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Tutorial: Cisco Catalyst 3560 Switch Interfaces Configuration

June 4 2012 , Written by Cisco & Cisco Router, Network Switch Published on #Cisco Switches - Cisco Firewall

It is important to understand how to access switch ports. The 3550 switch uses the type slot/port command, just like a 2621 router and just like the 3550 switch. For example, Fastethernet 0/3 is 10/100BaseT port 3.

The 3550 switch type slot/port command can be used with either the interface command or the show command. The interface command allows you to set interface specific configurations. The 3550 switch has only one slot: zero (0), just like the 1900.

Network Layout: Work with the saved network that you used to configure devices in lab 8.27.



Lab Steps

1. To configure an interface on a 3550 switch, go to global configuration mode and use the interface command as shown.

3550A#config t

Enter configuration commands, one per line.  End with CTRL/Z

3550A(config)#interface ?

   Async              Async interface

   BVI                Bridge-Group Virtual Interface

   Dialer             Dialer interface

   FastEthernet       FastEthernet IEEE 802.3

   Group-Async        Async Group interface

   Lex                Lex interface

   Loopback           Loopback interface

   Multilink          Multilink-group interface

   Null               Null interface

   Port-channel       Ethernet Channel of interfaces

   Transparent        Transparent interface

   Tunnel             Tunnel interface

   Virtual-Template   Virtual Template interface

   Virtual-TokenRing  Virtual TokenRing

   Vlan               Catalyst Vlans

   fcpa               Fiber Channel

   range              interface range command



2. The next output asks for the slot. Since the 3550 switch is not modular, there is only one slot, which is 0, although it lists 0-2 for some odd reason. However, you can only type in “0” as the slot in this program. Any other slot number will give you an error. The next output gives us a slash (/) to separate the slot/port configuration.

3550A(config)#interface fastethernet ?

  <0-2>  FastEthernet interface number

3550A(config)#interface fastethernet 0?


3550A(config)#interface fastethernet 0/?

  <0-12>  FastEthernet interface number


3. After the 0/configuration command, the above output shows the amount of ports you can configure. The output below shows the completed command.

3550A(config)#interface fastethernet 0/4



4. Once you are in interface configuration mode, the prompt changes to (config-if). After you are at the interface prompt, you can use the help commands to see the available commands.


Interface configuration commands:

      arp                 Set arp type (arpa, probe, snap) or timeout

      bandwidth           Set bandwidth informational parameter

      carrier-delay       Specify delay for interface transitions

      cdp                 CDP interface subcommands

      channel-group       Etherchannel/port bundling configuration

      default             Set a command to its defaults

      delay               Specify interface throughput delay

      description         Interface specific description

      dot1x               IEEE 802.1X subsystem

      duplex              Configure duplex operation.

      exit                Exit from interface configuration mode

      help                Description of the interactive help system

      hold-queue          Set hold queue depth

      ip                  Interface Internet Protocol config commands

      keepalive           Enable keepalive

      load-interval       Specify interval for load calculation for an interface

      logging             Configure logging for interface

      mac-address         Manually set interface MAC address

      mls                 mls interface commands

      mvr                 MVR per port configuration

      no                  Negate a command or set its defaults

      ntp                 Configure NTP


You can switch between interface configurations by using the int fa 0/# command at any time from global configuration mode.


5. Let’s look at the duplex and speed configurations for a switch port.


3550A(config)#int fa0/4

3550A(config-if)#duplex ?

  auto  Enable AUTO duplex configuration

  full  Force full duplex operation

  half  Force half-duplex operation


   10    Force 10 Mbps operation
100   Force 100 Mbps operation
auto  Enable AUTO speed configuration


6. Since the switch port’s duplex and speed settings are already set to auto by default, you do not need to change the switch port settings. It is recommended that you allow the switch port to auto negotiate speed and duplex settings in most situations. In a rare situation, when it is required to manually set the speed and duplex of a switch port, you can use the following configuration.

3550A(config-if)#speed 100

Duplex will not be set until speed is set to non-auto value

3550A(config-if)#duplex full

full duplex - transmission of data in two directions simultaneously. It has a higher throughput than half duplex.

There are no collision domains with this setting

Both sides must have the capability of being set to full duplex

Both sides of the connection must be configured with full duplex

Each side transmits and receives at full bandwidth in both directions


7. Notice in the above command that to run full duplex, you must set the speed to non-auto value.


8. In addition to the duplex and speed commands that can be configured on the switch port, you also can turn on what is called portfast. The portfast command allows a switch port to come up quickly. Typically a switch port waits 50 seconds for spanning-tree to go through its"gotta make sure there are no loops!" cycle. However, if you turn port fast on, then you better be sure you do not create a physical loop on the switch network. A spanning tree loop can severely hurt or bring your network down.    Here is how you would enable port fast on a switch port.

