Catalyst 3750 Switch Software Configuration Guide, 12.2(25)SE

Configuring Port-Based Traffic Control

This chapter describes how to configure the port-based traffic control features on the Catalyst 3750 switch. Unless otherwise noted, the term switch refers to a standalone switch and a switch stack.

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

This chapter consists of these sections:

•Configuring Storm Control

•Configuring Protected Ports

•Configuring Port Blocking

•Configuring Port Security

•Displaying Port-Based Traffic Control Settings

Configuring Storm Control

These sections include storm control configuration information and procedures:

•Understanding Storm Control

•Default Storm Control Configuration

•Configuring Storm Control and Threshold Levels

Understanding Storm Control

Storm control prevents traffic on a LAN from being disrupted by a broadcast, multicast, or unicast storm on one of the physical interfaces. A LAN storm occurs when packets flood the LAN, creating excessive traffic and degrading network performance. Errors in the protocol-stack implementation or in the network configuration can cause a storm.

Storm control (or traffic suppression) monitors packets passing from an interface to the switching bus and determines if the packet is unicast, multicast, or broadcast. The switch counts the number of packets of a specified type received within the 1-second time interval and compares the measurement with a predefined suppression-level threshold.

Storm control uses one of these methods to measure traffic activity:

•Bandwidth as a percentage of the total available bandwidth of the port that can be used by the broadcast, multicast, or unicast traffic

•Traffic rate in packets per second at which broadcast, multicast, or unicast packets are received (Cisco IOS Release 12.2(25)SE or later)

•Traffic rate in bits per second at which broadcast, multicast, or unicast packets are received (Cisco IOS Release 12.2(25)SE or later)

With each method, the port blocks traffic when the rising threshold is reached. The port remains blocked until the traffic rate drops below the falling threshold (if one is specified) and then resumes normal forwarding. If the falling suppression level is not specified, the switch blocks all traffic until the traffic rate drops below the rising suppression level. In general, the higher the level, the less effective the protection against broadcast storms.

Note When the storm control threshold for multicast traffic is reached, all multicast traffic except control traffic, such as bridge protocol data unit (BDPU) and Cisco Discovery Protocol (CDP) frames, are blocked. However, the switch does not differentiate between routing updates, such as OSPF, and regular multicast data traffic, so both types of traffic are blocked.

The graph in Figure 24-1 shows broadcast traffic patterns on an interface over a given period of time. The example can also be applied to multicast and unicast traffic. In this example, the broadcast traffic being forwarded exceeded the configured threshold between time intervals T1 and T2 and between T4 and T5. When the amount of specified traffic exceeds the threshold, all traffic of that kind is dropped for the next time period. Therefore, broadcast traffic is blocked during the intervals following T2 and T5. At the next time interval (for example, T3), if broadcast traffic does not exceed the threshold, it is again forwarded.

Figure 24-1 Broadcast Storm Control Example

The combination of the storm-control suppression level and the 200-millisecond time interval control the way the storm control algorithm works. A higher threshold allows more packets to pass through. A threshold value of 100 percent means that no limit is placed on the traffic. A value of 0.0 means that all broadcast, multicast, or unicast traffic on that port is blocked.

The combination of the storm-control suppression level and the 1-second time interval control the way the storm control algorithm works. A higher threshold allows more packets to pass through.

Note Because packets do not arrive at uniform intervals, the 1-second time interval during which traffic activity is measured can affect the behavior of storm control.

You use the storm-control interface configuration commands to set the threshold value for each traffic type.

Default Storm Control Configuration

By default, unicast, broadcast, and multicast storm control are disabled on the switch interfaces; that is, the suppression level is 100 percent.

Configuring Storm Control and Threshold Levels

You configure storm control on a port and enter the threshold level that you want to be used by a particular type of traffic.

However, because of hardware limitations and the way in which packets of different sizes are counted, threshold percentages are approximations. Depending on the sizes of the packets making up the incoming traffic, the actual enforced threshold might differ from the configured level by several percentage points.

Note Storm control is supported only on physical interfaces; it is not supported on EtherChannel port-channels or physical interfaces that are members of port channels even though the command is available in the CLI. If a physical interface with storm control configured joins an EtherChannel, the storm control configuration for the physical interface is removed from the running configuration.

