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Sat, Jan 01, 2022 10:33 pm

Setting the date and time on a Cisco switch

When I logged into an old Cisco 2950 network switch today and checked the time on the switch, I found the date was July 29, 1993 rather than January 1, 2022.

Hoggle>show clock
*23:47:16.884 UTC Thu Jul 29 1993

A show clock detail command revealed there was no time source set for the switch.

Hoggle>show clock detail
*23:49:39.464 UTC Thu Jul 29 1993
No time source

To set the time, I turned on the ability to enter privileged commands with the enable command.


I set the date and time to the current Coordinated Universal Time (UTC) values with the clock set command. You can find the current UTC time at Current UTC, Time Zone (Coordinated Universal Time).

Hoggle#clock set 02:47:10 jan 2 2022
Hoggle#show clock
02:47:20.163 UTC Sun Jan 2 2022

The format of the command is clock set [hh:mm:ss] [month] [day] [year] with the following permissible values:

  1. hh:mm:ss - Specifies the current time in hours in military format, aka 24-hour clock format, minutes, and seconds. So the value for hours can range from 0 to 23 while the values for minutes and seconds can range from 0 to 59.
  2. month - Specifies the current month using the first three letters of the month name. The range is from Jan (January) to Dec (December).
  3. day - Specifies the current day of the month from 1 to 31
  4. year - Specifies the current year as a 4-digit year. The range is from 2000 up to 2037.

You may prefer to have the time displayed in your local time. This switch is in the Eastern Time Zone of the United States (you can see the current time for U.S. time zones at UNITED STATES TIME ZONES), so the local time is currently 5 hours behind UTC time. To display the time in the local time zone, I entered the configure terminal command to enter the Global Configuration context and then specified the timezone as EST and indicated it is minus 5 hours from UTC time.

Hoggle#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
Hoggle(config)#clock timezone EST -5

The format for the command is clock timezone [zone] [hours-offset] [minutes-offset]. The options for the command are as follows:

  1. zone - The acronym of the time zone, which can be up to four characters in length.
  2. hours-offset - The hours difference from UTC. The range is from -12 to +13.
  3. minutes-offset - (Optional) The minutes difference from UTC. The range is from 0 to 59.

You can exit the Global Configuration context with Ctrl-Z. If you then issue the show clock command you should see the date and time matching your local time.

Hoggle#show clock
22:17:01.987 EST Sat Jan 1 2022

[/hardware/network/switch/cisco] permanent link

Sat, Jun 17, 2017 8:02 pm

Clearing the counters for a port on a Cisco switch

You can view the counters for a port on a Cisco switch using the show interfaces command. E.g., if I want to check on whether cyclic redundancy check (CRC) errors have been occurring on port fa0/16, I can issue the command shown below:

Huron>show interfaces fa0/16
FastEthernet0/16 is up, line protocol is up (connected)
  Hardware is Fast Ethernet, address is 0009.e897.d290 (bia 0009.e897.d290)
  MTU 1500 bytes, BW 10000 Kbit, DLY 1000 usec,
     reliability 255/255, txload 19/255, rxload 1/255
  Encapsulation ARPA, loopback not set
  Keepalive set (10 sec)
  Full-duplex, 10Mb/s, media type is 100BaseTX
  input flow-control is unsupported output flow-control is unsupported
  ARP type: ARPA, ARP Timeout 04:00:00
  Last input never, output 00:00:00, output hang never
  Last clearing of "show interface" counters 2d17h
  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 24000 bits/sec, 40 packets/sec
  5 minute output rate 756000 bits/sec, 64 packets/sec
     46168 packets input, 4608074 bytes, 0 no buffer
     Received 1250 broadcasts (1161 multicast)
     0 runts, 0 giants, 0 throttles
     121 input errors, 16 CRC, 105 frame, 0 overrun, 0 ignored
     0 watchdog, 1161 multicast, 0 pause input
     0 input packets with dribble condition detected
     255151 packets output, 119141892 bytes, 0 underruns
     0 output errors, 0 collisions, 0 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

[ More Info ]

[/hardware/network/switch/cisco] permanent link

Thu, Jun 15, 2017 11:26 pm

Changing the duplex setting for a port on a Cisco switch

You can determine the speed and duplex settings for a port on a Cisco switch with the show interfces port_designation status. E.g.:

Huron>show interfaces fa0/1 status

Port      Name               Status       Vlan       Duplex  Speed Type
Fa0/1                        connected    1            full     10 10/100BaseTX

Often ports will be set to autonegotiate the speed and duplex settings with the equipment connected to the port. But sometimes that autonegotiation process may not work as expected requiring you to manually set the parameters. E.g, if the piece of equipment being connected to the port on the Cisco switch is configured for a fixed mode of operation while the port on the switch is configured for autonegotiate, the speeds may be configured for matching values on both sides but there may be a duplex mismatch. As a result of that mismatch cyclic redundancy check (CRC) errors may be reported for the port on the switch. You can manually set the duplex setting by entering the enable command and then the enable password when prompted. Then enter the configure command and then enter duplex followed by full or half, e.g., duplex full.

[/hardware/network/switch/cisco] permanent link

Sun, Jun 19, 2016 10:44 pm

Determining the port to which a system is connected by MAC address

If you need to know the port on a Cisco switch to which a particular host is connected and know the media access control (MAC) address, you can determine the port to which it connects using a show mac address-table address command. You can view all of the entries in the MAC address table with the command show mac address-table, but if you know the MAC address of the relevant system and only wish to determine the port on the switch to which it connects, you can specify its MAC address with the command show mac address-table address followed by the 48-bit MAC address, which can be in the form xx.xx.xx.xx.xx.xx or xxxx.xxxx.xxxx .
Saturn>show mac address-table address 50:e5:49:d8:13:37
          Mac Address Table

Vlan    Mac Address       Type        Ports
----    -----------       --------    -----
   1    50e5.49d8.1337    DYNAMIC     Fa0/19
Total Mac Addresses for this criterion: 1

With the port number, you can determine details for the interface to which the system connects using a show interfaces port where port is the port identified by the show mac address-table address command.

[ More Info ]

[/hardware/network/switch/cisco] permanent link

Tue, Mar 22, 2011 10:47 pm

Dealing with an err-disabled port

I experienced a problem with a Cisco switch periodically putting one port in an err-disabled state. After checking the port, I found that I needed to configure the speed and duplex settings to specific values rather than letting them be autonegotiated.

[ More Info ]

[/hardware/network/switch/cisco] permanent link

Sat, Dec 19, 2009 2:59 pm

Port Spanning

Cisco switches have the capability to mirror what is going to/from one port on a switch to another port on the same switch for monitoring purposes. Cisco dubs this mirroring capability "port spanning". The monitor command can be used to have all of the data to and from a particular port copied to another port of your choosing on the switch.

[More Info]

[/hardware/network/switch/cisco] permanent link

Thu, Nov 12, 2009 10:00 pm

Checking MAC Addresses on a Cisco Switch

On a Cisco switch, you can use the show mac address-table command to view the MAC addresses of devices connected to the switch.

[ More Info ]

[/hardware/network/switch/cisco] permanent link

Sun, Jul 26, 2009 1:13 pm

Cisco 2950 Switch Configuration

I set up a Cisco 2950 network switch this weekend using the Basic Management Setup process, which consists of answering a series of short questions posed by the switch in order to create a basic configuration for the switch. The steps are listed here.

[/hardware/network/switch/cisco] permanent link

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