CCNP_sdbsdbsdbsdbsdbsdbsdbsdbsdbsdbS1.pdf

This chapter covers the following basic switching topics as a
review to CCNA and serves as a teaser for topics covered later in
chapter:
•Hubs and switches
•Bridges and switches
•Switches of today
•Broadcast domains
•MAC addresses
•The basic Ethernet frame format
•Basic switching function
•VLANs
•The Spanning Tree Protocol
•Trunking
•Port channels
•Multilayer switching (MLS)

🔹 What is a Hub?
A hub is a basic networking device that connects multiple
computers or devices in a Local Area Network (LAN). It operates
at Layer 1 (Physical Layer) of the OSI model, meaning it does not
process data—it just forwards it.
🔹 How Does a Hub Work?
•When a device sends data to a hub, the hub broadcasts the data
to all connected devices.
•The intended recipient picks up the data, while the rest ignore
it.
•Hubs do not learn MAC addresses or filter traffic.
🔹 Types of Hubs
1.Passive Hub – Just forwards data without amplifying it.
2.Active Hub – Regenerates and amplifies signals before sending
them.
3.Intelligent Hub – Includes basic management features like
monitoring traffic.

🔹 Advantages of a Hub
✅ Simple & Cheap – Very easy to set up and cost-effective.
✅ Plug and Play – No configuration required.
✅ Good for Small Networks – Works for simple LANs with a
few devices.
🔹 Disadvantages of a Hub
❌ Broadcasts Data to All Devices – Causes network
congestion and security risks.
❌ Creates a Single Collision Domain – Collisions occur when
multiple devices send data simultaneously.
❌ No Traffic Filtering – No ability to optimize or manage
network performance.
❌ Limited Speed – Slower than modern network devices.

Hubs
•Legacy
•Layer 1 devices
•Multi-port repeaters
•Shared bandwidth
•Based on legacy bus topology
•CSMA/CD
•Single collision domain

🔹 What is a Bridge?
A bridge is a networking device that connects two separate LAN segments
and forwards traffic between them intelligently. It operates at Layer 2 (Data
Link Layer) of the OSI model and learns MAC addresses to filter and forward
traffic efficiently.
🔹 How Does a Bridge Work?
•Bridges store and analyze MAC addresses of devices in each LAN segment.
•When data is sent, the bridge checks its MAC table:
• If the destination is in the same segment, it blocks the data.
• If the destination is in a different segment, it forwards the data.
•This reduces unnecessary traffic and improves network efficiency.
🔹 Types of Bridges
1.Transparent Bridge – Most common, operates invisibly and filters traffic
based on MAC addresses.
2.Source Routing Bridge – Used in Token Ring networks, makes routing
decisions based on the sender's routing information.
3.Multiport Bridge – Connects multiple LAN segments and acts like a simple
switch.

🔹 Advantages of a Bridge
✅ Reduces Network Traffic – Filters traffic based on MAC addresses.
✅ Creates Separate Collision Domains – Improves performance.
✅ Enhances Security – Prevents unnecessary traffic from crossing
segments.
🔹 Disadvantages of a Bridge
❌ Slower Than Switches – Has to process and filter data before
forwarding.
❌ Limited Ports – Typically has only 2-4 ports (compared to switches
with 24-48 ports).
❌ Does Not Eliminate Broadcast Traffic – Broadcasts are still
forwarded.
🔹 When to Use a Bridge?
👉 To separate traffic between two LAN segments without using a
router.
👉 When you need basic filtering and traffic control but don’t need a
full switch.
👉 For legacy networks where upgrading to switches is not an option.

Switches
•Layer 2 devices
•Also operates at layer 1
•Full duplex
•Dedicated bandwidth

Switches Today
Application intelligence: This helps networks recognize many types of
applications and secure and prioritize those applications to provide
the best user experience.
Image Unified network services: Combining the best elements of
wireless and wired networking allows you to consistently connect to
any resource or person with any device. 10 Gigabit Ethernet
technology and Power over Ethernet (PoE) technology support new
applications and devices.
Image Nonstop communications: Features such as redundant
hardware, and nonstop forwarding and stateful switchover
(NSF/SSO) technology support more-reliable connections.
Image Integrated security: LAN switches provide the first line of
defense against internal network attacks and prevent unauthorized
intrusion.
Image Operational manageability: To more easily manage the network,
IT staff must be able to remotely configure and monitor network
devices from a central location.