Beginning in privileged EXEC mode, follow these steps to storm control and threshold levels:

To disable storm control, use the no storm-control {broadcast | multicast | unicast} level interface configuration command.

This example shows how to enable unicast storm control on a port with an 87-percent rising suppression level and a 65-percent falling suppression level:

Switch# configure terminal

Switch(config)# interface gigabitethernet1/0/1

Switch(config-if)# storm-control unicast level 87 65

Configuring Protected Ports

Some applications require that no traffic be forwarded at Layer 2 between ports on the same switch so that one neighbor does not see the traffic generated by another neighbor. In such an environment, the use of protected ports ensures that there is no exchange of unicast, broadcast, or multicast traffic between these ports on the switch.

Protected ports have these features:

•A protected port does not forward any traffic (unicast, multicast, or broadcast) to any other port that is also a protected port. Data traffic cannot be forwarded between protected ports at Layer 2; only control traffic, such as PIM packets, is forwarded because these packets are processed by the CPU and forwarded in software. All data traffic passing between protected ports must be forwarded through a Layer 3 device.

•Forwarding behavior between a protected port and a nonprotected port proceeds as usual.

Because a switch stack represents a single logical switch, Layer 2 traffic is not forwarded between any protected ports in the switch stack, whether they are on the same or different switches in the stack.

Default Protected Port Configuration

The default is to have no protected ports defined.

Protected Port Configuration Guidelines

You can configure protected ports on a physical interface (for example, Gigabit Ethernet port 1) or an EtherChannel group (for example, port-channel 5). When you enable protected ports for a port channel, it is enabled for all ports in the port-channel group.

Do not configure a private-VLAN port as a protected port. Do not configure a protected port as a private-VLAN port. A private-VLAN isolated port does not forward traffic to other isolated ports or community ports. For more information about private VLANs, see "Configuring Private VLANs."

Configuring a Protected Port

Beginning in privileged EXEC mode, follow these steps to define a port as a protected port:

To disable protected port, use the no switchport protected interface configuration command.

This example shows how to configure a port as a protected port:

Switch# configure terminal

Switch(config)# interface gigabitethernet1/0/1

Switch(config-if)# switchport protected

Switch(config-if)# end

Configuring Port Blocking

By default, the switch floods packets with unknown destination MAC addresses out of all ports. If unknown unicast and multicast traffic is forwarded to a protected port, there could be security issues. To prevent unknown unicast or multicast traffic from being forwarded from one port to another, you can block a port (protected or nonprotected) from flooding unknown unicast or multicast packets to other ports.

Default Port Blocking Configuration

The default is to not block flooding of unknown multicast and unicast traffic out of a port, but to flood these packets to all ports.

Blocking Flooded Traffic on an Interface

Note The interface can be a physical interface or an EtherChannel group. When you block multicast or unicast traffic for a port channel, it is blocked on all ports in the port-channel group.

Beginning in privileged EXEC mode, follow these steps to disable the flooding of multicast and unicast packets out of an interface:

To return the interface to the default condition where no traffic is blocked and normal forwarding occurs on the port, use the no switchport block {multicast | unicast} interface configuration commands.

This example shows how to block unicast and multicast flooding on a port:

Switch# configure terminal

Switch(config)# interface gigabitethernet1/0/1

Switch(config-if)# switchport block multicast

Switch(config-if)# switchport block unicast

Switch(config-if)# end

Configuring Port Security

You can use the port security feature to restrict input to an interface by limiting and identifying MAC addresses of the stations allowed to access the port. When you assign secure MAC addresses to a secure port, the port does not forward packets with source addresses outside the group of defined addresses. If you limit the number of secure MAC addresses to one and assign a single secure MAC address, the workstation attached to that port is assured the full bandwidth of the port.

If a port is configured as a secure port and the maximum number of secure MAC addresses is reached, when the MAC address of a station attempting to access the port is different from any of the identified secure MAC addresses, a security violation occurs. Also, if a station with a secure MAC address configured or learned on one secure port attempts to access another secure port, a violation is flagged.

