Networking - Chapter 5
full duplex transmission
you can transmit in both directions simultaneously, with no turnaround time
Single networks use standards at which layers?
1 (physical) and 2 (data link)
To convert 48-bit Ethernet addresses into hex notation:
1) divide the 48 bits into 4 bit units (nibbles); convert each nibble to a hexadecimal symbol; write the six symbols as six pairs with a dash between each pair
The maximum length of a data field in an Ethernet frame
1,522 octets
Ethernet transmission capacity increases in factors of:
10
Ethernet cords can be how long?
100 meters
What types of UTP wiring can carry signals 100 meters at 1 Gbps?
1000BASE-T
What type of wiring can carry 10 Gbps Ethernet 100 meters?
10GBASE-T - categories 6 and 6A
Whatever the core diameter is in fiber cable, the cladding is
125 microns
A frame is a long series of
1s and 0s
What maximum standard power does POE plus standard specify?
25 watts
How many pairs of wires are there in a UTP cord?
4
Two transmission link technologies
4-pair unshielded twisted pair (UTP) and Optical fiber
Modern multimode fiber had a core diameter of
50 microns
Most fiber cords being installed in LANs today are:
50-micron core diameter
How many wires are there in a UTP cord?
8
Which working group is likely to develop security standards to be used by multiple LAN/WAN technologies?
802.1
To thwart the ability of attackers to simply plug into any internal network companies can implement
802.1X a standard for port based access control
What term can be used interchangeably with Ethernet
802.3
Governs frame organization and switch operation in Ethernet
802.3 MAC Layer Standard
Governs the basic data link layer operation of Ethernet switches
802.3 MAC Layer Standard
The 802 working group committee that creates Ethernet Standards
802.3 Working Group
For LAN fiber, the normal wavelength is
850 nm (nanometers) because it travels far enough for typical LAN fiber distances needs and transmitters and receivers operating at this wavelength are relatively inexpensive.
What is a "state" in signaling?
A condition
electromagnetic interference (EMI)
A disturbance that can affect electrical circuits, devices, and cables due to electromagnetic conduction and possibly radiation.
Power over Ethernet (PoE) Plus
A feature that might be available on high-end wired network adapters that allows power to be transmitted over Ethernet cable to remote devices.
multimode fiber
A fiber that supports many optical waveguide modes
Address Resolution Protocol (ARP)
A protocol used to resolve an IP address to a MAC address.
working group
A standard not fully developed and adopted as an official standard recognized by IEEE.
ARP Poisoning Attack
ARP poisoning attack, some Ethernet switches flood the directed traffic to all ports of the switch, which could allow an attacker to monitor traffic not normally visible to the port where the attacker was connected, and thereby eavesdrop on VOIP traffic.
Rapid Spanning Tree Protocol (RSTP)
An Ethernet standard protocol that allows the switches within a local area network to virtually remove redundant paths between devices by eliminating loops and restoring a strict hierarchy
RJ-45 connector
An eight-position connector that uses all four pairs of wires. It is usually used for network connectivity
What kind of standard connector is used to terminate optical fiber cords?
Any type of standard connector can be used
link aggregation
As defined by the IEEE 802.3ad standard, link aggregation allows multiple physical connections to be logically bundled into a single logical connection.
Why does the number of states cause error resistance to decline?
Attenuation will have a greater effect (the range for each state is smaller)
Humans normally express EUI 48 address as
Base 16 hexadecimal (hex) notation
Why is there very low attenuation as light signals travel in optical cord?
Because of the cladding (thin glass cylinder around the core). When a light ray hits the boundary between the cord and the cladding, it is reflected back into the core (and it never enters the cladding) and so is never lost
why may link aggregation not be desirable if you will need several aggregated links to meet capacity requirements?
Because the cost may be somewhat comparable to a 10 fold increase and going to a much faster trunk line gives room for growth
Why is cross talk interference the worst at the ends of the cable?
Because the pairs of wires are untwisted and straightened to put them into an RJ-45 connector
Why can optical fibers carry light signals a long distance (much further than electrical signals can carry through UTP?
Because there is very low attenuation as light signals travel. When a light ray hits the boundary between the cord and the cladding, it is reflected back into the core (and it never enters the cladding) and so is never lost
Why is binary transmission error-resistant?
