Software Configuration Guide, Cisco IOS Release 15.2(2)E (Catalyst 2960, 2960-S, 2960-SF and 2960-Plus Switches)
Administering the Switch
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Administering the Switch

Contents

Administering the Switch

Finding Feature Information

Your software release may not support all the features documented in this module. For the latest caveats and feature information, see Bug Search Tool and the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the feature information table at the end of this module.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to http:/​/​www.cisco.com/​go/​cfn. An account on Cisco.com is not required.

Information About Administering the Switch

System Time and Date Management

You can manage the system time and date on your switch using automatic configuration methods (RTC and NTP), or manual configuration methods.


Note


For complete syntax and usage information for the commands used in this section, see the Cisco IOS Configuration Fundamentals Command Referenceon Cisco.com.


System Clock

The basis of the time service is the system clock. This clock runs from the moment the system starts up and keeps track of the date and time.

The system clock can then be set from these sources:

  • NTP

  • Manual configuration

The system clock can provide time to these services:

  • User show commands

  • Logging and debugging messages

The system clock keeps track of time internally based on Coordinated Universal Time (UTC), also known as Greenwich Mean Time (GMT). You can configure information about the local time zone and summer time (daylight saving time) so that the time appears correctly for the local time zone.

The system clock keeps track of whether the time is authoritative or not (that is, whether it has been set by a time source considered to be authoritative). If it is not authoritative, the time is available only for display purposes and is not redistributed. For configuration information, see the Configuring Time and Date Manually section.

Network Time Protocol

The NTP is designed to time-synchronize a network of devices. NTP runs over User Datagram Protocol (UDP), which runs over IP. NTP is documented in RFC 1305.

An NTP network usually gets its time from an authoritative time source, such as a radio clock or an atomic clock attached to a time server. NTP then distributes this time across the network. NTP is extremely efficient; no more than one packet per minute is necessary to synchronize two devices to within a millisecond of one another.

NTP uses the concept of a stratum to describe how many NTP hops away a device is from an authoritative time source. A stratum 1 time server has a radio or atomic clock directly attached, a stratum 2 time server receives its time through NTP from a stratum 1 time server, and so on. A device running NTP automatically chooses as its time source the device with the lowest stratum number with which it communicates through NTP. This strategy effectively builds a self-organizing tree of NTP speakers.

NTP avoids synchronizing to a device whose time might not be accurate by never synchronizing to a device that is not synchronized. NTP also compares the time reported by several devices and does not synchronize to a device whose time is significantly different than the others, even if its stratum is lower.

The communications between devices running NTP (known as associations) are usually statically configured; each device is given the IP address of all devices with which it should form associations. Accurate timekeeping is possible by exchanging NTP messages between each pair of devices with an association. However, in a LAN environment, NTP can be configured to use IP broadcast messages instead. This alternative reduces configuration complexity because each device can simply be configured to send or receive broadcast messages. However, in that case, information flow is one-way only.

The time kept on a device is a critical resource; you should use the security features of NTP to avoid the accidental or malicious setting of an incorrect time. Two mechanisms are available: an access list-based restriction scheme and an encrypted authentication mechanism.

Cisco’s implementation of NTP does not support stratum 1 service; it is not possible to connect to a radio or atomic clock. We recommend that the time service for your network be derived from the public NTP servers available on the IP Internet.

The Figure shows a typical network example using NTP. Switch A is the NTP master, with the Switch B, C, and D configured in NTP server mode, in server association with Switch A. Switch E is configured as an NTP peer to the upstream and downstream Switch, Switch B and Switch F, respectively.

Figure 1. Typical NTP Network Configuration



If the network is isolated from the Internet, Cisco’s implementation of NTP allows a device to act as if it is synchronized through NTP, when in fact it has learned the time by using other means. Other devices then synchronize to that device through NTP.

When multiple sources of time are available, NTP is always considered to be more authoritative. NTP time overrides the time set by any other method.

Several manufacturers include NTP software for their host systems, and a publicly available version for systems running UNIX and its various derivatives is also available. This software allows host systems to be time-synchronized as well.

NTP Version 4

NTP version 4 is implemented on the switch. NTPv4 is an extension of NTP version 3. NTPv4 supports both IPv4 and IPv6 and is backward-compatible with NTPv3.

NTPv4 provides these capabilities:

  • Support for IPv6.

  • Improved security compared to NTPv3. The NTPv4 protocol provides a security framework based on public key cryptography and standard X509 certificates.

  • Automatic calculation of the time-distribution hierarchy for a network. Using specific multicast groups, NTPv4 automatically configures the hierarchy of the servers to achieve the best time accuracy for the lowest bandwidth cost. This feature leverages site-local IPv6 multicast addresses.


Note


You can disable NTP packets from being received on routed ports and VLAN interfaces. You cannot disable NTP packets from being received on access ports. For details, see the Disabling NTPv4 Services on a Specific Interface section of the Implementing NTPv4 in IPv6 chapter of the Cisco IOS IPv6 Configuration Guide, Release 12.4T.

For details about configuring NTPv4, see the Implementing NTPv4 in IPv6 chapter of the Cisco IOS IPv6 Configuration Guide, Release 12.4T.

Configuring Time and Date Manually

If no other source of time is available, you can manually configure the time and date after the system is restarted. The time remains accurate until the next system restart. We recommend that you use manual configuration only as a last resort. If you have an outside source to which the Switch can synchronize, you do not need to manually set the system clock.

These sections contain this configuration information:

  • Setting the System Clock

  • Displaying the Time and Date Configuration

  • Configuring the Time Zone

  • Configuring Summer Time (Daylight Saving Time)

Setting the System Clock

If you have an outside source on the network that provides time services, such as an NTP server, you do not need to manually set the system clock.

Follow these steps to set the system clock:

SUMMARY STEPS

    1.    enable

    2.    Use one of the following:

    • clock set hh:mm:ss day month year
    • clock set hh:mm:ss month day year


DETAILED STEPS
     Command or ActionPurpose
    Step 1 enable


    Example:
    Switch> enable
    
    
     

    Enables privileged EXEC mode. Enter your password if prompted.

     

    Step 2Use one of the following:
    • clock set hh:mm:ss day month year
    • clock set hh:mm:ss month day year


    Example:
    
    Switch# clock set 13:32:00 23 March 2013
    
    
     

    Manually set the system clock using one of these formats:

    • hh:mm:ss—Specifies the time in hours (24-hour format), minutes, and seconds. The time specified is relative to the configured time zone.

    • day—Specifies the day by date in the month.

    • month—Specifies the month by name.

    • year—Specifies the year (no abbreviation).

     
    Related Concepts

    Displaying the Time and Date Configuration

    To display the time and date configuration, use the show clock[detail] privileged EXEC command.

    The system clock keeps an authoritative flag that shows whether the time is authoritative (believed to be accurate). If the system clock has been set by a timing source such as NTP, the flag is set. If the time is not authoritative, it is used only for display purposes. Until the clock is authoritative and the authoritative flag is set, the flag prevents peers from synchronizing to the clock when the peers’ time is invalid.