Ethernet II and IEEE 802.3 standards define:
•Minimum frame size as 64 bytes
•Maximum as 1518 bytes
“collision fragment” or “runt frame” – Frame less than 64 bytes
If size of a transmitted frame is less than the minimum or greater than the maximum,
the receiving device drops the frame
In 1998, IEEE 802.3ac standard extended the maximum allowable frame size to 1522
bytes.
Increased to accommodate a technology called Virtual Local Area Network (VLAN).
VLANs will be presented in a later course.

5.2.1.4 – MAC Address Tables on Connected Switches
For every Ethernet frame that enters a port, the switch will:
Step 1: Learn (Building the MAC address table)
Switch learns by examining the source MAC address
•If not in MAC address table, then add it along with incoming
port number
•If in MAC address table, reset 5 minute timer
PC-A sends a frame to PC-B
The fame is received by switch S1

Switch S1 sees if it has something to learn by examining the source MAC address
The source MAC address is not in its MAC address table
S1 adds the source MAC address 00-0A and the incoming port 1 to its MAC
address table

Step 2: Forwarding the frame (Using the MAC address table)
Switch forwards by examining the destination MAC address
•If broadcast/multicast MAC address, flood out all ports except the
port it came in on
•If unicast MAC address is in MAC address table, send it out only
that port
•If unicast MAC address is not in in MAC address table, flood out
all ports except the port it came in on (unknown unicast)
S1 can now forward the frame by examining the destination MAC
address
The destination MAC address 00-0B is not in its MAC address
table, so it floods it out all ports
This is known as an unknown unicast

PC-B’s NIC receives the frame.
After comparing the destination MAC address of 00-0B to it own NIC’s
MAC address it realizes they are the same and copies in the rest of
the frame.

•If not in MAC address table, then add it along with incoming port
number
The frame is also flooded out S1’s port 4 which is connected to switch
S2
S2 receives the frame and examines the source MAC address
Since this is new information, S2 add the source MAC address 00-0A
and the incoming port number 1 to its MAC address table

•If broadcast/multicast MAC address, flood out all ports except
the port it came in on
that port
address
The destination MAC address 00-0B is not in its MAC address
Again, this is known as an unknown unicast

Both PC-C’s NIC and the Router’s NIC receives the frame.
Since their MAC addresses do not match the destination MAC
address they drop the rest of the frame

•If not in MAC address table, then add it along with incoming port number
PC-B now sends the frame to PC-A
The frame is received by switch S1

S1 adds the source MAC address 00-0B and the incoming port 3 to its MAC address
table

•If broadcast/multicast MAC address, flood out all ports except the port
it came in on
•If unicast MAC address is in MAC address table, send it out only that
port
•If unicast MAC address is not in in MAC address table, flood out all
ports except the port it came in on (unknown unicast)
address
The destination MAC address 00-0A is in its MAC address table, so it
filters the frame by sending it out only port 1

5.2.1.5 – Sending a Frame to the Default Gateway
Destination IP address is on a remote network.
PC-A will send the Ethernet frame to the MAC address of the default gateway
•If not in MAC address table, then add it along with incoming port number
Switch S1 sees if it has something to learn by examining the source MAC
address
The source MAC address is in its MAC address table, so it has nothing new to
learn
S1 refreshes the 5 minute refresh timer for this entry

•If broadcast/multicast MAC address, flood out all ports except
the port it came in on
that port
address
The destination MAC address 00-0D is not in its MAC address
This is known as an unknown unicast

PC-B’s NIC receives the frame and ignores the rest of the frame after
determining that the destination MAC address of 00-0D does not
match it’s own MAC address of 00-0B

If not in MAC address table, then add it along with incoming port number
If in MAC address table, reset 5 minute timer
The frame is also flooded out S1’s port 4 which is connected to switch S2
S2 receives the frame and examines the source MAC address
The source MAC address of 00-0A and port 1 is in its MAC address table,
so it has nothing new to learn

If broadcast/multicast MAC address, flood out all ports except the port it
came in on
If unicast MAC address is in MAC address table, send it out only that port
If unicast MAC address is not in in MAC address table, flood out all ports
except the port it came in on (unknown unicast)
S2 can now forward the frame by examining the destination MAC address
The destination MAC address 00-0D is not in its MAC address table, so it
floods it out all ports
Again, this is known as an unknown unicast

PC-C’s NIC and the Router’s NIC receives the frame.
PC-C’s MAC addresses does not match the destination
MAC address so it drops the rest of the frame
The router’s MAC address does match the destination
MAC address so it copies in the rest of the frame
The router will de-encapsulate the data from the
Ethernet frame and process the Layer 3 PDU, the IP
packet, for routing.