Binary only two states therefore there is less chance of miss interpretation of signals because of attenuation.
How does the ARP cache poisoning packet change the ARP cache on a victim host or router?
By sending an ARP message
What types of UTP wiring can carry signals in 10GBASE-T?
Categories 6 and 6A
Nearly all UTP cabling on the market today is what quality?
Category 5e (enhanced), category 6, or Category 6A (advanced) UTP
Ethernet has only a single standard at the ________ layer.
Data link layer. 802.3 MAC Layer standard
modal dispersion
Dispersion caused by reflected light taking paths of different lengths in an optical fiber
Observing what installation discipline will make terminal crosstalk interference a non-issue?
Do not untwist the wires more than 1.25 cm (0.5 inch)
What are Ethernet addresses called today?
EUI-48
Source and destination Ethernet addresses are
EUI-48 addresses
How many wires does a UTP have?
Eight wires organized into 4 pairs
What term can be used interchangeably with 802.3
Ethernet
Transmission speeds are governed by
Ethernet signaling standards
802.3 MAC Layer Standard
Ethernet's single MAC Layer standard. The standard that defines Ethernet frame organization and NIC and switch operation
What are RJ-45 connectors and jacks also called?
Ethernet, because ethernet is a major user of these connectors and jacks
Why does an optical fiber cord have two strands?
For full duplex transmission. You can transmit in both directions simultaneously with no turnaround time. Each strand carries the signal in one direction.
Which field in an Ethernet frame permits error detection
Frame Check Sequence Field
What determines the quality category of UTP you should use?
How fast you want to transmit
Nearly all LAN standards come from which association?
IEEE (Institute of Electrical and Electronics Engineers) Standards Association
Why is connectorization important?
If an RJ-45 connector is not placed correctly, the cord will not work properly or stop working at all. The performance degradation can be significant and difficult to diagnose.
Why is POE plus attractive to corporations?
If they are installing access points, surveillance cameras, or other infrastructure devices, they can deliver power to the devices through the Ethernet, instead of installing wiring
Is the 802.1 AE standard widely used?
Implementing authentication between each pair of devices on a network is time consuming and the ARP poisoning threat is considered so rare
Authentication Server
In Port Based Access Control, a central server that does the actual supplicant credentials checking
Where a tag fields located in an Ethernet frame if they are present?
In the Tag Protocol ID and Tag Control Information fields
Where is the packet that a MAC layer frame is delivering held in an Ethernet frame?
In the second subfield of the data field
Why may link aggregation be more desirable than installing a single faster link?
It can increase speed at an increment other than 10 and it is usually inexpensive compared to purchasing new switches
Why does multi-mode optical fiber dominate in Ethernet LANs?
It is cheaper to buy and install that single mode fiber and its transmission distances are usually fine for a LAN
Is it easy or difficult to create backup links in RSTP?
It is tricky. When a loop occurs the switches hold an election to pick a new root (top level) switch and creates a hierarchy below the root. To ensure the restored hierarchy is one the company wants to have, networking staff have to "rig the election" by setting certain parameters on each switch. This is easy if there is a single back up link but difficult if there are many back up links.
How many standards does the logical link control layer (LLC) have?
Just one
Ethernet is a switched single network and consequently, it requires standards at which layers:
Layer 1 (physical) and Layer 2 (data link)
The data link layer is divided into which sublayers?
Logical Link Control (LLC) layer and the Media Access Control (MAC) layer
What are the two components of an Ethernet Data field?
Logical link control layer (LLC) subheader and the packet the MAC layer frame is delivering
Attenuation
Loss of power in a signal as it travels from the sending device to the receiving device
Manageable switches cost more than dumb switches. Why is using them worthwhile anyway?
Lower management costs
What were Ethernet addresses originally called?
MAC addresses
How many physical layer standards does Ethernet have?
Many (such as 100BASE-TX, 1000BASE-T, and 1000BASE-SX). As electronics improve, the 802.3 working group creates new and faster physical layer standards.