    The symbol that precedes the show clock display has this meaning:

    • *—Time is not authoritative.
    • (blank)—Time is authoritative.
    • .—Time is authoritative, but NTP is not synchronized.

    Configuring the Time Zone

    Follow these steps to manually configure the time zone:
    SUMMARY STEPS

      1.    enable

      2.    configure terminal

      3.    clock timezone zone hours-offset [minutes-offset]

      4.    end

      5.    show running-config

      6.    copy running-config startup-config


    DETAILED STEPS
       Command or ActionPurpose
      Step 1 enable


      Example:
      Switch> enable
      
      
       

      Enables privileged EXEC mode. Enter your password if prompted.

       

      Step 2configure terminal


      Example:
      
      Switch# configure terminal
      
      
       

      Enters the global configuration mode.

       
      Step 3clock timezone zone hours-offset [minutes-offset]


      Example:
      
      Switch(config)# clock timezone AST -3 30
      
      
       

      Sets the time zone.

      Internal time is kept in Coordinated Universal Time (UTC), so this command is used only for display purposes and when the time is manually set.

      • zone—Enters the name of the time zone to be displayed when standard time is in effect. The default is UTC.

      • hours-offset—Enters the hours offset from UTC.

      • (Optional) minutes-offset—Enters the minutes offset from UTC. This available where the local time zone is a percentage of an hour different from UTC.

       
      Step 4end


      Example:
      
      Switch(config)# end
      
      
       

      Returns to privileged EXEC mode.

       
      Step 5show running-config


      Example:
      
      Switch# show running-config 
      
      
       

      Verifies your entries.

       
      Step 6copy running-config startup-config


      Example:
      Switch# copy running-config startup-config 
      
      
       

      (Optional) Saves your entries in the configuration file.

       
      What to Do Next

      The minutes-offset variable in the clock timezone global configuration command is available for those cases where a local time zone is a percentage of an hour different from UTC. For example, the time zone for some sections of Atlantic Canada (AST) is UTC-3.5, where the 3 means 3 hours and.5 means 50 percent. In this case, the necessary command is clock timezone AST -3 30.

      To set the time to UTC, use the no clock timezone global configuration command.

      Related Information

      Configuring Summer Time (Daylight Saving Time)

      The first part of the clock summer-time global configuration command specifies when summer time begins, and the second part specifies when it ends. All times are relative to the local time zone. The start time is relative to standard time. The end time is relative to summer time. If the starting month is after the ending month, the system assumes that you are in the southern hemisphere.

      To configure summer time (daylight saving time) in areas where it starts and ends on a particular day of the week each year, perform this task:

      SUMMARY STEPS

        1.    enable

        2.    configure terminal

        3.    clock summer-time zone date date month year hh:mm date month year hh:mm [offset]]

        4.    clock summer-time zone recurring [week day month hh:mm week day month hh:mm [offset]]

        5.    end

        6.    show running-config

        7.    copy running-config startup-config


      DETAILED STEPS
         Command or ActionPurpose
        Step 1 enable


        Example:
        Switch> enable
        
        
         

        Enables privileged EXEC mode. Enter your password if prompted.

         

        Step 2configure terminal


        Example:
        
        Switch# configure terminal
        
        
         

        Enters the global configuration mode.

         
        Step 3clock summer-time zone date date month year hh:mm date month year hh:mm [offset]]


        Example:
        Switch(config)# clock summer-time PDT date 
        10 March 2013 2:00 3 November 2013 2:00
        
        
         

        Configures summer time to start and end on specified days every year.

         

        Step 4clock summer-time zone recurring [week day month hh:mm week day month hh:mm [offset]]


        Example:
        
        Switch(config)# clock summer-time 
        PDT recurring 10 March 2013 2:00 3 November 2013 2:00
        
        
         

        Configures summer time to start and end on the specified days every year. All times are relative to the local time zone. The start time is relative to standard time.

        The end time is relative to summer time. Summer time is disabled by default. If you specify clock summer-time zone recurring without parameters, the summer time rules default to the United States rules.

        If the starting month is after the ending month, the system assumes that you are in the southern hemisphere.

        • zone—Specifies the name of the time zone (for example, PDT) to be displayed when summer time is in effect.

        • (Optional) week— Specifies the week of the month (1 to 4, first, or last).

        • (Optional) day—Specifies the day of the week (Sunday, Monday...).

        • (Optional) month—Specifies the month (January, February...).

        • (Optional) hh:mm—Specifies the time (24-hour format) in hours and minutes.

        • (Optional) offset—Specifies the number of minutes to add during summer time. The default is 60.

         
        Step 5end


        Example:
        
        Switch(config)# end
        
        
         

        Returns to privileged EXEC mode.

         
        Step 6show running-config


        Example:
        
        Switch# show running-config 
        
        
         

        Verifies your entries.

         
        Step 7copy running-config startup-config


        Example:
        Switch# copy running-config startup-config 
        
        
         

        (Optional) Saves your entries in the configuration file.

         

        The first part of the clock summer-time global configuration command specifies when summer time begins, and the second part specifies when it ends. All times are relative to the local time zone. The start time is relative to standard time. The end time is relative to summer time. If the starting month is after the ending month, the system assumes that you are in the southern hemisphere. To disable summer time, use the no clock summer-time global configuration command.

        Follow these steps if summer time in your area does not follow a recurring pattern (configure the exact date and time of the next summer time events):

        SUMMARY STEPS

          1.    enable

          2.    configure terminal

          3.    clock summer-time zone date[ month date year hh:mm month date year hh:mm [offset]]orclock summer-time zone date [date month year hh:mm date month year hh:mm [offset]]

          4.    end

          5.    show running-config

          6.    copy running-config startup-config


        DETAILED STEPS
           Command or ActionPurpose
          Step 1 enable


          Example:
          Switch> enable
          
          
           

          Enables privileged EXEC mode. Enter your password if prompted.

           

          Step 2configure terminal


          Example:
          
          Switch# configure terminal
          
          
           

          Enters the global configuration mode.

           
          Step 3clock summer-time zone date[ month date year hh:mm month date year hh:mm [offset]]orclock summer-time zone date [date month year hh:mm date month year hh:mm [offset]]  

          Configures summer time to start on the first date and end on the second date.

          Summer time is disabled by default.
          • For zone, specify the name of the time zone (for example, PDT) to be displayed when summer time is in effect.

          • (Optional) For week, specify the week of the month (1 to 5 or last).

          • (Optional) For day, specify the day of the week (Sunday, Monday...).

          • (Optional) For month, specify the month (January, February...).

          • (Optional) For hh:mm, specify the time (24-hour format) in hours and minutes.

          • (Optional) For offset, specify the number of minutes to add during summer time. The default is 60.

           
          Step 4end


          Example:
          
          Switch(config)# end
          
          
           

          Returns to privileged EXEC mode.

           
          Step 5show running-config


          Example:
          
          Switch# show running-config 
          
          
           

          Verifies your entries.

           
          Step 6copy running-config startup-config


          Example:
          Switch# copy running-config startup-config 
          
          
           

          (Optional) Saves your entries in the configuration file.

