Chapter 5 Ethernet
Transcript Chapter 5 Ethernet
Intro to Routing & Switching
completion of this chapter, you should
be able to:
Describe the operation of the Ethernet sublayers.
Identify the major fields of the Ethernet frame.
Describe the purpose and characteristics of the
Ethernet MAC address.
Describe the purpose of ARP.
Explain how ARP requests impact network and
Explain basic switching concepts.
Compare fixed configuration and modular
Configure a Layer 3 switch.
widely used LAN technology
2 layers does it operate at?
Data link & physical
are the 2 sublayers of the data link?
LLC & MAC
Helps communicate with network layer
Adds control info
Performs it in software
Adds MAC addresses
Adds error detection to frame
Placing the frames on the media
is a logical bus; physical star
Signal passes to all
Can send whenever
Can be collisions
Ethernet is contention-based/non-deterministic
Data contends or shares for a spot on the media
Doesn’t know when it’ll get access to it
Listens for signal on media
No signal = transmit data
Transmit at same time= collision
Devices do not keep track of whose turn it is
More collisions= less throughput
SOLUTION: CSMA/CD & CSMA/CA
Silence= transmit data
devices transmit at same time, collision
Backoff random time, listen for silence,
detection not a problem much
Using switches & full-duplex, this is not a
Sends Ready to Send message to AP
Gets a Clear to Send message from AP
to identify frame
Each host has a unique address
Burned into NIC hardware
/ 12 hex digits / 6 bytes
1st 24 bits OUI; 2nd 24 bits serial #
many bits is a MAC address?
is the OUI in this MAC?
does a wireless network use to avoid
sublayer places the frames on the
OUI is how many bytes?
shares access to the media. It
contends for the media and does not take
turns transmitting. Not taking turns means
the network is…
the MAC address found in hardware or
End of Day One
frame size is 64 bytes; max is 1522 bytes
Data is 46-1500 bytes
64 bytes is considered a collision fragment
& will be dropped
important addresses are encapsulated
into a frame?
Source & destination MAC
does the preamble used for?
is the minimum frame size?
happens if a frame is less than 64
Considered a fragment & dropped
many bits in a MAC address?
first 6 hex digits are what?
many hex digits?
OUI would then be the 1st ____ bytes.
sublayer is used to communicate with
the upper layers?
32 bits, 4 octets
8 bits in each octet
in each octet from 0-255
That’s a total of 256 numbers.
up the values of the binary 1’s
Hexadecimal (Base 16)
0-9, A-F (10-15)
16 total #’s
with a 0x
to one communication
to all in a network
Dest. MAC address will be all F’s
DHCP & ARP use broadcasts
to a group in a network
Remote gaming or video conference
Dest. IP will be 184.108.40.206 -220.127.116.11
Dest. MAC will begin with 01-00-5E
kind of message gets sent from one PC
to a group within a network?
each as unicast, multicast, or
Burned into NIC (DOES NOT CHANGE)
Similar to the name of a person
Similar to the address of a person
Based on where the host is actually located
Both the physical MAC & logical IP addresses are
required for a computer to communicate just
like both the name and address of a person are
required to send a letter
IP NEVER changes!
Source & Destination MAC changes at each
do you change your MAC address?
Get a new NIC
or F. The destination IP address changes
happens to the source & destination
MAC addresses as you go from router to
router across the Internet?
They change (router port substituted)
is a layer 2 address?
is IEEE 802.3?
is IEEE 802.2?
is a layer 3 address?
table of IP/MACs
Added from communication
Added from ARP requests
have the dest. IP, not the MAC
ARP request is all F’s where?
is an ARP request sent?
replies to the ARP request?
Only one with matching dest. IP
Router# show ip arp
you want to access a remote server, and
you don’t have the destination MAC, what
gets substituted for it?
The default gateway’s MAC address
router has ports with MAC addresses. How
do you view the router’s ARP table?
Router#sh ip arp
does ARP find? What do you know?
Finds the dest. MAC; you know the dest. IP
It’s a broadcast. If many devices started at same
time, there’d be a flood of ARP requests which
would cause a reduction in performance for a
short period of time.
ARP poisoning (or spoofing)
Attacker forges MAC address to have frames
delivered to different computer
Use a switch
network into smaller collision
Replies go to one device only
Implement security too
duplex, Half duplex, Auto
Must match setting of device
Half duplex uses CSMA/CD to avoid collisions
uses cut-through switching
As soon as destination MAC is read, it forwards
Lowest latency; in and out
Store first 64 bytes before forwarding
Most errors & collision happen there (runts)
If it makes it through, should be error-free
switches connect to each other. One port is
100Mbps and the other is 1000Mbps. What
speed will that connection operate at?
feature will allow you to use a straightthrough cable to connect two switches
switch port is connected to a hub with 3
computers on it. How many MAC addresses
will be in the table for that port?
Do it at least 4 times
Different scenario each time
network from MAC address table
Fixed Configuration Switch
Connected by special cable to act as one switch
Fixed may be stackable
PoE (Power over Ethernet)
As is; no add-ons or changing
A 24 port switch will always be 24 ports
Delivers power to a device, like an IP phone
We use this in school
More $$, faster forwarding rate
type of switch can you add a card to
add more Ethernet ports or add fiber ports?
bought a 24 port switch and cannot add
more ports to it. What kind of switch did you
have the switch above and need more
ports. You then buy more 24 port switches
and connect them with a special cable. What
kind of switch do you now have?
Fixed & stackable
Combined with router functions
like a switch
in router functions
Knows which IP addresses are out each port too
an Ethernet port a routed port
To connect to the ISP
Configure a port
have we configured with an IP on a
IP for remote management
This is similar
a Layer 3 Switch
address(es) does a layer 2 switch read?
address(es) does a layer 3 switch read?
IP & MAC
want to connect your Layer 3 switch to
your ISP instead of using a regular router.
What must you configure one of the ports as?
command enables the routing function
on a switch port?
the study guide handout
the quiz on netacad.com
In this chapter, you learned:
Ethernet is the most widely used LAN technology
Ethernet standards define both the Layer 2
protocols and the Layer 1 technologies.
The Ethernet frame structure adds headers and
trailers around the Layer 3 PDU to encapsulate
the message being sent.
As an implementation of the IEEE 802.2/3
standards, the Ethernet frame provides MAC
addressing and error checking.
Using switches in the local network has reduced
the probability of frame collisions in half-duplex
The Layer 2 addressing provided by Ethernet
supports unicast, multicast, and broadcast
Ethernet uses the ARP to determine the MAC
addresses of destinations and map them against
known IP addresses.
Each node on a network has both a MAC address
and an IP address.
The ARP protocol resolves IPv4 addresses to MAC
addresses and maintains a table of mappings.
A Layer 2 switch builds a MAC address table that
it uses to make forwarding decisions.
3 switches are also capable of
performing Layer 3 routing functions,
reducing the need for dedicated routers on a
Layer 3 switches have specialized switching
hardware so they can typically route data as
quickly as they can switch.
Intro to Routing & Switching