The router now sends the frame to PC-A
The frame is received by switch S2

S2 adds the source MAC address 00-0D and the incoming port 4 to its MAC address
table.

came in on
address

Switch S1 sees if it has something to learn by examining the source MAC
address.
The source MAC address is in its MAC address table, so it has nothing new
to learn.

came in on
S1 can now forward the frame by examining the destination MAC address

5.3.2.3 – ARP Operation – ARP Request
PCA at 192.168.1.110 has an IPv4 packet to send to 192.168.1.50
Comparing its IPv4 address with the destination IPv4 address, PCA
determines this device is on the same IP network

PCA checks its ARP table for 192.168.1.50 but no match

PCA puts the IPv4 packet on hold and
creates an ARP Request with
Target IPv4 = 192.168.1.50
Target MAC – unknown
Source MAC 00-A
Destination MAC = broadcast

PCA sends the ARP request which is received by the switch
Because the destination MAC is a broadcast the switch sends it out all ports but
the incoming port

PCB compares the target IPv4 address to its own MAC address and because
it is not a match ignores the ARP request

Router R1 compares the target IPv4 address to its own MAC address and because it
is not a match ignores the ARP request.
Routers do not forward broadcasts.

The target address in the ARP request matches PCC’s IPv4 address

5.3.2.4 – ARP Operation – ARP Reply
The target address in the ARP request matches PCC’s IPv4 address

PCC sends an ARP reply to the sender of
the ARP request
This is a unicast
Sender IPv4 = 192.168.1.50
Sender MAC – 00-0C
Source MAC 00-0C
Destination MAC = 00-0A

PCC Adds the sender’s IPv4 address and MAC address to its ARP table

PCC takes the IPv4 packet off hold
PCC uses the MAC address for the destination MAC address

PCA now sends this Ethernet frame with the encapsulated IPv4 packet
out its Ethernet NIC

5.3.2.5 – ARP Role in Remote Communication
PC A at 192.168.1.110 has an IPv4 packet to send to 10.1.1.10
Comparing its IPv4 address with the destination IPv4 address, PCA
determines this device is on a different IP network
PCA must sent this packet to its default gateway 192.168.1.1

PC A checks its ARP table for 192.168.1.1 but no match

PC A puts the IPv4 packet on hold and
creates an ARP Request with
Target IPv4 = 192.168.1.1
Target MAC – unknown
Source MAC 00-A
Destination MAC = broadcast

PC A sends the ARP request which is received by the switch
Because the destination MAC is a broadcast the switch sends it out all
ports but the incoming port

PC B compares the target IPv4 address to its own MAC address and because it is
not a match ignores the ARP request

PC C compares the target IPv4 address to its own MAC address and
because it is not a match ignores the ARP request

The target address in the ARP request matches the router’s the IPv4 address on
its G0/0 interface

PC C sends an ARP reply to the sender of
the ARP request
This is a unicast
Sender IPv4 = 192.168.1.1
Sender MAC – 00-0D
Source MAC 00-0D
Destination MAC = 00-0A

PC C Adds the sender’s IPv4 address and MAC address to its ARP table

PC C takes the IPv4 packet off hold
PC C uses the MAC address for the destination MAC address

PC A now sends this Ethernet frame with the encapsulated IPv4 packet out its
Ethernet NIC towards the default gateway

Understanding IPv4 communications

•Devices can only communicate with other devices on the same subnet
•Otherwise, they must go through a router, that is on its same subnet

Switch Type Description Features Use Cases
Unmanaged
Switch
Plug-and-play
switch with no
configuration
Simple, cost-
effective,
automatic MAC
address learning
Small home
networks, basic
office setups
Managed Switch
Allows full control
over traffic and
configurations
VLAN support,
QoS, SNMP
monitoring,
security features
Enterprise
networks, data
centers, large
businesses
Smart (Lightly
Managed) Switch
Limited
management
features via a web
interface
Basic VLAN, QoS,
limited monitoring
Small to medium-
sized businesses
needing some
control
1. Based on Management Capabilities