           

          System Name and Prompt

          You configure the system name on the Switch to identify it. By default, the system name and prompt are Switch.

          If you have not configured a system prompt, the first 20 characters of the system name are used as the system prompt. A greater-than symbol [>] is appended. The prompt is updated whenever the system name changes.

          For complete syntax and usage information for the commands used in this section, see the Cisco IOS Configuration Fundamentals Command Reference, Release 12.4 and the Cisco IOS IP Command Reference, Volume 2 of 3: Routing Protocols, Release 12.4.

          Default System Name and Prompt Configuration

          The default Switch system name and prompt is Switch.

          Configuring a System Name

          Follow these steps to manually configure a system name:
          SUMMARY STEPS

            1.    enable

            2.    configure terminal

            3.    hostname name

            4.    end

            5.    show running-config

            6.    copy running-config startup-config


          DETAILED STEPS
             Command or ActionPurpose
            Step 1 enable


            Example:
            Switch> enable
            
            
             

            Enables privileged EXEC mode. Enter your password if prompted.

             

            Step 2configure terminal


            Example:
            
            Switch# configure terminal
            
            
             

            Enters the global configuration mode.

             
            Step 3hostname name


            Example:
            
            Switch(config)# hostname 
            remote-users
            
            
             

            Configures a system name. When you set the system name, it is also used as the system prompt.

            The default setting is Switch.

            The name must follow the rules for ARPANET hostnames. They must start with a letter, end with a letter or digit, and have as interior characters only letters, digits, and hyphens. Names can be up to 63 characters.

             
            Step 4end


            Example:
            
            Switch(config)# end
            
            
             

            Returns to privileged EXEC mode.

             
            Step 5show running-config


            Example:
            
            Switch# show running-config 
            
            
             

            Verifies your entries.

             
            Step 6copy running-config startup-config


            Example:
            Switch# copy running-config startup-config 
            
            
             

            (Optional) Saves your entries in the configuration file.

             

            DNS

            The DNS protocol controls the Domain Name System (DNS), a distributed database with which you can map hostnames to IP addresses. When you configure DNS on your switch, you can substitute the hostname for the IP address with all IP commands, such as ping, telnet, connect, and related Telnet support operations.

            IP defines a hierarchical naming scheme that allows a device to be identified by its location or domain. Domain names are pieced together with periods (.) as the delimiting characters. For example, Cisco Systems is a commercial organization that IP identifies by a com domain name, so its domain name is cisco.com. A specific device in this domain, for example, the File Transfer Protocol (FTP) system is identified as ftp.cisco.com.

            To keep track of domain names, IP has defined the concept of a domain name server, which holds a cache (or database) of names mapped to IP addresses. To map domain names to IP addresses, you must first identify the hostnames, specify the name server that is present on your network, and enable the DNS.

            Default DNS Settings



            Table 1 Default DNS Settings

            Feature

            Default Setting

            DNS enable state

            Enabled.

            DNS default domain name

            None configured.

            DNS servers

            No name server addresses are configured.

            Related Tasks
            Setting Up DNS

            If you use the switch IP address as its hostname, the IP address is used and no DNS query occurs. If you configure a hostname that contains no periods (.), a period followed by the default domain name is appended to the hostname before the DNS query is made to map the name to an IP address. The default domain name is the value set by the ip domain-name global configuration command. If there is a period (.) in the hostname, the Cisco IOS software looks up the IP address without appending any default domain name to the hostname.

            Follow these steps to set up your switch to use the DNS:

            SUMMARY STEPS

              1.    enable

              2.    configure terminal

              3.    ip domain-name name

              4.    ip name-server server-address1 [server-address2 ... server-address6]

              5.    ip domain-lookup [nsap | source-interface interface]

              6.    end

              7.    show running-config

              8.    copy running-config startup-config


            DETAILED STEPS
               Command or ActionPurpose
              Step 1 enable


              Example:
              Switch> enable
              
              
               

              Enables privileged EXEC mode. Enter your password if prompted.

               

              Step 2configure terminal


              Example:
              
              Switch# configure terminal
              
              
               

              Enters the global configuration mode.

               
              Step 3ip domain-name name


              Example:
              
              Switch(config)# ip domain-name Cisco.com
              
              
               

              Defines a default domain name that the software uses to complete unqualified hostnames (names without a dotted-decimal domain name).

              Do not include the initial period that separates an unqualified name from the domain name.

              At boot time, no domain name is configured; however, if the switch configuration comes from a BOOTP or Dynamic Host Configuration Protocol (DHCP) server, then the default domain name might be set by the BOOTP or DHCP server (if the servers were configured with this information).

               
              Step 4ip name-server server-address1 [server-address2 ... server-address6]


              Example:
              
              Switch(config)# ip 
              name-server 192.168.1.100 
              192.168.1.200 192.168.1.300
              
              
               

              Specifies the address of one or more name servers to use for name and address resolution.

              You can specify up to six name servers. Separate each server address with a space. The first server specified is the primary server. The switch sends DNS queries to the primary server first. If that query fails, the backup servers are queried.

               
              Step 5ip domain-lookup [nsap | source-interface interface]


              Example:
              
              Switch(config)# ip domain-lookup
              
              
               

              (Optional) Enables DNS-based hostname-to-address translation on your switch. This feature is enabled by default.

              If your network devices require connectivity with devices in networks for which you do not control name assignment, you can dynamically assign device names that uniquely identify your devices by using the global Internet naming scheme (DNS).

               
              Step 6end


              Example:
              
              Switch(config)# end
              
              
               

              Returns to privileged EXEC mode.

               
              Step 7show running-config


              Example:
              
              Switch# show running-config 
              
              
               

              Verifies your entries.

               
              Step 8copy running-config startup-config


              Example:
              Switch# copy running-config startup-config 
              
              
               

              (Optional) Saves your entries in the configuration file.

               
              What to Do Next

              To remove a domain name, use the no ip domain-name name global configuration command. To remove a name server address, use the no ip name-server server-address global configuration command. To disable DNS on the switch, use the no ip domain-lookup global configuration command.

              Related References
              Displaying the DNS Configuration

              To display the DNS configuration information, use the show running-config privileged EXEC command.

              Login Banners

              You can configure a message-of-the-day (MOTD) and a login banner. The MOTD banner is displayed on all connected terminals at login and is useful for sending messages that affect all network users (such as impending system shutdowns).

              The login banner is also displayed on all connected terminals. It appears after the MOTD banner and before the login prompts.


              Note


              For complete syntax and usage information for the commands used in this section, see the Cisco IOS Configuration Fundamentals Command Reference, Release 12.4.


              Default Banner Configuration

              The MOTD and login banners are not configured.

              Configuring a Message-of-the-Day Login Banner

              You can create a single or multiline message banner that appears on the screen when someone logs in to the switch

              Follow these steps to configure a MOTD login banner:

              SUMMARY STEPS

                1.    enable

                2.    configure terminal

                3.    banner motd c message c

                4.    end

                5.    show running-config

                6.    copy running-config startup-config


              DETAILED STEPS
                 Command or ActionPurpose
                Step 1 enable


                Example:
                Switch> enable
                
                
                 

                Enables privileged EXEC mode. Enter your password if prompted.

