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10/100/1000 ports.
Auto-negotiation can produce unpredi ctable results.
If auto-negotiation fails because the attached device does not support it, t he Catalyst switch defaults the switch
port to half-duplex mode.
Half-duplex on one end and full-duplex on the other causes late collision errors at the half-duplex end.
To avoid this, manually set the duplex parameters o f the switch to match the attached device.
Auto-MDIX feature:
In the past, either a cross-over or a straight-thro ugh cable was required depending on the type of dev ice that was
being connected to the switch.
Instead, the mdix auto interface configuration comm and enables the automatic medium-dependent interfac e
crossover (auto-MDIX) feature.
With this feature enabled, the switch detects the i nterface required for copper media and configures t he interface
accordingly.
FULL:
Full-duplex mode.
Default for 100BASE-FX ports.

HALF:
Half-duplex mode.
Switch MAC Address Table
Switches use MAC addresses to direct network traffi c to the appropriate port.
A switch builds a MAC address table by learning the MAC addresses of each device connected to each of its ports.
Once the MAC address has been added to the table, t he switch uses the table entry to forward traffic to that node.
If a destination address is not in the table, the s witch forwards the frame out all ports except the r eceiving port.
When the destination responds, the MAC address is a dded to the table.
If the port is connected to another switch or a hub , multiple MAC addresses will be recorded in the ta ble.

Example Step 1:
The switch receives a broadcast frame from PC 1 on Port 1.

Example Step 2:
The switch enters the source MAC address and the switch port that received the frame into the address table.
Example Step 3:
Because the destination address is a broadcast, the switch floods the frame to all ports , except the port on which
it received the frame.
Example Step 4:
The destination device replies to the broadcast wit h a unicast frame addressed to PC1 .
Example Step 5:
The switch enters the source MAC address(destinatio n add. Of the frame & its associated port is found in the MAC
add. table) of PC 2 and the port number of the swit ch port that received the frame into the address table.
Example Step 6:
The switch can now forward frames between source an d destination devices because it has entries in the address
table that identify the associated ports.
Design Considerations – Ethernet/802.3
Bandwidth and Throughput:
A major disadvantage of Ethernet is collisions.
When two hosts transmit frames simultaneously, the collision results in the transmitted frames being corrupted or
destroyed.
The sending hosts stop sending based on the Etherne t 802.3 rules of CSMA/CD.
-It is important to understand that when stating the bandwidth of the Ethernet network is 10 Mb/s, ful l bandwidth for
transmission is available only after any collisions have been resolved .

A hub offers no mechanisms to either eliminate or reduce collisions and the a vailable bandwidth that any one
node has to transmit is correspondingly reduced.
As a result, the number of nodes sharing the Ethernet network will have effect on the throughput.
Collision Domains:

To reduce the number of nodes on a given network segment, you can create separate physical network segments
called collision domains.
The network area where frames originate and collide is called the collision domain.
All shared media environments, such as those created by using hubs are collision domains.
When a host is connected to a switch port, the switch creates a dedicated connection. This connection is an
individual collision domain.
Microsegment:
When two connected hosts want to communicate with e ach other, the switch uses the switching table to establish a
connection between the ports.
The circuit is maintained until the session is term inated.
The microsegment behaves as if the network has only two hosts, providing maximum available bandwidth to both
hosts.
Switches reduce collisions and improve bandwidth use on network segments because they provide dedicated
bandwidth to each network segment .

Broadcast Domains:
Although switches filter most frames based on MAC a ddresses, they do not filter broadcast frames .
Why?
Because a