6 = receiving
1000BASE-T characteristics
Provides full-duplex transmission using all four pairs in Category 5 or later UTP cable
Latency
time it takes a signal to reach all destinations on the media. Increasing the length of the media increases latency
Collision domain
any part of the network where packets from two or more nodes can interfere with each other
Switch increases throughput of network by…
A dedicated bandwidth to each port
Collision-free environment
Full-duplex operation
Ethernet LAN switch five basic functions:
Learning: Switch examines source MAC address
Aging: MAC entries are timestamped
Flooding: floods all ports if destination MAC address is unknown
Selective Forwarding
Filtering: does not forward a frame to the same port in which it arrived
ARP protocol
Resolves IPv4 addresses to MAC addresses
Maintains a cache of mappings
ARP process
- When ARP receives a request to map an IPv4 address to a MAC address. it looks for the cached ARP address in its table.
- It sends a broadcast (ARP request) to discover the MAC address of the destination device on the local network
Proxy ARP
useful for when a host might send an ARP request seeking to map an IPv4 address outside of the range of the local network
ARP cache of requesting device will contain the MAC address associated with the IPv4 address of the gateway.
ARP spoofing
A technique used by an attacker to inject the wrong MAC address association into a network by issuing fake ARP requests.
