Welcome!
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Feel free to say hello in the chat
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© 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 1
Etiquette Reminder
Chat rules and etiquette during class
While it is great to connect before class begins in the chat space and I encourage
that …
During class please only use the chat space for posting questions or trying to
answer a question (from myself or classmate) – I very much encourage that as it is
a great way to learn
• Otherwise, questions get lost in the chatter and the incessant posting is a distraction
while talking/listening
© 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 2
INFO-1280
Theory Assessments:
Theory Component (on campus)
Test #1
Monday Feb. 10th 9-11am (10%)
Test #2
Monday March 31st 9-11am (20%)
Final Exam – Exam week (20%)
• Refer to college exam schedule when available
Tests/exams are on campus, not online
Room booking will be posted when available 3
Michael McNorgan 2020
INFO-1280
Practical Assessments:
Practical (in-class lab assignments) Component
Lab Assignment #1 (5%)
• Week of January 27th
Lab Assignment #2 (10%)
• Week of February 24th
Lab Assignment #3 (15%)
• Week of March 24th
Lab Assignment #4 (20%)
• Friday April 11th
• Monday April 14th
• Wednesday April 16th
The actual day/time is your regular lab day/time for that week.
This is not a take home assignment; it is completed in lab on the equipment. 4
Michael McNorgan 2020
Module 7: Ethernet Switching
Introduction to Networks v7.0
(ITN)
Module Objectives
Module Title: Ethernet Switching
Module Objective: Explain how Ethernet works in a switched network.
Topic Title Topic Objective
Explain how the Ethernet sublayers are related to the frame
Ethernet Frame
fields.
Ethernet MAC Address Describe the Ethernet MAC address.
Explain how a switch builds its MAC address table and
The MAC Address Table
forwards frames.
Describe switch forwarding methods and port settings
Switch Speeds and Forwarding Methods
available on Layer 2 switch ports.
© 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 6
7.1 Ethernet Frames
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Ethernet Frames
Ethernet Encapsulation
• Ethernet operates at the data link layer and the physical layer.
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Ethernet Frames
Data Link Sublayers (Review)
The 802 standards, including Ethernet, use two separate sublayers
© 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 9
Ethernet Frames
MAC Sublayer
The MAC sublayer is responsible for data encapsulation and accessing the media.
Data Encapsulation
IEEE 802.3 data encapsulation includes the following:
1. Ethernet frame - This is the internal structure of the Ethernet frame.
2. Ethernet Addressing - The Ethernet frame includes both a source and destination MAC address
to deliver the Ethernet frame from Ethernet NIC to Ethernet NIC on the same LAN.
3. Ethernet Error detection - The Ethernet frame includes a frame check sequence (FCS) trailer
used for error detection.
© 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 10
Ethernet Frames
Ethernet Frame Fields
• Describe the purpose and information within the fields of an Ethernet frame
© 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 11
Ethernet Frames
Ethernet Frame Fields
• Describe the purpose and information within the fields of an Ethernet frame
© 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 12
Ethernet Frames
Ethernet Frame Fields
• Describe the purpose and information within the fields of an Ethernet frame
© 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 13
7.2 Ethernet MAC Address
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Ethernet MAC Addresses
Ethernet MAC Address
An Ethernet MAC address consists of a 6-hexadecimal vendor OUI code followed by a 6-hexadecimal
vendor-assigned value.
© 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 15
Ethernet MAC Addresses
Ethernet MAC Address
• Because MAC addresses must be unique and IEEE manages the OUI portion of the MAC
addresses Wireshark can display vendor name as part of MAC addresses
• https://www.wireshark.org/tools/oui-lookup.html
• https://regauth.standards.ieee.org/standards-ra-web/pub/view.html#registries
© 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 16
Ethernet MAC Addresses
Frame Processing
Discuss how devices process Ethernet frames.
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Ethernet MAC Addresses
Unicast MAC Address
Discuss a unicast transmission at layer 2
Video 7.2.4
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Ethernet MAC Addresses
Broadcast MAC Address
Discuss a broadcast transmission at layer 2
Video 7.2.5
What are the similarities and differences between
unicast and broadcast messages?
© 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 19
Ethernet MAC Addresses
Multicast MAC Address
Discuss a multicast transmission at layer 2
Video 7.2.6
Compare and contrast multicast messages with unicast
and broadcast messages.
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7.3 The MAC Address Table
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The MAC Address Table
Switch Fundamentals
• A Layer 2 Ethernet switch uses MAC addresses to make forwarding decisions.
• An Ethernet switch examines its MAC address table to make a forwarding decision for
each frame
• When a switch is turned on, the MAC address table is empty
• Switches are unaware of the data (protocol) being carried in the data field of the
frame, such as an IPv4 packet, an ARP message, or an IPv6 ND packet.
Note: The MAC address table is sometimes referred to as a content addressable memory
(CAM) table.
© 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 22
The MAC Address Table
Switch Learning and Forwarding
Examine the Source MAC Address (Learn)
Switches can learn about MAC addresses automatically or statically.
This process is unique to the source MAC address in the Ethernet header.
Find the Destination MAC Address (Forward)
Switches search for a match between the destination MAC address of the frame and an
entry in its MAC address table. If destination MAC address is in the table, then forward
frame out specific port. If the destination MAC address is not in the table, then forward the
frame out all ports except the incoming port.
Note: If the destination MAC address is a broadcast or a multicast, the frame is also
flooded out all ports except the incoming port.
© 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 23
The MAC Address Table
Switch Learning and Forwarding
Activity Switch It! 7.3.6
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7.4 Switch Speeds and
Forwarding Methods
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Switch Speeds and Forwarding Methods
Frame Forwarding Methods on Cisco Switches
Discuss different frame forwarding methods between network ports/interfaces.