                 

                Step 2configure terminal


                Example:
                
                Switch# configure terminal
                
                
                 

                Enters the global configuration mode.

                 
                Step 3banner motd c message c


                Example:
                
                Switch(config)# banner motd # 
                This is a secure site. Only 
                authorized users are allowed.
                For access, contact technical 
                support.
                #
                
                
                 

                Specifies the message of the day.

                c—Enters the delimiting character of your choice, for example, a pound sign (#), and press the Return key. The delimiting character signifies the beginning and end of the banner text. Characters after the ending delimiter are discarded.

                message—Enters a banner message up to 255 characters. You cannot use the delimiting character in the message.

                 
                Step 4end


                Example:
                
                Switch(config)# end
                
                
                 

                Returns to privileged EXEC mode.

                 
                Step 5show running-config


                Example:
                
                Switch# show running-config 
                
                
                 

                Verifies your entries.

                 
                Step 6copy running-config startup-config


                Example:
                Switch# copy running-config startup-config 
                
                
                 

                (Optional) Saves your entries in the configuration file.

                 
                What to Do Next

                To delete the MOTD banner, use the no banner motd global configuration command.

                Configuring a Login Banner

                You can configure a login banner to be displayed on all connected terminals. This banner appears after the MOTD banner and before the login prompt.

                Follow these steps to configure a login banner:

                SUMMARY STEPS

                  1.    enable

                  2.    configure terminal

                  3.    banner login c message c

                  4.    end

                  5.    show running-config

                  6.    copy running-config startup-config


                DETAILED STEPS
                   Command or ActionPurpose
                  Step 1 enable


                  Example:
                  Switch> enable
                  
                  
                   

                  Enables privileged EXEC mode. Enter your password if prompted.

                   

                  Step 2configure terminal


                  Example:
                  
                  Switch# configure terminal
                  
                  
                   

                  Enters the global configuration mode.

                   
                  Step 3banner login c message c


                  Example:
                  Switch(config)# banner login $
                  Access for authorized users only. 
                  Please enter your username and 
                  password.
                  $
                  
                  
                   

                  Specifies the login message.

                  c— Enters the delimiting character of your choice, for example, a pound sign (#), and press the Return key. The delimiting character signifies the beginning and end of the banner text. Characters after the ending delimiter are discarded.

                  message—Enters a login message up to 255 characters. You cannot use the delimiting character in the message.

                   
                  Step 4end


                  Example:
                  
                  Switch(config)# end
                  
                  
                   

                  Returns to privileged EXEC mode.

                   
                  Step 5show running-config


                  Example:
                  
                  Switch# show running-config 
                  
                  
                   

                  Verifies your entries.

                   
                  Step 6copy running-config startup-config


                  Example:
                  Switch# copy running-config startup-config 
                  
                  
                   

                  (Optional) Saves your entries in the configuration file.

                   
                  What to Do Next

                  To delete the login banner, use the no banner login global configuration command.

                  Managing the MAC Address Table

                  MAC Address Table

                  The MAC address table contains address information that the switch uses to forward traffic between ports. All MAC addresses in the address table are associated with one or more ports. The address table includes these types of addresses:

                  • Dynamic address—A source MAC address that the switch learns and then ages when it is not in use.

                  • Static address—A manually entered unicast address that does not age and that is not lost when the switch resets.

                  The address table lists the destination MAC address, the associated VLAN ID, and port number associated with the address and the type (static or dynamic).


                  Note


                  For complete syntax and usage information for the commands used in this section, see the command reference for this release.


                  MAC Address Table Creation

                  With multiple MAC addresses supported on all ports, you can connect any port on the switch to other network devices. The switch provides dynamic addressing by learning the source address of packets it receives on each port and adding the address and its associated port number to the address table. As devices are added or removed from the network, the switch updates the address table, adding new dynamic addresses and aging out those that are not in use.

                  The aging interval is globally configured. However, the switch maintains an address table for each VLAN, and STP can accelerate the aging interval on a per-VLAN basis.

                  The switch sends packets between any combination of ports, based on the destination address of the received packet. Using the MAC address table, the switch forwards the packet only to the port associated with the destination address. If the destination address is on the port that sent the packet, the packet is filtered and not forwarded. The switch always uses the store-and-forward method: complete packets are stored and checked for errors before transmission.

                  MAC Addresses and VLANs

                  All addresses are associated with a VLAN. An address can exist in more than one VLAN and have different destinations in each. Unicast addresses, for example, could be forwarded to port 1 in VLAN 1 and ports 9, 10, and 1 in VLAN 5.

                  Each VLAN maintains its own logical address table. A known address in one VLAN is unknown in another until it is learned or statically associated with a port in the other VLAN.

                  Default MAC Address Table Settings

                  The following table shows the default settings for the MAC address table.

                  Table 2  Default Settings for the MAC Address

                  Feature

                  Default Setting

                  Aging time

                  300 seconds

                  Dynamic addresses

                  Automatically learned

                  Static addresses

                  None configured

                  Changing the Address Aging Time

                  Dynamic addresses are source MAC addresses that the switch learns and then ages when they are not in use. You can change the aging time setting for all VLANs or for a specified VLAN.

                  Setting too short an aging time can cause addresses to be prematurely removed from the table. Then when the switch receives a packet for an unknown destination, it floods the packet to all ports in the same VLAN as the receiving port. This unnecessary flooding can impact performance. Setting too long an aging time can cause the address table to be filled with unused addresses, which prevents new addresses from being learned. Flooding results, which can impact switch performance.

                  Follow these steps to configure the dynamic address table aging time:

                  SUMMARY STEPS

                    1.    enable

                    2.    configure terminal

                    3.    mac address-table aging-time [0 | 10-1000000] [routed-mac | vlan vlan-id]

                    4.    end

                    5.    show running-config

                    6.    copy running-config startup-config


                  DETAILED STEPS
                     Command or ActionPurpose
                    Step 1 enable


                    Example:
                    Switch> enable
                    
                    
                     

                    Enables privileged EXEC mode. Enter your password if prompted.

                     

                    Step 2configure terminal


                    Example:
                    
                    Switch# configure terminal
                    
                    
                     

                    Enters the global configuration mode.

                     
                    Step 3mac address-table aging-time [0 | 10-1000000] [routed-mac | vlan vlan-id]


                    Example:
                    
                    Switch(config)# mac address-table 
                    aging-time 500 vlan 2
                    
                    
                     

                    Sets the length of time that a dynamic entry remains in the MAC address table after the entry is used or updated.

                    The range is 10 to 1000000 seconds. The default is 300. You can also enter 0, which disables aging. Static address entries are never aged or removed from the table.

                    vlan-id—Valid IDs are 1 to 4094.

                     
                    Step 4end


                    Example:
                    
                    Switch(config)# end
                    
                    
                     

                    Returns to privileged EXEC mode.

                     
                    Step 5show running-config


                    Example:
                    
                    Switch# show running-config 
                    
                    
                     

                    Verifies your entries.

