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Table Of Contents
Managing the System Time and Date
Understanding the System Clock
Understanding Network Time Protocol
Configuring NTP Authentication
Configuring NTP Broadcast Service
Configuring NTP Access Restrictions
Configuring the Source IP Address for NTP Packets
Displaying the NTP Configuration
Configuring Time and Date Manually
Displaying the Time and Date Configuration
Configuring Summer Time (Daylight Saving Time)
Configuring a System Name and Prompt
Default System Name and Prompt Configuration
Displaying the DNS Configuration
Configuring a Message-of-the-Day Login Banner
Managing the MAC Address Table
Default MAC Address Table Configuration
Changing the Address Aging Time
Removing Dynamic Address Entries
Configuring MAC Address Change Notification Traps
Configuring MAC Address Move Notification Traps
Configuring MAC Threshold Notification Traps
Configuring MAC Limiting per VFI and BD
Adding and Removing Static Address Entries
Configuring Unicast MAC Address Filtering
Disabling MAC Address Learning on a VLAN
Displaying Address Table Entries
Administering the Switch
This chapter describes how to perform one-time operations to administer the Cisco ME 3800X and 3600X switch.
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Managing the System Time and Date
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Managing the System Time and Date
You can manage the system time and date on your switch using automatic configuration, such as the Network Time Protocol (NTP), or manual configuration methods.
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http://www.cisco.com/en/US/docs/ios-xml/ios/fundamentals/command/Cisco_IOS_Configuration_Fundamentals_Command_Reference.html
These sections contain this configuration information:
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Understanding the System Clock
The heart 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:
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The system clock can provide time to these services:
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The system clock keeps track of time internally based on Universal Time Coordinated (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.
Understanding 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.
Figure 5-1 shows a typical network example using NTP. Switch A is the NTP master, with Switches 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 switches, Switch B and Switch F.
Figure 5-1 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.
Configuring NTP
The switch does not have a hardware-supported clock and cannot function as an NTP master clock to which peers synchronize themselves when an external NTP source is not available. The switch also has no hardware support for a calendar. As a result, the ntp update-calendar and the ntp master global configuration commands are not available.
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Default NTP Configuration
NTP is enabled on all interfaces by default. All interfaces receive NTP packets.
Configuring NTP Authentication
This procedure must be coordinated with the administrator of the NTP server; the information you configure in this procedure must be matched by the servers used by the switch to synchronize its time to the NTP server.
Beginning in privileged EXEC mode, follow these steps to authenticate the associations (communications between devices running NTP that provide for accurate timekeeping) with other devices for security purposes:
To disable NTP authentication, use the no ntp authenticate global configuration command. To remove an authentication key, use the no ntp authentication-key number global configuration command. To disable authentication of the identity of a device, use the no ntp trusted-key key-number global configuration command.
This example shows how to configure the switch to synchronize only to devices providing authentication key 42 in the device's NTP packets:
Switch(config)# ntp authenticateSwitch(config)# ntp authentication-key 42 md5 aNiceKeySwitch(config)# ntp trusted-key 42Configuring NTP Associations
An NTP association can be a peer association (this switch can either synchronize to the other device or allow the other device to synchronize to it), or it can be a server association (meaning that only this switch synchronizes to the other device, and not the other way around).
Beginning in privileged EXEC mode, follow these steps to form an NTP association with another device:
You need to configure only one end of an association; the other device can automatically establish the association. If you are using the default NTP version (Version 3) and NTP synchronization does not occur, try using NTP Version 2. Many NTP servers on the Internet run Version 2.
To remove a peer or server association, use the no ntp peer ip-address or the no ntp server ip-address global configuration command.
This example shows how to configure the switch to synchronize its system clock with the clock of the peer at IP address 172.16.22.44 using NTP Version 2:
Switch(config)# ntp server 172.16.22.44 version 2Configuring NTP Broadcast Service
The communications between devices running NTP (known as associations) are usually statically configured; each device is given the IP addresses 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, the information flow is one-way only.