These sections include port security configuration information and procedures:

•Understanding Port Security

•Default Port Security Configuration

•Configuration Guidelines

•Enabling and Configuring Port Security

•Enabling and Configuring Port Security Aging

•Port Security and Switch Stacks

Understanding Port Security

This section contains information about these topics:

•Secure MAC Addresses

•Security Violations

Secure MAC Addresses

You configure the maximum number of secure addresses allowed on a port by using the switchport port-security maximum value interface configuration command.

Note If you try to set the maximum value to a number less than the number of secure addresses already configured on an interface, the command is rejected.

The switch supports these types of secure MAC addresses:

•Static secure MAC addresses—These are manually configured by using the switchport port-security mac-address mac-address interface configuration command, stored in the address table, and added to the switch running configuration.

•Dynamic secure MAC addresses—These are dynamically configured, stored only in the address table, and removed when the switch restarts.

•Sticky secure MAC addresses—These can be dynamically learned or manually configured, stored in the address table, and added to the running configuration. If these addresses are saved in the configuration file, when the switch restarts, the interface does not need to dynamically reconfigure them.

You can configure an interface to convert the dynamic MAC addresses to sticky secure MAC addresses and to add them to the running configuration by enabling sticky learning. To enable sticky learning, enter the switchport port-security mac-address sticky interface configuration command. When you enter this command, the interface converts all the dynamic secure MAC addresses, including those that were dynamically learned before sticky learning was enabled, to sticky secure MAC addresses. All sticky secure MAC addresses are added to the running configuration.

The sticky secure MAC addresses do not automatically become part of the configuration file, which is the startup configuration used each time the switch restarts. If you save the sticky secure MAC addresses in the configuration file, when the switch restarts, the interface does not need to relearn these addresses. If you do not save the sticky secure addresses, they are lost.

If sticky learning is disabled, the sticky secure MAC addresses are converted to dynamic secure addresses and are removed from the running configuration.

The maximum number of secure MAC addresses that you can configure on a switch stack is set by the maximum number of available MAC addresses allowed in the system. This number is determined by the active Switch Database Management (SDM) template. See "Configuring SDM Templates." This number is the total of available MAC addresses, including those used for other Layer 2 functions and any other secure MAC addresses configured on interfaces.

Security Violations

It is a security violation when one of these situations occurs:

•The maximum number of secure MAC addresses have been added to the address table, and a station whose MAC address is not in the address table attempts to access the interface.

•An address learned or configured on one secure interface is seen on another secure interface in the same VLAN.

You can configure the interface for one of three violation modes, based on the action to be taken if a violation occurs:

•protect—when the number of secure MAC addresses reaches the maximum limit allowed on the port, packets with unknown source addresses are dropped until you remove a sufficient number of secure MAC addresses to drop below the maximum value or increase the number of maximum allowable addresses. You are not notified that a security violation has occurred.

Note We do not recommend configuring the protect violation mode on a trunk port. The protect mode disables learning when any VLAN reaches its maximum limit, even if the port has not reached its maximum limit.

•restrict—when the number of secure MAC addresses reaches the maximum limit allowed on the port, packets with unknown source addresses are dropped until you remove a sufficient number of secure MAC addresses to drop below the maximum value or increase the number of maximum allowable addresses. In this mode, you are notified that a security violation has occurred. An SNMP trap is sent, a syslog message is logged, and the violation counter increments.

•shutdown—a port security violation causes the interface to become error-disabled and to shut down immediately, and the port LED turns off. An SNMP trap is sent, a syslog message is logged, and the violation counter increments. When a secure port is in the error-disabled state, you can bring it out of this state by entering the errdisable recovery cause psecure-violation global configuration command, or you can manually re-enable it by entering the shutdown and no shut down interface configuration commands. This is the default mode.

Table 24-1 shows the violation mode and the actions taken when you configure an interface for port security.

Default Port Security Configuration

Table 24-2 shows the default port security configuration for an interface.

Configuration Guidelines

Follow these guidelines when configuring port security:

•Port security can only be configured on static access ports or trunk ports. A secure port cannot be a dynamic access port.

•A secure port cannot be a destination port for Switched Port Analyzer (SPAN).

•A secure port cannot belong to a Fast EtherChannel or a Gigabit EtherChannel port group.

•You cannot configure static secure or sticky secure MAC addresses in the voice VLAN.

