CN2668
Routers and Switches (V2)
Kemtis Kunanuraksapong
MSIS with Distinction
MCTS, MCDST, MCP, A+
Agenda
• Chapter 12: Basic Switching and Switch
Configuration
• Exercise
• Quiz
Ethernet Operations
• Carrier Sense Multiple Access with Collision
Detection (CSMA/CD)
▫ Ethernet contention method
▫ Any station connected to a network can transmit
anytime a transmission is not present on the wire
• Interframe gap or interpacket gap (IPG)
▫ Each station must wait a minimum of 9.6
microseconds before transmitting another packet
Ethernet Operations (Cont.)
• Collisions
• Collision Domain
• Broadcasts
▫ Increase the speed/performance by disable the
unnecessary service such as IPX where it is not
needed
Latency or propagation delay
• The length of time that is required to forward,
send, or otherwise propagate a data frame
• Latency depends on
▫ the resistance offered by the transmission
medium, the number of nodes
▫ The amount of processing that must be done on
the packet
• Transmission time
▫ The amount of time it takes for a packet to be sent
from one device to another
Latency (Cont.)
• Bit time
▫ The amount of time required to transmit one bit
• Slot time (512 bit times)
▫ A specification that limits the physical size of each
Ethernet collision domain
 All collisions should be detected from anywhere in a
network in less time than is required to place a 64byte frame on the network
 5-4-3 rule
 Five segments of wire, four repeaters, 3 populated hubs
between any two stations on 10-Mbps network
Ethernet Errors
• Frame size errors
▫ Short frame or runt
 a frame shorter than 64 bytes
▫ Long frame or giant
 a frame greater than 1518 bytes
▫ Jabber
 a frame longer than 1518 bytes and has wrong FCS
• Frame check sequence (FCS) error
▫ Indicates that bits of a frame were corrupted
during transmission
Ethernet Errors
• Collision errors
▫ Reducing the number of devices per collision
domain will usually solve the problem
• Late collision
▫ Occurs when two stations transmit more than 64
bytes of data frames before detecting a collision
Fast Ethernet (100 Mbps)
• Uses the same CSMA/CD as 10BaseT Ethernet
• Defined under the IEEE 802.3u standard
• Implementations
▫
▫
▫
▫
100Base-TX
100Base-T4
100Base-FX
See Page 342 for detail implementation
Gigabit Ethernet (1000 Mbps)
• Gigabit Ethernet implementations
▫
▫
▫
▫
1000Base-TX (802.3ab)
1000Base-SX (802.3z)
1000Base-LX (802.3z)
1000Base-CX (802.3z)
Half- and Full-Duplex Communications
• Half-duplex communications
▫ Devices can send and receive signals, but not at
the same time
• Full-duplex (or duplex) communications
▫ Devices can send and receive signals
simultaneously
• Ethernet networks can use equipment that
supports half- and full-duplex communications
Half- and Full-Duplex Communications
• On a Cisco Catalyst 2950 switch, you can set the
duplex capabilities port-by-port
• The four different duplex options are:
▫ Auto
▫ Full
▫ Full-flow control
 Use for 100Base-TX ports only
▫ Half
A Review of LAN Segmentation
• Improve the performance of Ethernet network
▫ By reducing the number of stations per collision
domain
▫ Implement bridges, switches, or routers to
segment the network and divide the collision
domains
Segmenting with Bridges
• Segments a network by filtering traffic at the
Data Link layer
• Divides a network into two or more segments
 Only forwards a frame from one segment to another
if the frame is a broadcast or has the MAC address of
a station on a different segment
• Bridges learn MAC addresses by reading the
source MAC addresses from frames
▫ As the frames are passed across the bridge
Segmenting with Bridges (continued)
• Bridging table
▫ Maps the MAC addresses on each segment to the
corresponding port on the bridge to which each
segment is connected
• Bridges increase latency, but because they
effectively divide the collision domain
▫ This does not affect slot time
Segmenting with Routers
• Operates at layer 3 of the OSI reference model
• Interprets the Network layer protocol and makes
forwarding decisions based on the layer 3
address
• Routers typically do not propagate broadcast
traffic
• Routers maintain routing tables that include the
Network layer addresses of different segments
Segmenting with Routers (continued)
•
•
•
•
•
Decrease collisions by filtering traffic
Reduce broadcast and multicast traffic
Support multiple paths and routes between them
Provide increased
Provide layer 3 routing, packet fragmentation
and reassembly, and traffic flow control
• Provide communications between different
technologies
LAN Switching
• Switches are often called multiport bridges
▫ Segmenting a LAN into multiple collision domains
• Switches microsegment the network
▫ By connecting each port to an individual
workstation
• Switched bandwidth
▫ Bandwidth is not shared as long as each
workstation connects to its own switch port
19
CCNA Guide to
Cisco
Networking
Fundamentals,
Fourth Edition
Switch Operations
• A switch learns the hardware address of devices to
which it is attached
▫ By reading the source address of frames
• The switch then matches the source MAC address
with the port from which the frame was sent
▫ The MAC-to-switch-port mapping is stored in the
switch’s content-addressable memory (CAM)
• The switch uses a memory buffer to store frames as
it determines to which port(s) a frame will be
forwarded
Switch Operations
• Types of memory buffering:
▫ Port-based memory buffering
 Each port has its own buffer memory
▫ Shared memory buffering