The data link sublayer that governs frame design, switch operation, and other data link layer matters
Media Access Control (MAC) layer
Local area network (LAN)
Network that operates on a customer premises (home, office in a building, an entire building, a campus)
Is all digital signaling binary signaling
No
Is there a maximum end to end distance (data link distance) between pairs of hosts in an Ethernet network?
No. Switches regenerate weak signals and retransmit over another physical link. With many switches, 802.3 LANS with very large data link distances can be built.
Do optical fiber cables use RJ-45 connectors?
No. There are several standard optical fiber connectors and jacks including SC Connector, ST connectors, SC jacks and ST jacks
Do switches know the entire data link between the source and destination host? What does a switch know?
No. They only knows the information in the switching table and where to forward the frame next
UTP quality categories
Not all UTP cords have the same quality, so the wiring is labeled to describe its quality
Two dominant quality standards for multi-mode optical fiber
OM3 and OM4
Of OM3 and OM4, which quality of optical fiber carries signals further (and also cost more)
OM4
In a hierarchy, there is only _______ path between any two hosts
One. There is only one single possible path
OM
Optical multi-mode
tag field
Optional fields in an Ethernet frame that must be used if a company wishes to use priority in Ethernet to allow high priority latency intolerant applications to go first
The parties in Port Based Access Control
Peer (supplicant), Authenticator (work switch that provides the authentication service to the supplicant computer); and authentication server (does the actual supplicant credentials checking)
802.1X
Port-based access control
What type of connectors and jacks does 4-pair UTP use?
RJ-45 connectors and jacks
What standard allows backup links for redundancy in Ethernet networks
Rapid Spanning Tree Protocol (RSTP)
Why are routers expensive for the traffic volume they handle?
Routers do much more work when a packet arrives. They are connected in a mesh, so there are multiple alternative routes between two hosts. Each alternative route appears in a row in the routing table. When a packet arrives, a router must identify all possible routes and then select the best one.
What communication protocol is used with manageable switches?
SNMP (simple network management protocol)
What benefit does strong security bring for manageability?
Strong security will allow a frim to use SNMP Set commands to reconfigure switches
Using a central authentication server provides four benefits under 802.1X Port Based Access Control
Switch cost (it is less expensive than having the workgroup switch verify credentials because it minimizes the processing power needed for the switch); consistency (credentials are verified in a consistent manner); reduced management cost (credentials only need to be changed on the central authentication server when users join or leave the firm); and rapid changes (credentials can be invalidated quickly if needed)
What costs more, switches or transmission links?
Switches
Why do core switches need more processing power than workgroup switches?
Switches in the core carry the frames of many conversations. Workgroup switches only carry the conversations of the hosts they serve directly.
How do switches allow long data links despite limited physical link distances?
Switches regenerate weak signals and retransmit them over another physical link
Manageable switches
Switches that can be managed by SNMP. Cost more than non-manageable switches, but it is made up for by lower management costs
What happens when there is a failure in Rapid Spanning Tree Protocol (RSTP)
Switches will exchange messages via the RSTP protocol to agree to disable links that have failures and reactivate back up links
Address Resolution Protocol Cache
Table that lists IP addresses and their corresponding EUI-48 addresses
The 802.11 standard at the MAC Layer
The 802.11 MAC layer standard that governs how access points deal with frames and other 802.11-specific matters
802.3 Working Group
The IEEE 802 Committee that creates Ethernet standards
802.1 working group
The IEEE 802 Committee working group that creates standards used in multiple working groups, especially security standards (802.1 X and 802.1 AE)
802.11 Working group
The IEEE 802 Committee working group that creates wireless LAN standards
802 Committee
The IEEE committee responsible for all Ethernet standards.
How does a man in the middle attack benefit the attacker?
The attacker can read all transmissions between hosts on the LAN
What has led to Ethernet's dominance in LAN technology
The fact that Ethernet uses a hierarchical switch topology so there is only one single possible path between any two end hosts, making Ethernet switch forwarding simple and therefore inexpensive.
What makes Ethernet switches so inexpensive?
The fact that Ethernet uses a hierarchical switch topology so there is only one single possible path between any two end hosts, making Ethernet switch forwarding simple and therefore inexpensive.