                     
                    Step 6copy running-config startup-config


                    Example:
                    Switch# copy running-config startup-config 
                    
                    
                     

                    (Optional) Saves your entries in the configuration file.

                     
                    What to Do Next

                    To return to the default value, use the no mac address-table aging-time global configuration command.

                    Removing Dynamic Address Entries

                    To remove all dynamic entries, use the clear mac address-table dynamic command in privileged EXEC mode. You can also remove a specific MAC address (clear mac address-table dynamic address mac- address), remove all addresses on the specified physical port or port channel (clear mac address-table dynamic interface interface-id), or remove all addresses on a specified VLAN (clear mac address-table dynamic vlan vlan-id).

                    To verify that dynamic entries have been removed, use the show mac address-table dynamic privileged EXEC command.

                    Configuring MAC Address Change Notification Traps

                    MAC address change notification tracks users on a network by storing the MAC address change activity. When the switch learns or removes a MAC address, an SNMP notification trap can be sent to the NMS. If you have many users coming and going from the network, you can set a trap-interval time to bundle the notification traps to reduce network traffic. The MAC notification history table stores MAC address activity for each port for which the trap is set. MAC address change notifications are generated for dynamic and secure MAC addresses. Notifications are not generated for self addresses, multicast addresses, or other static addresses.

                    Follow these steps to configure the switch to send MAC address change notification traps to an NMS host:

                    SUMMARY STEPS

                      1.    enable

                      2.    configure terminal

                      3.    snmp-server host host-addr community-string notification-type { informs | traps } {version {1 | 2c | 3}} {vrf vrf instance name}

                      4.    snmp-server enable traps mac-notification change

                      5.    mac address-table notification change

                      6.    mac address-table notification change [interval value] [history-size value]

                      7.    interface interface-id

                      8.    snmp trap mac-notification change {added | removed}

                      9.    end

                      10.    show running-config

                      11.    copy running-config startup-config


                    DETAILED STEPS
                       Command or ActionPurpose
                      Step 1 enable


                      Example:
                      Switch> enable
                      
                      
                       

                      Enables privileged EXEC mode. Enter your password if prompted.

                       

                      Step 2configure terminal


                      Example:
                      
                      Switch# configure terminal
                      
                      
                       

                      Enters the global configuration mode.

                       
                      Step 3snmp-server host host-addr community-string notification-type { informs | traps } {version {1 | 2c | 3}} {vrf vrf instance name}


                      Example:
                      
                      Switch(config)# snmp-server host 
                      172.20.10.10 traps private mac-notification
                       

                      Specifies the recipient of the trap message.

                      • host-addr—Specifies the name or address of the NMS.

                      • traps (the default)Sends SNMP traps to the host.

                      • informsSends SNMP informs to the host.

                      • versionSpecifies the SNMP version to support. Version 1, the default, is not available with informs.

                      • community-string—Specifies the string to send with the notification operation. Though you can set this string by using the snmp-server host command, we recommend that you define this string by using the snmp-server community command before using the snmp-server host command.

                      • notification-type—Uses the mac-notification keyword.

                      • vrf vrf instance nameSpecifies the VPN routing/forwarding instance for this host.

                       
                      Step 4snmp-server enable traps mac-notification change


                      Example:
                      
                      Switch(config)# snmp-server enable traps 
                      mac-notification change
                       

                      Enables the switch to send MAC address change notification traps to the NMS.

                       
                      Step 5mac address-table notification change


                      Example:
                      
                      Switch(config)# mac address-table 
                      notification change
                      
                      
                       

                      Enables the MAC address change notification feature.

                       
                      Step 6mac address-table notification change [interval value] [history-size value]


                      Example:
                      
                      Switch(config)# mac address-table 
                      notification change interval 123
                      Switch(config)#mac address-table 
                      notification change history-size 100
                      
                      
                       

                      Enters the trap interval time and the history table size.

                      • (Optional) interval value—Specifies the notification trap interval in seconds between each set of traps that are generated to the NMS. The range is 0 to 2147483647 seconds; the default is 1 second.

                      • (Optional) history-size value—Specifies the maximum number of entries in the MAC notification history table. The range is 0 to 500; the default is 1.

                       
                      Step 7interface interface-id


                      Example:
                      
                      Switch(config)# interface 
                      gigabitethernet1/0/2
                       

                      Enters interface configuration mode, and specifies the Layer 2 interface on which to enable the SNMP MAC address notification trap.

                       
                      Step 8snmp trap mac-notification change {added | removed}


                      Example:
                      
                      Switch(config-if)# snmp trap 
                      mac-notification change added
                       

                      Enables the MAC address change notification trap on the interface.

                      • Enables the trap when a MAC address is added on this interface.

                      • Enables the trap when a MAC address is removed from this interface.

                       
                      Step 9end


                      Example:
                      
                      Switch(config)# end
                      
                      
                       

                      Returns to privileged EXEC mode.

                       
                      Step 10show running-config


                      Example:
                      
                      Switch# show running-config 
                      
                      
                       

                      Verifies your entries.

                       
                      Step 11copy running-config startup-config


                      Example:
                      Switch# copy running-config startup-config 
                      
                      
                       

                      (Optional) Saves your entries in the configuration file.

                       
                      What to Do Next

                      To disable MAC address-change notification traps, use the no snmp-server enable traps mac-notification change global configuration command. To disable the MAC address-change notification traps on a specific interface, use the no snmp trap mac-notification change{added|removed} interface configuration command. To disable the MAC address-change notification feature, use the no mac address-table notification change global configuration command.

                      You can verify your settings by entering the show mac address-table notification change interface and the show mac address-table notification change privileged EXEC commands.

                      Configuring MAC Address Move Notification Traps

                      When you configure MAC-move notification, an SNMP notification is generated and sent to the network management system whenever a MAC address moves from one port to another within the same VLAN.

                      Follow these steps to configure the switch to send MAC address-move notification traps to an NMS host:

                      SUMMARY STEPS

                        1.    enable

                        2.    configure terminal

                        3.    snmp-server host host-addr {traps | informs} {version {1 | 2c | 3}} community-string notification-type

                        4.    snmp-server enable traps mac-notification move

                        5.    mac address-table notification mac-move

                        6.    end

                        7.    show running-config

                        8.    copy running-config startup-config


                      DETAILED STEPS
                         Command or ActionPurpose
                        Step 1 enable


                        Example:
                        Switch> enable
                        
                        
                         

                        Enables privileged EXEC mode. Enter your password if prompted.

                         

                        Step 2configure terminal


                        Example:
                        
                        Switch# configure terminal
                        
                        
                         

                        Enters the global configuration mode.

                         
                        Step 3snmp-server host host-addr {traps | informs} {version {1 | 2c | 3}} community-string notification-type


                        Example:
                        
                        Switch(config)# snmp-server host 
                        172.20.10.10 traps private mac-notification
                        
                        
                         

                        Specifies the recipient of the trap message.

                        • host-addr—Specifies the name or address of the NMS.

                        • traps (the default)Sends SNMP traps to the host.

                        • informsSends SNMP informs to the host.

                        • versionSpecifies the SNMP version to support. Version 1, the default, is not available with informs.