3550A(config-if)#spanning-tree ?

  bpdufilter     Don't send or receive BPDUs on this interface

  bpduguard      Don't accept BPDUs on this interface

  cost           Change an interface's spanning tree port path cost

  guard          Change an interface's spanning tree guard mode

  link-type      Specify a link type for spanning tree protocol use

  port-priority  Change an interface's spanning tree port priority

  portfast       Enable an interface to move directly to forwarding on link up

  stack-port     Enable stack port

  vlan           VLAN Switch Spanning Tree


9. The command above shows the available options for the spanning-tree command. We want to use the portfast command.

3550A(config-if)#spanning-tree portfast

%Warning: portfast should only be enabled on ports connected to a single

 host. Connecting hubs, concentrators, switches, bridges, etc... to this

 interface  when portfast is enabled, can cause temporary bridging loops.

 Use with CAUTION

%Portfast has been configured on FastEthernet0/4 but will only

 have effect when the interface is in a non-trunking mode.



10. Notice the message the switch provides when enabling portfast. Although it seems like the command did not take effect, as long as the port is in access mode (discussed in a minute), the port will now be in portfast mode.


11. After you make any changes you want to the interfaces, you can view the different interfaces with the show interface command. The switch output below shows the command used to view a 10/100BaseT interface on the 3550 switch.


3550A#sh int f0/4

FastEthernet0/4 is up, line protocol is up
  Hardware is Fast Ethernet, address is 00b0.c5e4.e2cf (bia 00b0.c5e4.e2cf)
  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)
  Full duplex, 100Mb/s
  input flow-control is off, output flow-control is off
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input never, output 1w6d, 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
     1 packets input, 64 bytes, 0 no buffer
     Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     0 watchdog, 0 multicast, 0 pause input
     0 input packets with dribble condition detected
     1 packets output, 64 bytes, 0 underruns
     0 output errors, 0 collisions, 3 interface resets
     0 babbles, 0 late collision, 0 deferred
     0 lost carrier, 0 no carrier, 0 PAUSE output
     0 output buffer failures, 0 output buffers swapped out



12. In addition to the show interface command, you can use the show running-config command to see the interface configuration as well.

3550A#sh run

[output cut]

interface FastEthernet0/3
  switchport mode dynamic desirable
interface FastEthernet0/4
  switchport mode dynamic desirable
  spanning-tree portfast
interface FastEthernet0/5

[output cut]


13. You can administratively set a name for each interface on the 3550 switch. Like the hostname, the descriptions are only locally significant. For the 3550 series switch, use the description command. You can use spaces with the description command, but you can use underlines if you need to.


To set the descriptions, you need to be in interface configuration mode. From interface configuration mode, use the description command to describe each interface.

3550A#config t

Enter configuration commands, one per line.  End with CTRL/Z

3550A(config)#int fa 0/4

3550A(config-if)#description Marketing VLAN

3550A(config-if)#int fa 0/10

3550A(config-if)#description trunk to Building 3


In the configuration example above, we set the description on both port 4 and 10.


14. Once you have configured the descriptions you want on each interface, you can then view the descriptions with either the show interface command, or show running-configcommand. View the configuration of the Ethernet interface 0/9 by using the show interface ethernet 0/4 command.


3550A#sh int  fa 0/4

FastEthernet0/4 is up, line protocol is up
Hardware is Fast Ethernet, address is 00b0.1a09.2097 (bia 00b0.1a09.2097)
Description: Marketing VLAN

(output cut)


15. Use the show running-config command to view the interface configurations as well.

3550A#sh run

[output cut]


interface FastEthernet0/4
description "Marketing VLAN"
duplex full
speed 100
spanning-tree portfast


[output cut]

Notice in the above switch output that the sh int fa0/4 command and the show run command both show the description command set on an interface.

 ---Original reading at content.digiex.net

More Cisco 3560 Tutorials and Tips:

How to Configure Interfaces for the 3560 Switch?

How to Configure the Cisco Catalyst 3560 Series Switches?

Video Offer: Cisco Catalyst 3560 and 3750 QoS Simplified

How to Save/Keep the Cisco 3560 Switch Configuration?

Why Should We Care about Cisco 3560-E Series Switches

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