The switch can send or receive NTP broadcast packets on an interface-by-interface basis if there is an NTP broadcast server, such as a router, broadcasting time information on the network. The switch can send NTP broadcast packets to a peer so that the peer can synchronize to it. The switch can also receive NTP broadcast packets to synchronize its own clock. This section provides procedures for both sending and receiving NTP broadcast packets.
Beginning in privileged EXEC mode, follow these steps to configure the switch to send NTP broadcast packets to peers so that they can synchronize their clock to the switch:
To disable the interface from sending NTP broadcast packets, use the no ntp broadcast interface configuration command.
This example shows how to configure a port to send NTP Version 2 packets:
Switch(config)# interface gigabitethernet0/1Switch(config-if)# ntp broadcast version 2Beginning in privileged EXEC mode, follow these steps to configure the switch to receive NTP broadcast packets from connected peers:
To disable an interface from receiving NTP broadcast packets, use the no ntp broadcast client interface configuration command. To change the estimated round-trip delay to the default, use the no ntp broadcastdelay global configuration command.
This example shows how to configure a port to receive NTP broadcast packets:
Switch(config)# interface gigabitethernet0/1Switch(config-if)# ntp broadcast clientConfiguring NTP Access Restrictions
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Creating an Access Group and Assigning a Basic IP Access List
Beginning in privileged EXEC mode, follow these steps to control access to NTP services by using access lists:
The access group keywords are scanned in this order, from least restrictive to most restrictive:
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If the source IP address matches the access lists for more than one access type, the first type is granted. If no access groups are specified, all access types are granted to all devices. If any access groups are specified, only the specified access types are granted.
To remove access control to the switch NTP services, use the no ntp access-group {query-only | serve-only | serve | peer} global configuration command.
This example shows how to configure the switch to allow itself to synchronize to a peer from access list 99. However, the switch restricts access to allow only time requests from access list 42:
Switch# configure terminalSwitch(config)# ntp access-group peer 99Switch(config)# ntp access-group serve-only 42Switch(config)# access-list 99 permit 172.20.130.5Switch(config)# access list 42 permit 172.20.130.6Disabling NTP Services on a Specific Interface
NTP services are enabled on all interfaces by default.
Beginning in privileged EXEC mode, follow these steps to disable NTP packets from being received on an interface:
To re-enable receipt of NTP packets on an interface, use the no ntp disable interface configuration command.
Configuring the Source IP Address for NTP Packets
When the switch sends an NTP packet, the source IP address is normally set to the address of the interface through which the NTP packet is sent. Use the ntp source global configuration command when you want to use a particular source IP address for all NTP packets. The address is taken from the specified interface. This command is useful if the address on an interface cannot be used as the destination for reply packets.
Beginning in privileged EXEC mode, follow these steps to configure a specific interface from which the IP source address is to be taken:
The specified interface is used for the source address for all packets sent to all destinations. If a source address is to be used for a specific association, use the source keyword in the ntp peer or ntp server global configuration command as described in the "Configuring NTP Associations" section.
Displaying the NTP Configuration
You can use two privileged EXEC commands to display NTP information:
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For detailed information about the fields in these displays, see the Cisco IOS Configuration Fundamentals Command Reference, Release 12.2.
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.
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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.
Beginning in privileged EXEC mode, follow these steps to set the system clock:
This example shows how to manually set the system clock to 1:32 p.m. on July 23, 2001:
Switch# clock set 13:32:00 23 July 2001Displaying 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:
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Configuring the Time Zone
Beginning in privileged EXEC mode, follow these steps to manually configure the time zone:
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.
Configuring Summer Time (Daylight Saving Time)
Beginning in privileged EXEC mode, follow these steps to configure summer time (daylight saving time) in areas where it starts and ends on a particular day of the week each year:
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.
This example shows how to specify that summer time starts on the first Sunday in April at 02:00 and ends on the last Sunday in October at 02:00:
Switch(config)# clock summer-time PDT recurring 1 Sunday April 2:00 last Sunday October 2:00Beginning in privileged EXEC mode, 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):
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.