                        • community-string—Specifies the string to send with the notification operation. Though you can set this string by using the snmp-server host command, we recommend that you define this string by using the snmp-server community command before using the snmp-server host command.

                        • notification-type—Uses the mac-notification keyword.

                         
                        Step 4snmp-server enable traps mac-notification move


                        Example:
                        
                        Switch(config)# snmp-server enable traps 
                        mac-notification move
                        
                        
                         

                        Enables the switch to send MAC address move notification traps to the NMS.

                         
                        Step 5mac address-table notification mac-move


                        Example:
                        
                        Switch(config)# mac address-table 
                        notification mac-move
                        
                        
                         

                        Enables the MAC address move notification feature.

                         
                        Step 6end


                        Example:
                        
                        Switch(config)# end
                        
                        
                         

                        Returns to privileged EXEC mode.

                         
                        Step 7show running-config


                        Example:
                        
                        Switch# show running-config 
                        
                        
                         

                        Verifies your entries.

                         
                        Step 8copy running-config startup-config


                        Example:
                        Switch# copy running-config startup-config 
                        
                        
                         

                        (Optional) Saves your entries in the configuration file.

                         
                        What to Do Next

                        To disable MAC address-move notification traps, use the no snmp-server enable traps mac-notification move global configuration command. To disable the MAC address-move notification feature, use the no mac address-table notification mac-move global configuration command.

                        You can verify your settings by entering the show mac address-table notification mac-move privileged EXEC commands.

                        Configuring MAC Threshold Notification Traps

                        When you configure MAC threshold notification, an SNMP notification is generated and sent to the network management system when a MAC address table threshold limit is reached or exceeded.

                        Follow these steps to configure the switch to send MAC address table threshold notification traps to an NMS host:

                        SUMMARY STEPS

                          1.    enable

                          2.    configure terminal

                          3.    snmp-server host host-addr {traps | informs} {version {1 | 2c | 3}} community-string notification-type

                          4.    snmp-server enable traps mac-notification threshold

                          5.    mac address-table notification threshold

                          6.    mac address-table notification threshold [limit percentage] | [interval time]

                          7.    end

                          8.    show running-config

                          9.    copy running-config startup-config


                        DETAILED STEPS
                           Command or ActionPurpose
                          Step 1 enable


                          Example:
                          Switch> enable
                          
                          
                           

                          Enables privileged EXEC mode. Enter your password if prompted.

                           

                          Step 2configure terminal


                          Example:
                          
                          Switch# configure terminal
                          
                          
                           

                          Enters the global configuration mode.

                           
                          Step 3snmp-server host host-addr {traps | informs} {version {1 | 2c | 3}} community-string notification-type


                          Example:
                          
                          Switch(config)# snmp-server host 
                          172.20.10.10 traps private 
                          mac-notification
                          
                          
                           

                          Specifies the recipient of the trap message.

                          • host-addr—Specifies the name or address of the NMS.

                          • traps (the default)Sends SNMP traps to the host.

                          • informsSends SNMP informs to the host.

                          • versionSpecifies the SNMP version to support. Version 1, the default, is not available with informs.

                          • community-string—Specifies the string to send with the notification operation. You can set this string by using the snmp-server host command, but we recommend that you define this string by using the snmp-server community command before using the snmp-server host command.

                          • notification-type—Uses the mac-notification keyword.

                           
                          Step 4snmp-server enable traps mac-notification threshold


                          Example:
                          
                          Switch(config)# snmp-server enable traps 
                          mac-notification threshold
                          
                          
                           

                          Enables MAC threshold notification traps to the NMS.

                           
                          Step 5mac address-table notification threshold


                          Example:
                          
                          Switch(config)# mac address-table 
                          notification threshold
                          
                          
                           

                          Enables the MAC address threshold notification feature.

                           
                          Step 6mac address-table notification threshold [limit percentage] | [interval time]


                          Example:
                          
                          Switch(config)# mac address-table 
                          notification threshold interval 123
                          Switch(config)# mac address-table 
                          notification threshold limit 78
                          
                          
                           

                          Enters the threshold value for the MAC address threshold usage monitoring.

                          • (Optional) limit percentage—Specifies the percentage of the MAC address table use; valid values are from 1 to 100 percent. The default is 50 percent.

                          • (Optional) interval time—Specifies the time between notifications; valid values are greater than or equal to 120 seconds. The default is 120 seconds.

                           
                          Step 7end


                          Example:
                          
                          Switch(config)# end
                          
                          
                           

                          Returns to privileged EXEC mode.

                           
                          Step 8show running-config


                          Example:
                          
                          Switch# show running-config 
                          
                          
                           

                          Verifies your entries.

                           
                          Step 9copy running-config startup-config


                          Example:
                          Switch# copy running-config startup-config 
                          
                          
                           

                          (Optional) Saves your entries in the configuration file.

                           
                          What to Do Next

                          Adding and Removing Static Address Entries

                          A static address has these characteristics:
                          • It is manually entered in the address table and must be manually removed.

                          • It can be a unicast or multicast address.

                          • It does not age and is retained when the switch restarts.

                          You can add and remove static addresses and define the forwarding behavior for them. The forwarding behavior defines how a port that receives a packet forwards it to another port for transmission. Because all ports are associated with at least one VLAN, the switch acquires the VLAN ID for the address from the ports that you specify. You can specify a different list of destination ports for each source port.

                          A packet with a static address that arrives on a VLAN where it has not been statically entered is flooded to all ports and not learned.

                          You add a static address to the address table by specifying the destination MAC unicast address and the VLAN from which it is received. Packets received with this destination address are forwarded to the interface specified with the interface-id option.

                          Follow these steps to add a static address:

                          SUMMARY STEPS

                            1.    enable

                            2.    configure terminal

                            3.    mac address-table static mac-addr vlan vlan-id interface interface-id

                            4.    end

                            5.    show running-config

                            6.    copy running-config startup-config


                          DETAILED STEPS
                             Command or ActionPurpose
                            Step 1 enable


                            Example:
                            Switch> enable
                            
                            
                             

                            Enables privileged EXEC mode. Enter your password if prompted.

                             

                            Step 2configure terminal


                            Example:
                            
                            Switch# configure terminal
                            
                            
                             

                            Enters the global configuration mode.

                             
                            Step 3mac address-table static mac-addr vlan vlan-id interface interface-id


                            Example:
                            
                            Switch(config)# mac address-table 
                            static c2f3.220a.12f4 vlan 4 interface gigabitethernet 1/0/1 
                            
                            
                             

                            Adds a static address to the MAC address table.

                            • mac-addr—Specifies the destination MAC unicast address to add to the address table. Packets with this destination address received in the specified VLAN are forwarded to the specified interface.

                            • vlan-id—Specifies the VLAN for which the packet with the specified MAC address is received. Valid VLAN IDs are 1 to 4094.

                            • interface-id—Specifies the interface to which the received packet is forwarded. Valid interfaces include physical ports or port channels. For static multicast addresses, you can enter multiple interface IDs. For static unicast addresses, you can enter only one interface at a time, but you can enter the command multiple times with the same MAC address and VLAN ID.

