Chapter 5 Notes

What addresses are used by the source to forwards a packet to all hosts on the network?

- Broadcast IP addresses - Broadcast MAC addresses

What are 2 variants to Cut-through switching?

- Fast-foward switching - Fragment-free switching

Address Resolution Protocol (ARP) Functions?

- Resolving IPv4 addresses to MAC addresses -Maintaining a table of mappings (called ARP table or ARP cache)

Define Hexadecimal

- a base 16 system (16 symbols) - a convenient way to represent binary values.

MAC address

- a hardware address that uniquely identifies each node on a network. -This number does not change - Similar to the name of a person. -*Known as a physical address because physically assigned to the host NIC*

Contention Based Access

-All nodes operating in half-duplex compete for the use of the medium, but only one device can send at a time. -Stattions can transmit at any time -Collisions exist -Mechanisms exist to resolve contention problems *-CSMA/CD for Ethernet networks* *-CSMA/CA for 802.11 wirless networks*

What are other names for MAC Address

-BIA - Hardware Address -Physical Address -Adapter address -Ethernet Address

Less than 64 bytes in length of the ethernt frame and size is conidered?

-Collision fragment - Runt frame

The Functions of the Layer 2 LAN Switch?

-Connects end devices to a central intermediate device on most Ethernet networks -Performs switching and filtering based only on the MAC address -Builds a MAC address table that it uses to make forwarding decisions -Uses the source MAC address of incoming frames to build the table -Table maps MAC addresses to switch ports

MAC (Media Access Control) sublayer

-Constitutes the lower sublayer of the data link layer -Implemented by hardware, typically in the computer NIC

What are the responsibilities of the MAC

-Data encapsulation (frame header and trailer) -Media access control (places and removes frames from the media)

Desribe the Ethernet Standards

-Define Layer 2 protocols and Layer 1 technologies -Two separate sub layers of the data link layer to operate - Logical link control (LLC) and the MAC sublayers

Describe Ethernet

-Family of networking technologies that are defined in the IEEE 802.2 and 802.3 standards -Supports data bandwidths of 10, 100, 1000, 10,000, 40,000, and 100,000 Mbps (100 Gbps)

LLC (Logical Link Control)

-Handles communication between upper and lower layers -Implemented in software -Identifies the layer 3 protocol carried in the frame

What are the two sublayers of the Data-link Layer?

-LLC (Logical Link Control) -MAC (Media Access Control)

What addresses deliver packet/frame to specific group of member hosts?

-Multicast IP addresses -MAC destination addresses

How does the ARP request work?

-The node that matches the IP address in the broadcast will reply -If no device responds to the ARP request, the packet is dropped because a frame cannot be created

What addresses are used by the source to forward a packet?

-Unicast IP addresses - MAC destination addresses

Define Binary

-base two (2 symbols)

Ethernet II and IEEE 802.3 standards define:

-minimum frame size as 64 bytes -maximum is 1518 bytes

Who gets Mac addresses?

-workstations servers -printers -switches -routers

How many bits in a MAC address?

48 bits

Logical IP Address

A number that uniquely identifies each computer or device connected to the Internet. - Simlar to the addres of a person -*Known as a logical address becasue assigned logically* - Assigned to each host by a network administor.

What is the purpose of ARP (Address Resoultion Protocol)?

A protocol in the TCP/IP suite used with the command-line utility of the same name to determine the MAC address that corresponds to a particular IP address.

Power over Ethernet (PoE)

A wired networking standard that allows electrical power to be sent along with data over standard Ethernet cables

What protocol is used to get a MAC address of a device when you know its IP address?

ARP (Address Resolution Protocol)

What media access control method was used by early, legacy Ethernet networks?

CSMA/CD

LAN Switch to LAN Switch?

Crossover cable

Where does Ethernet operate?

Data link layer Physical Layer

What does the *arp -a* command show?

Displays ARP cache on a PC

What does the *show ip arp* command show?

Displays ARP cache on a router

Examples of Contention based access

Ethernet Wirless

What field in a frame handles error checking?

FCS (Frame Check Sequence—contains the CRC)

What is the Layer 2 PDU?

Frame

Where is Ethernet most widely used?

LAN technonlgy

ARP request

Layer 2 broadcast (all Fs) to all devices on the Ethernet LAN -FFFF.FFFF.FFFF

What is fast-forward switching?

Lowest level of latency immediately forwards a packet after reading the destination address, typical cut-through method of switching

What type of addressing is used at Layer 2?

MAC addressing

ARP Table?

Maps IP addresses to MAC addresses

What is contained in an ARP table or ARP caches?

Maps IP addresses to MAC addresses

If destination MAC address in frame does match the device physical MAC address stored in RAM, what happens?

Matches the destination MAC of the frame, the NIC passes the frame up the OSI layers, where the decapsulation process takes place

If destination MAC address in frame does not match the device physical MAC address stored in RAM, what happens?

No match, the device discards the frame

What are MAC Addresses copied in?

RAM when the device is booted

Name a frame fowarding method on Cisco Switches?

Store-and-foward

If the destination IPv4 host is on the same local network as the source, the frame will use the MAC address of what device as the destination address?

The destination

In the event that the destination MAC address is not listed in the ARP table, what will happen?

The device sends an ARP request to retrieve the MAC address.

What happens if the ethernet frame size of a transmitted frame in less that the minimum or greater than the maximum?

The receiving device drops the frame

What is Fragment-free swithing?

The switch stores the first 64 bytes of the frame before forwarding, most network errors and collisions occur during the first 64 bytes

Latency

Time it takes for a bit to travel from its sender to its receiver.

Define decimal.

a base 10 numbering system (10 symbols)

What is Auto-MDIX?

a feature that detects Ethernet cable type

Router to computer

crossover

If the destination IPv4 host is not on the same local network as the source (on a remote network), what MAC address will be used as the destination address of the frame?

default gateway

Define cut-through switching?

fowards the frame before it is entirly receviced. -At a minimum, the destination address of the frame must be read before the frame can be fowarded.

What is MAC Addresses written in?

hexadecimal

What does the NIC show?

information to see if the destination MAC address in the frame matches the device's physical MAC address stored in RAM

4 bits equal?

nibble

What does the destintion address determine?

outgoing interface

Store-and-forward?

receives the entire frame, and computes the CRC. -If the CRC is valid, the switch looks up the destination address, which determines the outgoing interface. -The frame is then forwarded out the correct port.

What does the ARP cache timer?

removes ARP entries that have not been used for a specified amount of time

What does an Ethernet frame header contain?

source and destination MAC addresses

LAN Switch to Computer

straight-through

LAN Switch to Router

straight-through

What address is used when a device communicates with a destination on a remote network?

the device uses MAC address of its default gateway for the destination address.

ARP spoofing

uses false ARP replies to map any IP address to any MAC address

Is MAC Addresses globally unique?

yes