This example shows how to set summer time to start on October 12, 2000, at 02:00, and end on April 26, 2001, at 02:00:
Switch(config)# clock summer-time pdt date 12 October 2000 2:00 26 April 2001 2:00Configuring a 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, refer to the Cisco IOS Configuration Fundamentals Command Reference and the Cisco IOS IP Routing Command References.
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Default System Name and Prompt Configuration
The default switch system name and prompt is Switch.
Configuring a System Name
Beginning in privileged EXEC mode, follow these steps to manually configure a system name:
When you set the system name, it is also used as the system prompt.
To return to the default hostname, use the no hostname global configuration command.
Understanding 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.
These sections contain this configuration information:
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Default DNS Configuration
Table 5-2 Default DNS Configuration
DNS enable state
Enabled.
DNS default domain name
None configured.
DNS servers
No name server addresses are configured.
Setting Up DNS
Beginning in privileged EXEC mode, follow these steps to set up your switch to use the 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.
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.
Displaying the DNS Configuration
To display the DNS configuration information, use the show running-config privileged EXEC command.
Creating a Banner
You can configure a message-of-the-day (MOTD) and a login banner. The MOTD banner displays 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 also displays on all connected terminals. It appears after the MOTD banner and before the login prompts.
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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.
Beginning in privileged EXEC mode, follow these steps to configure a MOTD login banner:
To delete the MOTD banner, use the no banner motd global configuration command.
This example shows how to configure a MOTD banner for the switch 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 172.2.5.4Trying 172.2.5.4...Connected to 172.2.5.4.Escape character is '^]'.This is a secure site. Only authorized users are allowed.For access, contact technical support.User Access VerificationPassword: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.
Beginning in privileged EXEC mode, follow these steps to configure a login banner:
To delete the login banner, use the no banner login global configuration command.
This example shows how to configure a login banner for the switch 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)#Managing the 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:
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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).
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Building the Address Table
With multiple MAC addresses supported on all ports, you can connect any port on the switch to individual workstations, repeaters, switches, routers, or 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 stations 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 1, 9, and 10 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.
You can disable MAC address learning on a per-VLAN basis. Customers in a service provider network can tunnel a large number of MAC addresses through the network and fill up the available MAC address table space. You can control MAC address learning on a VLAN and manage the MAC address table space that is available on the switch 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. See the "Disabling MAC Address Learning on a VLAN" section for more information.
Default MAC Address Table Configuration
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.
Beginning in privileged EXEC mode, follow these steps to configure the dynamic address table aging time:
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.
Beginning in privileged EXEC mode, follow these steps to configure the switch to send MAC address change notification traps to an NMS host:
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.
This example shows how to specify 172.20.10.10 as the NMS, enable the switch to send 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-notificationSwitch(config)# snmp-server enable traps mac-notification changeSwitch(config)# mac address-table notification changeSwitch(config)# mac address-table notification change interval 123Switch(config)# mac address-table notification change history-size 100Switch(config)# interface gigabitethernet0/2Switch(config-if)# snmp trap mac-notification change addedYou 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.
Beginning in privileged EXEC mode, follow these steps to configure the switch to send MAC address-move notification traps to an NMS host:
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.
This example shows how to specify 172.20.10.10 as the NMS, enable the switch to send MAC address move notification traps to the NMS, enable the MAC address move notification feature, and enable traps when a MAC address moves from one port to another.
Switch(config)# snmp-server host 172.20.10.10 traps private mac-notificationSwitch(config)# snmp-server enable traps mac-notification moveSwitch(config)# mac address-table notification mac-moveYou 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.
Beginning in privileged EXEC mode, follow these steps to configure the switch to send MAC address table threshold notification traps to an NMS host:
To disable MAC address-threshold notification traps, use the no snmp-server enable traps mac-notification threshold global configuration command. To disable the MAC address-threshold notification feature, use the no mac address-table notification threshold global configuration command.
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-notificationSwitch(config)# snmp-server enable traps mac-notification thresholdSwitch(config)# mac address-table notification thresholdSwitch(config)# mac address-table notification threshold interval 123Switch(config)# mac address-table notification threshold limit 78You can verify your settings by entering the show mac address-table notification threshold privileged EXEC commands.