                             
                            Step 4end


                            Example:
                            Switch(config)# end
                             

                            Returns to privileged EXEC mode. Alternatively, you can also press Ctrl-Z to exit global configuration mode.

                             
                            Step 5show running-config


                            Example:
                            
                            Switch# show running-config 
                            
                            
                             

                            Verifies your entries.

                             
                            Step 6copy running-config startup-config


                            Example:
                            Switch# copy running-config startup-config 
                            
                            
                             

                            (Optional) Saves your entries in the configuration file.

                             
                            What to Do Next

                            To remove static entries from the address table, use the no mac address-table static mac-addr vlan vlan-id [interface interface-id] global configuration command.

                            Configuring Unicast MAC Address Filtering Guidelines

                            When unicast MAC address filtering is enabled, the Switch drops packets with specific source or destination MAC addresses. This feature is disabled by default and only supports unicast static addresses.

                            Follow these guidelines when using this feature:
                            • Multicast MAC addresses, broadcast MAC addresses, and router MAC addresses are not supported. If you specify one of these addresses when entering the mac address-table static mac-addr vlan vlan-id drop global configuration command, one of these messages appears:
                              • Only unicast addresses can be configured to be dropped
                              • CPU destined address cannot be configured as drop address
                            • Packets that are forwarded to the CPU are also not supported.
                            • If you add a unicast MAC address as a static address and configure unicast MAC address filtering, the Switch either adds the MAC address as a static address or drops packets with that MAC address, depending on which command was entered last. The second command that you entered overrides the first command.

                            For example, if you enter the mac address-table static mac-addr vlan vlan-id interface interface-id global configuration command followed by the mac address-table static mac-addr vlan vlan-id drop command, the switch drops packets with the specified MAC address as a source or destination.

                            If you enter the mac address-table static mac-addr vlan vlan-id drop global configuration command followed by the mac address-table static mac-addr vlan vlan-id interface interface-id command, the switch adds the MAC address as a static address.

                            You enable unicast MAC address filtering and configure the switch to drop packets with a specific address by specifying the source or destination unicast MAC address and the VLAN from which it is received.

                            Configuring Unicast MAC Address Filtering

                            Follow these steps to configure the Switch to drop a source or destination unicast static address:

                            SUMMARY STEPS

                              1.    enable

                              2.    configure terminal

                              3.    mac address-table static mac-addr vlan vlan-id drop

                              4.    end

                              5.    show running-config

                              6.    copy running-config startup-config


                            DETAILED STEPS
                               Command or ActionPurpose
                              Step 1 enable


                              Example:
                              Switch> enable
                              
                              
                               

                              Enables privileged EXEC mode. Enter your password if prompted.

                               

                              Step 2configure terminal


                              Example:
                              
                              Switch# configure terminal
                              
                              
                               

                              Enters the global configuration mode.

                               
                              Step 3mac address-table static mac-addr vlan vlan-id drop


                              Example:
                              
                              Switch(config)# mac address-table 
                              static c2f3.220a.12f4 vlan 4 drop
                              
                              
                               

                              Enables unicast MAC address filtering and configure the switch to drop a packet with the specified source or destination unicast static address.

                              • mac-addr—Specifies a source or destination unicast MAC address (48-bit). Packets with this MAC address are dropped.

                              • vlan-id—Specifies the VLAN for which the packet with the specified MAC address is received. Valid VLAN IDs are 1 to 4094.

                               
                              Step 4end


                              Example:
                              
                              Switch(config)# end
                              
                              
                               

                              Returns to privileged EXEC mode.

                               
                              Step 5show running-config


                              Example:
                              
                              Switch# show running-config 
                              
                              
                               

                              Verifies your entries.

                               
                              Step 6copy running-config startup-config


                              Example:
                              Switch# copy running-config startup-config 
                              
                              
                               

                              (Optional) Saves your entries in the configuration file.

                               

                              Disabling MAC Address Learning on a VLAN Guidelines

                              By default, MAC address learning is enabled on all VLANs on the Switch. You can control MAC address learning on a VLAN to manage the available MAC address table space by controlling which VLANs, and therefore which ports, can learn MAC addresses. Before you disable MAC address learning, be sure that you are familiar with the network topology and the switch system configuration. Disabling MAC address learning on a VLAN could cause flooding in the network.

                              Follow these guidelines when disabling MAC address learning on a VLAN:

                              • Use caution before disabling MAC address learning on a VLAN with a configured Switch virtual interface (SVI). The Switch then floods all IP packets in the Layer 2 domain.
                              • You can disable MAC address learning on a single VLAN ID (for example, no mac address-table learning vlan 223) or on a range of VLAN IDs (for example, no mac address-table learning vlan 1-20, 15.)
                              • We recommend that you disable MAC address learning only in VLANs with two ports. If you disable MAC address learning on a VLAN with more than two ports, every packet entering the Switch is flooded in that VLAN domain.
                              • You cannot disable MAC address learning on a VLAN that is used internally by the Switch. If the VLAN ID that you enter is an internal VLAN, the Switch generates an error message and rejects the command. To view internal VLANs in use, enter the show vlan internal usage privileged EXEC command.
                              • If you disable MAC address learning on a VLAN configured as a private-VLAN primary VLAN, MAC addresses are still learned on the secondary VLAN that belongs to the private VLAN and are then replicated on the primary VLAN. If you disable MAC address learning on the secondary VLAN, but not the primary VLAN of a private VLAN, MAC address learning occurs on the primary VLAN and is replicated on the secondary VLAN.
                              • You cannot disable MAC address learning on an RSPAN VLAN. The configuration is not allowed.
                              • If you disable MAC address learning on a VLAN that includes a secure port, MAC address learning is not disabled on that port. If you disable port security, the configured MAC address learning state is enabled.

                              Disabling MAC Address Learning on a VLAN

                              Follow these steps to disable MAC address learning on a VLAN:

                              SUMMARY STEPS

                                1.    enable

                                2.    configure terminal

                                3.    configure terminal

                                4.    no mac address-table learning vlan vlan-id

                                5.    end

                                6.    show mac address-table learning[vlanvlan-id]

                                7.    show running-config

                                8.    copy running-config startup-config


                              DETAILED STEPS
                                 Command or ActionPurpose
                                Step 1 enable


                                Example:
                                Switch> enable
                                
                                
                                 

                                Enables privileged EXEC mode. Enter your password if prompted.

                                 

                                Step 2configure terminal


                                Example:
                                
                                Switch# configure terminal
                                
                                
                                 

                                Enters the global configuration mode.

                                 
                                Step 3configure terminal
                                 

                                Enter global configuration mode.

                                 
                                Step 4no mac address-table learning vlan vlan-id
                                 

                                Disable MAC address learning on the specified VLAN or VLANs. You can specify a single VLAN ID or a range of VLAN IDs separated by a hyphen or comma. Valid VLAN IDs are 1 to 4094.

                                 
                                Step 5end


                                Example:
                                
                                Switch(config)# end
                                
                                
                                 

                                Returns to privileged EXEC mode.