Layer 2 Switch
Operates at the
Data Link Layer
(L2), forwarding
packets based on
MAC addresses
VLAN support,
MAC filtering,
Spanning Tree
Protocol (STP)
LAN segmentation,
local traffic
handling
Layer 3 Switch
Functions like a
router, operating
at the Network
Layer (L3),
forwarding packets
based on IP
addresses
Routing between
VLANs, inter-VLAN
communication,
supports OSPF, RIP,
and static routes
Large LANs,
reducing router
dependency
2. Based on Layer Functionality

Enterprise Switch
Designed for large-
scale business
networks
High-speed,
redundancy,
multiple
management
protocols
Corporate
networks,
campuses
Data Center
Switch
High-performance
switches for
handling massive
traffic loads
High bandwidth,
low latency,
redundancy
Cloud services,
large-scale data
centers
Industrial Switch
Rugged design for
harsh
environments
High durability,
extreme
temperature
support
Manufacturing
plants, outdoor
networks
Campus Switch
Used for
educational
institutions and
large office
buildings
Scalable,
centralized
management
Universities, large
office campuses
3. Based on Deployment

Fixed Switch
Comes with a set
number of ports,
cannot be
expanded
Cost-effective,
suitable for small
setups
Small businesses,
home networks
Modular Switch
Expandable with
additional modules
High scalability,
customizable
Large enterprises,
data centers
Stackable Switch
Can be stacked
with multiple
switches to work
as one
Increased
redundancy,
simplified
management
Medium to large
networks needing
scalability
4. Based on Network Configuration

PoE (Power over
Ethernet) Switch
Provides power
along with data
over Ethernet
cables
Supports
PoE/PoE+ for
powering IP
cameras, VoIP
phones, and IoT
devices
Smart offices,
surveillance
systems
Fiber Switch
Uses fiber-optic
connections for
high-speed data
transfer
Supports SFP/SFP+
ports, low latency
Long-distance
networking, high-
speed backbones
KVM Switch
Controls multiple
computers using a
single keyboard,
video monitor,
and mouse
Multi-device
control
Data centers, IT
administrators
Ethernet Switch
Standard switch
for Ethernet
networks
Supports Fast
Ethernet, Gigabit
Ethernet, or
10GbE
General network
setups
5. Based on Connectivity & Technology

Gigabit Switch
Supports speeds
up to 1 Gbps per
port
Fast data transfer,
common in
modern networks
Homes, offices,
small data centers
10G/40G/100G
Switch
Supports high-
speed networking
for demanding
applications
Low latency, high
bandwidth
Data centers, cloud
computing, high-
performance
computing (HPC)
6. Based on Performance

Based on network architecture
Feature
Edge Switch
(Access Layer)
Distribution Switch
(Aggregation
Layer)
Core Switch
(Backbone Layer)
Main Function
Connects end
devices to the
network
Aggregates traffic
from edge switches
Provides high-
speed backbone
connectivity
Layer Layer 2 (mostly)
Layer 3 (Inter-VLAN
Routing)
Layer 3 (High-
speed Routing)
Speed 1G - 10G 10G - 40G 40G - 100G+
Redundancy Low
Medium (some
redundancy
features)
High (dual power,
failover support)
Traffic Type Local user traffic
Aggregated traffic
from edge switches
High-speed core
backbone traffic
Common Users
End-users, printers,
VoIP
Departments,
office buildings
Data centers,
corporate
backbones
Comparison Table

1. Define Your Network Requirements
A. Network Size & Scale
•Small Office/Home (1-20 users): Unmanaged or Smart switches
•Medium Business (20-200 users): Managed switch with VLAN support
•Large Enterprise (200+ users): Layer 3 switch with high-speed uplinks
•Data Center: Modular or core switch with redundancy
B. Performance Needs
•Low Traffic: 1Gbps ports are sufficient
•Medium Traffic: 10Gbps uplinks for smooth connectivity
•High Traffic (Data Center, Large Enterprise): 40G or 100G switches
C. Deployment Type
•Edge/Access Layer (End Devices): Layer 2, PoE support for VoIP/WiFi
•Distribution Layer (Aggregating Traffic): Layer 3, Inter-VLAN Routing
•Core Layer (Backbone Traffic): High-speed Layer 3 switch

Key Takeaways
•For home or small business → Unmanaged or Smart Switch
•For enterprises → Managed or Layer 3 Switch
•For high-speed networks → 10G/40G/100G or Fiber Switch
•For power-hungry devices → PoE Switch
•For data centers → Modular, Stackable, or Data Center Switch

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