Configuring MAC Limiting per VFI and BD
Mac Limiting per VFI and BD feature restricts the total number of mac addresses learned globally under a particular bridge domain or VLAN.
Mac address limiting per VLAN restricts the number of macs being learnt per VLAN or BD on an EFP, pseudowire or switchport to a specified number.
When the total number mac addresses learnt on a vlan exceeds the maximum permitted value a violation action is taken, to restrict further learning or inform the user through an error message to take further action.
When a violation occurs the following options are available:
Warning:
Specifies that one syslog message will be sent and no further action will be taken when the action is violated. One syslog message is sent when the mac count exceeds the configured limit (Exceed notification) and no more syslog message for the vlan unless the violation is no longer valid (Drop notification). However further learning of new macs and forwarding of traffic continues despite the violation
Limit:
Specifies that the one syslog message will be sent and/or a corresponding trap will be generated with the MAC limit when the action is violated. MAC learning on the vlan is disabled when violation occurs. No new macs are learnt on the vlan until the recovery mechanism activates. However even though new macs are not learned, frames are still flooded in the system. To stop flooding use the flood keyword.
Flood:
This sub action allows the user to disable unknown unicast flooding on a given VLAN. This option is only available when the limit keyword is configured. Unknown unicast flooding is disabled only for the interval necessary to limit the entries. This improves the performance and flooding will be reenabled when the total number of mac entries is dropped to threshold value.
Shutdown:
Specifies that the one syslog message will be sent and/or the VLAN is moved to the blocked state when the action is violated.
Therefore all learning and forwarding of traffic is halted on the VLAN. The VLAN remains in this state until it is re-enabled through CLI.
There is a recovery mechanism that activates in the case of action limit. When the total mac count drops equal to or below the threshold value, the recovery mechanism activates. The threshold value is dependent on the maximum limit configured on vlan (80% of the limit value). The recovery mechanism will reverts the action taken during violation. For e.g if learning was disabled as a violation action then it will be re-enabled.
Beginning in privileged EXEC mode, follow these steps to configure mac limiting per VLAN or BD:
This example shows how to enable per-VLAN MAC limiting. The first instance of the mac-address-table limit command enables MAC limiting. The second instance of the command sets the limit and any optional actions to be imposed at the VLAN level.
Switch# enableSwitch# configure terminalSwitch(config)# mac-address-table limitSwitch(config)# mac-address-table limit vlan 10 maximum 100 action limit floodSwitch(config)# endSwitch# show mac-address-table limit vlan 10vlan module action maximum Total entries-------+---------+-----------+--------+----------------10 1 limit 100 0Adding and Removing Static Address Entries
A static address has these characteristics:
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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.
Beginning in privileged EXEC mode, follow these steps to add a static address:
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.
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 gigabitethernet0/1Configuring Unicast MAC Address Filtering
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:
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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.
Beginning in privileged EXEC mode, follow these steps to configure the switch to drop a source or destination unicast static address:
To disable unicast MAC address filtering, use the no mac address-table static mac-addr vlan vlan-id global configuration command.
This example shows how to enable unicast MAC address filtering and to configure the switch to 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 dropDisabling MAC Address Learning on a VLAN
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:
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Beginning in privileged EXEC mode, follow these steps to disable MAC address learning on a VLAN:
To reenable MAC address learning on a VLAN or bridge, use the default mac address-table learning {vlan vlan-id | bridge-domain domain-id} global configuration command. You can also reenable MAC address learning on a VLAN by entering the mac address-table learning {vlan vlan-id | bridge-domain domain-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-config command. The second command causes the configuration to appear in the show running-config privileged EXEC command display.
This example shows how to disable MAC address learning on VLAN 200:
Switch(config)# no mac address-table learning vlan 200You can display the MAC address learning status of all VLANs or a specified VLAN by entering the show mac-address-table learning 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 Table 5-4:
Managing the ARP Table
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 15.x documentation on Cisco.com.
