chapter 10 - switchingccnapresentation.ppt

© 2007 Cisco Systems, Inc. All rights reserved. ICND1 v1.0—2-1
Benefits of
Switching

Switches

Layer 2 Switching
Purposes for using switching
 Breaks up collision domains
 Cost-effective, resilient internetwork
Purpose for Spanning-Tree Protocol (STP)
 Stops loops in layer 2 switched networks

Microsegmentation
Microsegmentation of the Network

Switching Services
Layer 2 switching provides:
 Hardware-based bridging
 Wire speed
 Low latency
 Low cost
Limitations of Layer 2 Switching
Must break up the collision domains correctly.
Switches do not break up broadcast domains by default.

Switch Functions at Layer-2
1. Address Learning
Layer 2 devices remember the source hardware address of each
frame received on an interface and they enter this information
into MAC database called forward/filter table.
2. Forward/Filter decisions
When a frame is received on an interface, the switch looks at the
destination hardware address and finds the exit interface in the
MAC database. The frame is only forwarded out the specified destination
port.
3. Loop avoidance
If multiple connections between switches are created redundancy,
network loops can occur. Spanning Tree Protocol (STP) is used
to stop network loops.

Blocking
As a switch powers on, each port cycles through a
series of four states:

Listening

Learning

Forwarding

Switching Frames:
How Switches Learn Hosts’ Locations
A switch builds a MAC address table by learning the MAC
addresses of the hosts that are connected to each switch port
Because the destination address is a broadcast, the switch floods
the frame to all ports, except the port on which it received the
frame.

Switching Frames:
(cont)
The destination device replies to the broadcast with
a unicast frame addressed to PC 1.

Switching Frames:
(cont)
The switch can now forward frames between source
and destination devices without flooding, because it
has entries in the address table that identify the
associated ports.

Half Duplex (CSMA/CD)
 Unidirectional data flow
 Higher potential for collision
 Hub connectivity
Full Duplex
 Point-to-point only
 Attached to dedicated switched port
 Requires full-duplex support on both ends
 Collision-free
 Collision detect circuit disabled
Duplex Overview

Cisco Catalyst 2960 Series
SwitchX(config)#interface fa0/1
SwitchX(config-if)#duplex {auto | full | half}
Cisco Catalyst 2960 Series
SwitchX(config)#interface fa0/1
SwitchX(config-if)#speed {10 | 100 | 1000 | auto}
Setting Duplex and Speed Options

SwitchX#show interfaces fastethernet0/2
FastEthernet0/2 is up, line protocol is up (connected)
Hardware is Fast Ethernet, address is 0008.a445.9b42 (bia 0008.a445.9b42)
MTU 1500 bytes, BW 10000 Kbit, DLY 1000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Keepalive set (10 sec)
Half-duplex, 10Mb/s
input flow-control is unsupported output flow-control is unsupported
ARP type: ARPA, ARP Timeout 04:00:00
Last input 00:00:57, output 00:00:01, output hang never
Last clearing of "show interface" counters never
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: fifo
Output queue: 0/40 (size/max)
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
323479 packets input, 44931071 bytes, 0 no buffer
Received 98960 broadcasts (0 multicast)
1 runts, 0 giants, 0 throttles
1 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
0 watchdog, 36374 multicast, 0 pause input
0 input packets with dribble condition detected
1284934 packets output, 103121707 bytes, 0 underruns
0 output errors, 2 collisions, 6 interface resets
0 babbles, 0 late collision, 29 deferred
0 lost carrier, 0 no carrier, 0 PAUSE output
0 output buffer failures, 0 output buffers swapped out
Showing Duplex Options

Core Layer
The typical hierarchical design model is broken up in
to three layers: access, distribution, and core. The
core layer of the hierarchical design is the high-speed
backbone of the internetwork.

Distribution Layer
Distribution layer controls the flow of network traffic using
policies and delineates broadcast domains by performing
routing functions between virtual LANs (VLANs) defined at
the access layer.

Access Layer
The main purpose of the access layer is to provide a
means of connecting devices to the network and
controlling which devices are allowed to communicate
on the network.

A Hierarchical Network in a Medium
Business

chapter 10 - switchingccnapresentation.ppt

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