Single points of failure
The failure of a single component can cause widespread disruption.
cladding
The glass or plastic shield around the core of a fiber-optic cable. Cladding reflects light back to the core in patterns that vary depending on the transmission mode. This reflection allows fiber to bend around corners without impairing the light-based signal.
RJ-45 Jack
The type of jack in the host or switch into which UTP cords RJ-45 connectors may plug
Authenticator
The workgroup switch verifying the peer (supplicant) in Port Based Access Control
Benefit of single mode fiber
There is no modal dispersion so it can carry signals several kilometers
How are the two wires in each pair of wires in a UTP cord organized?
They are twisted around each other several times per inch
access links
Transmission links that connect hosts to workgroup switches
In binary signaling how many possible states are there?
Two (high or low; on or off)
Ethernet cable
UTP cord (actually an inaccurate name)
To indicate quality, UTP cable is labeled with?
UTP quality categories
Observing what two limitations when installing UTP ensures that transmission quality will be good?
UTP quality categories and distance limits
How many priorities can Ethernet switches implement?
Up to 8
For what types of devices is POE Plus sufficent?
VoIP phones, surveillance cameras, and most access points. It is not enough for desktop or lap top computers.
How does a host use information in its ARP cache?
When a host wishes to transmit a packet to certain IP addresses, it looks up the IP address in the ARP table and notes the EUI-48 address for that device. It uses this EUI-48 address as the destination address in the frame that delivers the packet
terminal crosstalk interference
When untwisting wire pairs in UTP, we do not untwist more than 1.25 cm (a half inch) at their ends. This helps reduce a type of interference known as_____________.
Can ethernet switches implement priority?
Yes. They can have up to 8 priority levels.
Man in the middle attack
a hacker placing himself between a client and a host to intercept communications between them
hierarchy (hierarchical switch organization)
a switch only has one parent switch above it
core
a thin strand of glass that carry light signals in optical fiber
If you are transmitting in binary and the clock cycle is 1/1000th of second, how fast can you transmit?
a thousand bits per second
ST connector
a type of connector used in fiber optic cabling (round)
SC connector
a type of connector used in fiber optic cabling (square)
The logical link control layer (LLC) subheader
an 8 octet long subfield in an Ethernet frame data field that describes the type of packet contained in the data field
why are clock cycles necessary in signaling?
because it helps the receiver distinguish between separate signals
Why is an Ethernet network especially vulnerable if an attacker can get into a site?
because once into the network (which an attacker can do by plugging into any wall jack), the attacker bypasses the border firewall and can access anything
Two popular types of signaling
binary and digital
Of what wire characteristic is category a measure?
cable quality (UTP)
What three things do physical layer standards govern?
connectors, transmission media, and signaling
The cons of using optical fiber (versus UTP)
cost. fiber is more expensive to buy and lay than UTP
Twisting pairs of wires helps to reduce
crosstalk interference
What is the purpose of the LLC sublayer
describe the packet contained in the data field
Binary transmission is a type of
digital signaling. Not all digital signaling is binary signaling, but all transmission in a typical network can be properly called digital
Why use digital transmission
digital transmission is fairly resistant to transmission impairments
If the Frame Check Sequence Field reveals there is an error the receiver
discards the frame
The main benefit of optical fiber (versus UTP)
distance span (in contrast UTP is typically limited to runs of 100 meters)
To transmit more bits per second, the sender uses
either more states or a briefer clock cycle
binary signaling
electronic signaling in which there are two states -- high and low (or on and off) identified by 0s and 1s
digital signaling
electronic signaling where there are a few states (two or more, but not many).
802.11 MAC Layer Standard
governs how access points deal with frames and other 802.11-specific matters
What is the advantage of parallel transmission compared to serial transmission?
