Cisco® CCNA ICND2 Exam Cram Notes : Switch IOS


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1. LAN Switching Technologies

1.1 Switch IOS

The following commands are used for configuring the switch ports.

Set the port speed to 100 mbps, and inter-switch communication to full-duplex on Switch 2950 of ports fa 0/2

2950#configure terminal
fastethernet 0/2

To enable a switch port for layer 2 functionality use the following commands:

1. switch(config)#interface <type> <mod>/<num>

2. switch(config-if)#switchport

The first command enters interface configuration mode for the switch interface < mod >/<num >, and the second command enables layer 2 functionality on the port.

Use the "no" form of the switchport command to enable layer3 functionality.

The following commands are used for configuring the switch ports ip address and enabling the interface

SW1#configure terminal
fastethernet 0/1
SW1(config-if)#ip address
SW1(config-if)#no shutdown

Connect to SW1 and configure fast ethernet interface fa 0/11 on the switch and Configure trunking on the switch by issuing command switchport mode trunk

SW1#configure terminal
fastethernet 0/11
SW1(config-if)#switchport mode trunk

Packet-switched networks can efficiently use multiple routes inside a service provider network because the routes are formed dynamically.

The command:

Switch(config)# port-channel load-balance src-ip

Will configure load balancing on EtherChannel switch links using source IP address.

Note that the load balancing can be done based on source IP, destination IP, both source and destination IP (XOR), source and destination MAC addresses or TCP/UDP port numbers

The command:

Switch#show etherchannel summary

Shows each port in the channel along with the status flag.

To find out which interface associated with a given MAC address, use the "show mac-address-table" command. It shows the learned MAC addresses and their associated interfaces.

If no matching MAC entry is found in the MAC table of a switch, the frame will be broadcast to all other ports except the port through which it had arrived.

Use the "show interface trunk" command to determine the trunking status of a link and VLAN status. This command lists port, its mode, encapsulation and whether it is trunking enabled.

The command "ip default-gateway <defaultgatewayadd>" in global configuration mode can be used to set the default gateway on a Cisco switch/router.

Switches forward packets based on the physical address (such as MAC address) whereas, routers forward packets based on logical address (such as IP address). A frame's MAC address doesn't change when being forwarded through a switch.

The MAC address table of a switch would be empty to begin with. However, it builds the MAC table learning from the frames that arrive at its ports by adding the MAC address and the corresponding port that it had arrived to the MAC table. In this case, there is no MAC entry for interface Fa0/10. Therefore, a new entry will be added to the MAC table with the MAC (of00a0.2a38.f23a) address of HostC

You can use "show controllers serial [port number]" to see if the interface detects a DCE or DTE cable.

The following are the Cisco recommended Access Layer switches:

  • Catalyst 2950: For less than 50 users 10/100BaseT; 100BaseFX or 1000Base-X uplinks
  • Catalyst 3550: For less than 50 users 10/100BaseT; 1000Base-X uplinks;Advanced QOS, Inline power
  • Catalyst 4000/4500: For 250+ users 10/100/1000Base-T; 1000Base-X uplinks; Advanced QOS, Inline power.

Note that Catalyst 4000/4500 Supervisor III and IV support Cisco IOS.

An interface can be manually shut down by the administrator by issuing "shutdown" command. In such case, the command "show interfaces" displays the status as 'administratively down'.

The command "no switchport" enables a switch port for layer 3 operation. On the other hand, the command "switchport" enables a switch port for layer 2 operation.

Debug commands are useful to observe the switch responses in real time. To disable a debug command use "no debug" command. Using "no debug all" or "undebug all" command can disable all currently running debug commands.

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