• Store-and-forward switching - Accepts the entire frame before looking up the destination
address to determine the outgoing interface.
• Cut-through switching - This frame forwarding method forwards the frame before it is entirely
received. At a minimum, the destination address of the frame must be read before the frame can
be forwarded.
• Fast-forward switching - lowest latency because forwards frame after reading the destination address.
• Fragment-free switching - ensures a collision has not occurred by reading the first 64 bytes of the frame before
forwarding.
© 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 26
Switch Speeds and Forwarding Methods
Memory Buffering on Switches
Discuss buffering techniques to store frames before forwarding them. Buffering may also be used if
the destination port is busy because of congestion.
• Port-based memory
• Frames are stored in queues that are linked to specific incoming and outgoing ports
• Frame is removed from queue and transmitted to outgoing port only when all frames ahead in the queue
have been successfully transmitted
• Possible for single frame waiting on a busy destination port to delay all other frames, even if other frames
could be transmitted to open destination port
• Shared memory
• Deposits all frames into common memory buffer shared by all switch ports
• Frames in buffer dynamically linked to destination port, so frame can be received on one port and
transmitted to another port without moving between queues
• Allows for switching between different port speeds
© 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 27
Switch Speeds and Forwarding Methods
Duplex and Speed Settings
Two of the most basic settings on a switch are the bandwidth (“speed”) and duplex
settings for each individual switch port. It is critical that the duplex and bandwidth settings
match between the switch port and the connected devices.
There are two types of duplex settings used for communications on an Ethernet network:
• Full-duplex - Both ends of the connection can send and receive simultaneously.
• Half-duplex - Only one end of the connection can send at a time.
Autonegotiation is an optional function found on most Ethernet switches and NICs. It
enables two devices to automatically negotiate the best speed and duplex capabilities.
Note: Gigabit Ethernet ports only operate in full-duplex.
© 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 28
Switch Speeds and Forwarding Methods
Auto-MDIX
Connections between devices once required the use of either a crossover or straight-
through cable. The type of cable required depended on the type of interconnecting
devices.
Note: A direct connection between a router and a host requires a cross-over connection.
• Most switch devices now support the automatic medium-dependent interface
crossover (auto-MDIX) feature. When enabled, the switch automatically detects the
type of cable attached to the port and configures the interfaces accordingly.
• The auto-MDIX feature is enabled by default on switches running Cisco IOS Release
12.2(18)SE or later. However, the feature could be disabled. For this reason, you
should always use the correct cable type and not rely on the auto-MDIX feature.
• Auto-MDIX can be re-enabled using the mdix auto interface configuration command.
© 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 29
7.5 Module Practice and Quiz
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Module Practice and Quiz
What did I learn in this module?
• Ethernet operates in the data link layer and the physical layer. Ethernet standards define both
the Layer 2 protocols and the Layer 1 technologies.
• Ethernet uses the LLC and MAC sublayers of the data link layer to operate.
• The Ethernet frame fields are: preamble and start frame delimiter, destination MAC address,
source MAC address, EtherType, data, and FCS.
• MAC addressing provides a method for device identification at the data link layer of the OSI
model.
• An Ethernet MAC address is a 48-bit address expressed using 12 hexadecimal digits, or 6
bytes.
• When a device is forwarding a message to an Ethernet network, the Ethernet header
includes the source and destination MAC addresses. In Ethernet, different MAC addresses
are used for Layer 2 unicast, broadcast, and multicast communications.
© 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 31
Module Practice and Quiz
What did I learn in this module? (Contd.)
• A Layer 2 Ethernet switch makes its forwarding decisions based solely on the Layer 2
Ethernet MAC addresses.
• The switch dynamically builds the MAC address table by examining the source MAC address
of the frames received on a port.
• The switch forwards frames by searching for a match between the destination MAC address
in the frame and an entry in the MAC address table.
• Switches use one of the following forwarding methods for switching data between network
ports: store-and-forward switching or cut-through switching. Two variants of cut-through
switching are fast-forward and fragment-free.
• Two methods of memory buffering are port-based memory and shared memory.
• There are two types of duplex settings used for communications on an Ethernet network: full-
duplex and half-duplex.
© 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 32
Module 7: Ethernet Switching
New Terms and Commands
• Store-and-Forward Switching
• Cut-through Switching
• Fast-Forward Switching
• Fragment-free Switching
• OUI (Organizationally Unique Identifier)
• ARP (Address Resolution Protocol)
• ND (Neighbor Discovery)
• Port-based memory
• Shared memory
• Auto-MDIX
© 2016 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 33
INFO-1280
Assigned Reading
BEFORE next class please read:
No Reading – Study for Test #1
From your Account on the Cisco Networking Academy Website.
(You do not have to purchase the book it is free on-line using your account)
34
Michael McNorgan 2020
INFO-1280
Theory Assessments:
Theory Component (on campus)
Test #1
Monday Feb. 10th 9-11am (10%)
Test #2
Monday March 31st 9-11am (20%)
Final Exam – Exam week (20%)
• Refer to college exam schedule when available
Tests/exams are on campus, not online
Room booking will be posted when available 35
Michael McNorgan 2020
INFO-1280
Practical Assessments:
Practical (in-class lab assignments) Component
Lab Assignment #1 (5%)
• Week of January 27th
Lab Assignment #2 (10%)
• Week of February 24th
Lab Assignment #3 (15%)
• Week of March 24th
Lab Assignment #4 (20%)
• Friday April 11th
• Monday April 14th
• Wednesday April 16th
The actual day/time is your regular lab day/time for that week.
This is not a take home assignment; it is completed in lab on the equipment. 36
Michael McNorgan 2020
