Cabling, Devices, & Switching
Eric A. Greve 2014
Internetworking Technology
Foy H. Moody High School
Ethernet = 802.3
Switching=Layer 2 (Data Link)
“Ethernet Switching”
Physical Devices Implementing Ethernet
Collision Free
Cisco
Routers
&
Switches
 Switches provide segmentation of a LAN, dividing the LAN into
independent collision domains.
 Each port on a switch represents a separate collision domain
and provides the full media bandwidth to the node or nodes
connected on that port.
What is Auto-MDIX ?
 Auto-MDIX on an Interface
 When automatic medium-dependent interface crossover (autoMDIX) is enabled on an interface, the interface automatically detects
the required cable connection type (straight through or crossover)
and configures the connection appropriately. When connecting
switches without the auto-MDIX feature, you must use straightthrough cables to connect to devices such as servers, workstations,
or routers and crossover cables to connect to other switches or
repeaters. With auto-MDIX enabled, you can use either type of cable
to connect to other devices, and the interface automatically corrects
for any incorrect cabling. For more information about cabling
requirements, see the hardware installation guide.
Auto-MDIX
Crossover
Straight-through
Straight-through
Crossover
 Connections between specific devices, such as switch-to-switch,
switch-to-router, switch-to-host, and router-to-host device, once
required the use of a specific cable types (crossover or straightthrough).
 Modern Cisco switches support the mdix auto interface
configuration command to enable the automatic medium-dependent
interface crossover (auto-MDIX) feature.
Dedicated Bandwidth
Full Duplex Operation
 A Cisco Catalyst switch supports three duplex settings:
 The full option sets full-duplex mode.
 The half option sets half-duplex mode.
 The auto option sets autonegotiation of duplex mode which
enables two ports to decide the best mode of operation.
 For Fast Ethernet and 10/100/1000 ports, the default is auto.
 For 100BASE-FX ports, the default is full.
 The 10/100/1000 ports operate in either half- or full-duplex mode
when they are set to 10 or 100 Mb/s, but when set to 1,000 Mb/s,
they operate only in full-duplex mode.
What is duplexing in Telecommunications
 A duplex communication system is a point-to-point system
composed of two connected parties or devices that can
communicate with one another in both directions. There are two
types of duplex communication systems: full-duplex and half-duplex.
 In a full duplex system, both parties can communicate to the other
simultaneously. An example of a full-duplex device is a telephone;
the parties at both ends of a call can speak and be heard by the
other party simultaneously.
 In a half-duplex system, in contrast, each party can communicate to
the other, but not simultaneously; the communication is one
direction at a time. An example of a half-duplex device is a walkietalkie two-way radio that has a "push-to-talk" button; when the local
user wants to speak to the remote person they push this button,
which turns on the transmitter but turns off the receiver, so they
cannot hear the remote person.
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Collision Free
Ethernet Switching
 When only one host is connected to a
switch port, the collision domain on the
shared media contains only two nodes:
 The switch port
 The host connected to it.
 These small physical segments are
called microsegments or
 “Microsegmentation”.
Switches
 Switches separate collision domains.
 They do not separate broadcast domains.
 Only routers separate broadcast domains.
Switch Builds Its MAC Table
F0/1
F0/8
F0/2
F0/7
F0/3
F0/4
F0/5
F0/6
Basic Switch Operations
 All switches perform the following tasks:
Learning
• Source MAC addresses are mapped to the ports to which they are connected.
Aging
• All learned entries are time stamped and kept in the CAM table for 300 sec. (5
minutes) before they age out.
• The entry is refreshed every time the source hosts sends a frame.
Selective
Forwarding
• Switches make forwarding decisions using either store-and-forward switching or
cut-through switching.
Flooding
• If a switch has no entry in its MAC address table for the destination MAC, its
default action is to send the frame out every port (except the one it came in on).
Filtering
• This is when a switch:
• Does not forward a frame to the same port on which it arrived.
• Drops a corrupt frame.
• Security settings are blocking the MAC addresses and port binding.
Selective Forwarding
Cut-Through
Cut-Through
Store-and-Forward
Lowest Latency
Fragment Free
Highest Latency
No error checking
Low Latency
All errors filtered
Checks for collisions
(Filters most errors)
Lowest Latency
Less Error Checking
Highest Latency
More Error Checking
Symmetric and Asymmetric Switching
Symmetric Switching
• All ports operate at same bandwidth.
• Supported by store-and-forward and cutthrough switching.
Asymmetric Switching
• Ports can be of differing bandwidths.
• Requires store-and-forward switching and
shared memory buffering.
• Most switches are now asymmetric to allow
flexibility.
Enterprise Level
Switches
Cisco Switches
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Switch Form Factors
Fixed Configuration Switches
•
•
•
•
•
Modular Configuration Switches
•
•
•
•
Features and options are limited to those that
originally come with the switch.
The number of ports cannot be increased.
Switch may be stackable.
Layer 2 switch: Catalyst 2960
Layer 3 switch: Catalyst 3650
Large enterprise class switches.
The chassis is totally customizable as
different line cards can be used.
Adding additional line cards increases port
density.
Catalyst 4500, 6500, 6800
Stackable Configuration Switches
•
•
Stackable switches, interconnected by a
special cable and makes the combined group
of switches operate as one large switch.
Catalyst 3750
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Enterprise Level Switches
 Characteristics of enterprise level switches include:
 Port Density: This is the number of ports available on a single
switch.
 High Forwarding Rates: Defines the processing capabilities of
a switch by rating how much data the switch can process per
second.
 Support for Link Aggregation: Helps reduce traffic bottlenecks
by allowing up to 8 switch ports to be bound and provide higher
throughput.
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Power over Ethernet (PoE)
 Allows the switch to deliver power to a device over the existing
Ethernet cabling.
 Can provide power to IP phones and wireless access points.
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Layer 2 versus
Layer 3 Switches
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Layer 2 Functions
 Typically, switches operate at OSI Layer 2
 It makes forwarding decisions based on the MAC addresses of
devices connected to switch ports.
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Layer 2 verses Layer 3 Switching
 Layer 3 switches (also known as multilayer switches) offer advanced
functionality.
 It makes forwarding decisions based on MAC and/or IP
addresses of devices connected to switch ports.
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