having four pairs of wires permits faster transmission speeds than a single wire (transmission speed increases by a factor of 4)
Ethernet LAN is organized in a
hierarchy
The traditional way to deal with single points of failure
install back up links to add redundancy
Con of single mode fiber
it is more expensive to buy and install
One general rule of thumb is that if a transmission link can span the distance between two switches,
it will not make economic sense to use an intermediate switch (switches cost more than transmission links)
modes
light rays entering the core at different angles
ethernet was created for
local area networks (LANs)
The data field in an Ethernet frame contains two subfields
logical link control (LLC) layer subheader and the packet the MAC layer frame is delivering
Longer wavelength light gives
longer transmission distances, but they are also much more expensive
microns
micrometers
Core and cladding diameters are measured in
microns (micrometers)
Limits propagation distances in multimode optical fiber
modal dispersion
light rays entering the core at different angles are called
modes
bonding
network professionals term for link aggregation
crosstalk interference
occurs when the signals of one wire affect the signals on an adjacent wire
To transmit a gigabit per second with binary signaling, each clock cycle needs to be how long?
one-billionth of a second long
single mode fiber
only the mode traveling straight can propagate through it. It has a core diameter of only 8 or 9 microns.
why is a hierarchical topology require by the Ethernet standard?
otherwise, loops would exist, causing frames to circulate endlessly from switch to another around the loop
all modern Ethernet standards specify what type of signaling?
parallel signaling
Standards that govern connectors, transmission media, and signaling
physical layer standards
The 100-meter Ethernet limit for UTP and the longer distance limits for fiber are limitations for what link?
physical links (not for end-to-end data links between hosts across multiple switches)
hierarchical topology
physical organization of switches and transmission links
To send a frame over a physical medium, the sender must convert the 1s and 0s to
physical signals
propogate
physical signals travel down transmission link to the device at the other end of the physical link
connectorization
placing an RJ-45 connector on the end of a 4-pair UTP cable
Port-based Access Control/ 802.1X standard
provides access control to prevent illegitimate clients from associating with a network. once connected to a network, the host user must prove his or her identity before the workgroup switch will pass further traffic
Redundancy increases
reliability (the probability that a host can connect)
802.1 AE
requires hosts and routers to authenticate the source of ARP messages and other messages before the receiver will accept them
Having a single possible path between end hosts in a switched Ethernet network reduces cost, but it creates
single points of failure in which the failure of a single component can cause widespread disruption
workgroup switches
switches that connect hosts to the network
core switches
switches that connect switches to other switches
If a company wishes to use priority in Ethernet, it's equipment must recognize two optional
tag fields
physical link limitations
the 100-meter Ethernet limit for UTP and the longer distance limits for fiber
What is the limiting factor on transmission speed today?
the ability of sending and receiving devices to work properly over shorter clock cycle times
wavelength
the distance between successive wave heights, troughs, starts, stops and so forth
length field
the field in an Ethernet frame that gives the length of the data field in octets using a binary number
The first optional tag field in an Ethernet frame indicates
the frame is tagged
Logical Link Control (LLC) layer
the higher of two data link layers that has functionality that all 802 standards use to interact with the internet layer
The larger UTP quality category number
the higher the quality
Frame Check Sequence Field
the last field in an Ethernet frame that permits error detection
Media Access Control (MAC) layer
the lower of the two data link sublayers with functionality specific to a particular working group's core operation. Every working group has a single standard at this level.
reliability
the probability that a host can connect
amplitude
the strength of a light signal (how hard the wave will hit you)
Peer
the supplicant in Port Based Access Control
the second optional tag field in an Ethernet frame indicates
the tagged information
The minimum length of a data field in an Ethernet frame
there is no minimum length
4-pair unshielded twisted pair (UTP)
transmission link technology that carries electrical signals over copper wire pairs
optical fiber
transmission link technology that carries light signals through very think glass tubes
trunk lines
transmission links that connect switches to other switches
serial transmission
transmitting over a single pair of wires; transmission of 1 bit per clock cycle
parallel transmission
transmitting with more than one pair of wires carrying transmission bits; transmission of 1 bit per clock cycle per wire pair
State two installation disciplines that will reduce UTP transmission problems to negligibility?
twisting the wires and when untwisting them, do not untwist them for more than 1.25 cm (0.5 inch)
In digital signaling, the number of states is always a multiple of:
two (2.4.8.etc)
What type of copper wiring is widely used in Ethernet?
unshielded twisted pair wiring
Maximum distance of UTP in LANs
usually 100 meters
Light propogates as a
wave
clock cycle
when a device transmits, it holds the signal constant for a brief period of time
The work of the 802 committee is done in
working groups