• Asymmetric switching
▫ Can interconnect network interfaces of different
speeds
• Symmetric switching
▫ Require all attached network interface devices to
use the same transmit/receive speed
Switching Methods
• All switches base frame-forwarding decisions on
a frame’s destination MAC address
• The three main methods for processing and
forwarding frames are:
▫
▫
▫
▫
Cut-through
Store-and-forward
Fragment-free
Adaptive cut-through forwarding
 A combination of the cut-through and store-andforward methods
Cut-Through Forwarding
• Send a frame immediately after reading the
destination MAC address into their buffers
• The main benefit is a reduction in latency
• The drawback is the potential for errors in the
frame that the switch would be unable to detect
▫ Because the switch only reads a small portion of
the frame into its buffer
• See Figure 12-5 on Page 249 for the amount of
bit read
Store-and-Forward Forwarding
• Read the entire frame, no matter how large, into
their buffers before forwarding
▫ It will not forward frames with errors
• The store-and-forward method has the highest
latency
• See Figure 12-6 on Page 350
Fragment-Free Forwarding
• Reads the first 64 bytes of an Ethernet frame
▫ Then begins forwarding it to the appropriate
port(s)
▫ An effort to provide more error-reducing benefits
than cut-through switching
▫ Latency lower than store-and-forward switching
▫ See Figure 12-7 on Page 350
Adaptive cut-through Forwarding
• For the most part, the adaptive cut-through
switch will act as a cut-through switch
• If a certain level of errors is detected, the switch
will
▫ Change forwarding techniques to act more as a
store-and-forward switch
Switch User Interface
• Two types of operating systems are in use on
Cisco switches
▫ IOS-based
 Catalyst 1900, 2820, 2900
▫ Set-based
 Older and uses set commands
 1984G, 2926, 4000, 5000, and 6000 series
▫ The Cisco switch has a console port to which you
can connect your laptop or PC
• Once you power on the switch you will be in the
command-line interface
Modes and Passwords
• You CANNOT actually configure a switch until
you get to enable mode
• To enter enable mode
▫ Type enable at the command-line prompt
• The first step in configuring a switch is to set up
a password
▫ To start configuration mode
 Type configure terminal or config t at the
command prompt
Modes and Passwords (Cont.)
• A secret (encrypted) password
▫ Switch(config)# enable secret ccnasafe
▫ Cannot be retrieved from the configuration file
• Password on VTY (telnet) or console line
▫ Switch(config)# service password-encryption
▫ Switch(config)# line vty 0 15
▫
▫
▫
▫
▫
▫
 For telnet, from line 0 to 15
Switch(config-line)# password vtysafe
Switch(config-line)# Exit
Switch(config)# line con 0
Switch(config-line)# password consolesafe
Switch(config-line)# Exit
Switch(config)# copy run start
 To save your configuration to the startup config
Setting the Host Name
• To configure this name, you would type:
▫ Switch(config)#hostname name
• Once the host name is set, the prompt will
change to reflect the name of the switch
IP on the Switch
• By default, Cisco switches are not configured
with IP addresses
▫ Configure an IP address for your switch so that
you can manage it over the network
▫ If you want to implement VLANs on your network
 Switch(config)# int vlan 1
 Switch(config-if)# ip address 192.168.1.204
255.255.255.0
 Switch(config-if)# exit
 Switch(config)# ip default-gateway 192.168.1.1
 Switch(config)# ip domain-name classroom
Configuring Switch Ports
• To enter interface configuration mode for the
first port of a switch named Rm410HL, you
would use the following commands:
▫ Rm410HL#configure terminal
▫ Rm410HL(config)#interface f0/1
▫ Rm410HL(config-if)#
• To view the configuration of a port, use the show
command
Configuring Switch Ports (continued)
• Configuring the duplex mode
▫ Rm410HL#configure terminal
▫ Rm410HL(config)#interface f0/24
▫ Rm410HL(config-if)#duplex full
Securing Switch Ports
• Several option of security on a switch
▫ Configure a permanent MAC address for a specific
port on your switch
▫ Define a static MAC address entry into your
switching table
 Maps a restricted communication path between two
ports
▫ Configure port security
 Setting a limit on the number of MAC addresses
Securing Switch Ports (continued)
• Display options by typing the following command:
▫ Rm410HL(config-if)#switchport portsecurity ?




Aging
Mac-address
Maximum
Violation
▫ Rm410HL(config-if)#switchport mode
access
▫ Rm410HL(config-if)#switchport portsecurity
Securing Switch Ports (continued)
• Aging
• Mac-address
▫ Tie a specific MAC address to a specific port
 Rm410HL(config-if)#switchport port-security Macaddress 0000.aaaa.bbbb
• Maximum
▫ Default value is 1; Range is 1 – 132 per interface
 Rm410HL(config-if)#switchport port-security
Maximum 10
Securing Switch Ports (continued)
• Violation
▫ What happens when a switch encounters a
violation of the configured switchport security
▫ Protect
 Stop forwarding the traffic of the exceeded MAC
address (11th and above; if it was set maximum to 10)
▫ Restrict
 Same as protect. Also sends an alert
▫ Shutdown
 By default to shut the interface down
Securing Switch Ports (continued)
• To turn switchport security off, use:
▫ Rm410HL(config-if)#no switchport
port-security
• To clear the settings to include erasing the static
MAC addresses, use the clear command:
▫ Rm410HL(config-if)#clear portsecurity
Assignment
• Review Questions
▫ 1 – 25
• Lab 12.1