                                 
                                Step 6show mac address-table learning[vlanvlan-id]
                                 
                                 
                                Step 7show running-config


                                Example:
                                
                                Switch# show running-config 
                                
                                
                                 

                                Verifies your entries.

                                 
                                Step 8copy running-config startup-config


                                Example:
                                Switch# copy running-config startup-config 
                                
                                
                                 

                                (Optional) Saves your entries in the configuration file.

                                 
                                What to Do Next

                                To reenable MAC address learning on a VLAN. use the default mac address-table learning vlanvlan-id global configuration command. You can also reenable MAC address learning on a VLAN by entering the the mac address-table learning vlan vlan-id global configuration command. The first(default) command returns to a default condition and therefore does not appear in the output from the show running-configcommand. The second command causes the configuration to appear in the show running-config privileged EXEC command display.

                                Switch(config)# no mac address-table learning vlan 200

                                You can display the MAC address learning status of all VLANs or a specified VLAN by entering theshow mac-address-table learning [vlan vlan-id] privileged EXEC command.

                                Displaying Address Table Entries

                                You can display the MAC address table by using one or more of the privileged EXEC commands described in this table:

                                Table 3 Commands for Displaying the MAC Address Table

                                Command

                                Description

                                show ip igmp snooping groups

                                Displays the Layer 2 multicast entries for all VLANs or the specified VLAN.

                                show mac address-table address

                                Displays MAC address table information for the specified MAC address.

                                show mac address-table aging-time

                                Displays the aging time in all VLANs or the specified VLAN.

                                show mac address-table count

                                Displays the number of addresses present in all VLANs or the specified VLAN.

                                show mac address-table dynamic

                                Displays only dynamic MAC address table entries.

                                show mac address-table interface

                                Displays the MAC address table information for the specified interface.

                                show mac address-table learning

                                Displays MAC address learning status of all VLANs or the specified VLAN.

                                show mac address-table notification

                                Displays the MAC notification parameters and history table.

                                show mac address-table static

                                Displays only static MAC address table entries.

                                show mac address-table vlan

                                Displays the MAC address table information for the specified VLAN.

                                ARP Table Management

                                To communicate with a device (over Ethernet, for example), the software first must learn the 48-bit MAC address or the local data link address of that device. The process of learning the local data link address from an IP address is called address resolution.

                                The Address Resolution Protocol (ARP) associates a host IP address with the corresponding media or MAC addresses and the VLAN ID. Using an IP address, ARP finds the associated MAC address. When a MAC address is found, the IP-MAC address association is stored in an ARP cache for rapid retrieval. Then the IP datagram is encapsulated in a link-layer frame and sent over the network. Encapsulation of IP datagrams and ARP requests and replies on IEEE 802 networks other than Ethernet is specified by the Subnetwork Access Protocol (SNAP). By default, standard Ethernet-style ARP encapsulation (represented by the arpa keyword) is enabled on the IP interface.

                                ARP entries added manually to the table do not age and must be manually removed.

                                For CLI procedures, see the Cisco IOS Release 12.4 documentation on Cisco.com.

                                Configuration Examples for Switch Administration

                                Example: Setting the System Clock

                                This example shows how to manually set the system clock:

                                Switch# clock set 13:32:00 23 July 2013
                                Related Concepts

                                Examples: Configuring Summer Time

                                This example (for daylight savings time) shows how to specify that summer time starts on March 10 at 02:00 and ends on November 3 at 02:00:

                                Switch(config)# clock summer-time PDT recurring PST date 
                                10 March 2013 2:00 3 November 2013 2:00
                                
                                

                                This example shows how to set summer time start and end dates:

                                Switch(config)#clock summer-time PST date 
                                20 March 2013 2:00 20 November 2013 2:00

                                Example: Configuring a MOTD Banner

                                This example shows how to configure a MOTD banner by using the pound sign (#) symbol as the beginning and ending delimiter:

                                 
                                Switch(config)# banner motd #
                                
                                This is a secure site. Only authorized users are allowed.
                                For access, contact technical support.
                                
                                #
                                
                                Switch(config)#
                                
                                

                                This example shows the banner that appears from the previous configuration:

                                Unix> telnet 192.0.2.15
                                
                                Trying 192.0.2.15...
                                
                                Connected to 192.0.2.15.
                                
                                Escape character is '^]'.
                                
                                This is a secure site. Only authorized users are allowed.
                                
                                For access, contact technical support.
                                
                                User Access Verification
                                
                                Password:
                                
                                

                                Example: Configuring a Login Banner

                                This example shows how to configure a login banner by using the dollar sign ($) symbol as the beginning and ending delimiter:

                                Switch(config)# banner login $
                                
                                Access for authorized users only. Please enter your username and password.
                                
                                $
                                
                                Switch(config)#
                                
                                
                                Related References

                                Example: Configuring MAC Address Change Notification Traps

                                This example shows how to specify 172.20.10.10 as the NMS, enable MAC address notification traps to the NMS, enable the MAC address-change notification feature, set the interval time to 123 seconds, set the history-size to 100 entries, and enable traps whenever a MAC address is added on the specified port:

                                Switch(config)# snmp-server host 172.20.10.10 traps private mac-notification
                                Switch(config)# snmp-server enable traps mac-notification change
                                Switch(config)# mac address-table notification change 
                                Switch(config)# mac address-table notification change interval 123
                                Switch(config)# mac address-table notification change history-size 100
                                Switch(config)# interface gigabitethernet1/2/1
                                Switch(config-if)# snmp trap mac-notification change added
                                
                                

                                Example: Configuring MAC Threshold Notification Traps

                                This example shows how to specify 172.20.10.10 as the NMS, enable the MAC address threshold notification feature, set the interval time to 123 seconds, and set the limit to 78 per cent:

                                Switch(config)# snmp-server host 172.20.10.10 traps private mac-notification
                                Switch(config)# snmp-server enable traps mac-notification threshold
                                Switch(config)# mac address-table notification threshold
                                Switch(config)# mac address-table notification threshold interval 123
                                Switch(config)# mac address-table notification threshold limit 78
                                
                                

                                Example: Adding the Static Address to the MAC Address Table

                                This example shows how to add the static address c2f3.220a.12f4 to the MAC address table. When a packet is received in VLAN 4 with this MAC address as its destination address, the packet is forwarded to the specified port:

                                Switch(config)# mac address-table static c2f3.220a.12f4 vlan 4 interface gigabitethernet1/1/1

                                Example: Configuring Unicast MAC Address Filtering

                                This example shows how to enable unicast MAC address filtering and how to configure drop packets that have a source or destination address of c2f3.220a.12f4. When a packet is received in VLAN 4 with this MAC address as its source or destination, the packet is dropped:

                                Switch(config)# mac address-table static c2f3.220a.12f4 vlan 4 drop
                                
                                

                                Additional References for Switch Administration

                                Related Documents

                                Related Topic Document Title

                                System management commands

                                Network management configuration

                                Layer 2 configuration

                                VLAN configuration

                                Standards and RFCs

                                Standard/RFC Title
                                None

                                MIBs

                                MIB MIBs Link

                                All supported MIBs for this release.

                                To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL:

                                http:/​/​www.cisco.com/​go/​mibs

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