Note Voice VLAN is only supported on access ports and not on trunk ports, even though the configuration is allowed.

•A secure port cannot be a private-VLAN port.

•When you enable port security on an interface that is also configured with a voice VLAN, you must set the maximum allowed secure addresses on the port to two plus the maximum number of secure addresses allowed on the access VLAN. When the port is connected to a Cisco IP phone, the IP phone requires up to two MAC addresses. The IP phone address is learned on the voice VLAN and might also be learned on the access VLAN. Connecting a PC to the IP phone requires additional MAC addresses.

•If any type of port security is enabled on the access VLAN, dynamic port security is automatically enabled on the voice VLAN. You cannot configure port security on a per-VLAN basis.

•When a voice VLAN is configured on a secure port that is also configured as a sticky secure port, all addresses on the voice VLAN are learned as dynamic secure addresses, and all addresses seen on the access VLAN to which the port belongs are learned as sticky secure addresses.

•When you enter a maximum secure address value for an interface, and the new value is greater than the previous value, the new value overwrites the previously configured value. If the new value is less than the previous value and the number of configured secure addresses on the interface exceeds the new value, the command is rejected.

•The switch does not support port security aging of sticky secure MAC addresses.

Table 24-3 summarizes port security compatibility with other port-based features.

Enabling and Configuring Port Security

Beginning in privileged EXEC mode, follow these steps to restrict input to an interface by limiting and identifying MAC addresses of the stations allowed to access the port:

To return the interface to the default condition as not a secure port, use the no switchport port-security interface configuration command. If you enter this command when sticky learning is enabled, the sticky secure addresses remain part of the running configuration but are removed from the address table. All addresses are now dynamically learned.

To return the interface to the default number of secure MAC addresses, use the no switchport port-security maximum value interface configuration command. To return the violation mode to the default condition (shutdown mode), use the no switchport port-security violation {protocol | restrict} interface configuration command.

To disable sticky learning on an interface, use the no switchport port-security mac-address sticky interface configuration command. The interface converts the sticky secure MAC addresses to dynamic secure addresses. However, if you have previously saved the configuration with the sticky MAC addresses, you should save the configuration again after entering the no switchport port-security mac-address sticky command, or the sticky addresses will be restored if the switch reboots.

To delete a specific secure MAC address from the address table, use the no switchport port-security mac-address mac-address interface configuration command.

To delete all dynamic secure addresses on an interface from the address table, enter the no switchport port-security interface configuration command followed by the switchport port-security command (to re-enable port security on the interface). If you use the no switchport port-security mac-address sticky interface configuration command to convert sticky secure MAC addresses to dynamic secure MAC addresses before entering the no switchport port-security command, all secure addresses on the interface except those that were manually configured are deleted.

You must specifically delete configured secure MAC addresses from the address table by using the no switchport port-security mac-address mac-address interface configuration command.

This example shows how to enable port security on a port and to set the maximum number of secure addresses to 50. The violation mode is the default, no static secure MAC addresses are configured, and sticky learning is enabled.

Switch(config)# interface gigabitethernet1/0/1

Switch(config-if)# switchport mode access

Switch(config-if)# switchport port-security

Switch(config-if)# switchport port-security maximum 50

Switch(config-if)# switchport port-security mac-address sticky

This example shows how to configure a static secure MAC address on VLAN 3 on a port:

Switch(config)# interface gigabitethernet1/0/2

Switch(config-if)# switchport mode trunk

Switch(config-if)# switchport port-security

Switch(config-if)# switchport port-security mac-address 0000.02000.0004 vlan 3

Enabling and Configuring Port Security Aging

You can use port security aging to set the aging time for all secure addresses on a port. Two types of aging are supported per port:

•Absolute—The secure addresses on the port are deleted after the specified aging time.

•Inactivity—The secure addresses on the port are deleted only if the secure addresses are inactive for the specified aging time.

Use this feature to remove and add devices on a secure port without manually deleting the existing secure MAC addresses and to still limit the number of secure addresses on a port. You can enable or disable the aging of secure addresses on a per-port basis.

Beginning in privileged EXEC mode, follow these steps to configure port security aging:

To disable port security aging for all secure addresses on a port, use the no switchport port-security aging time interface configuration command. To disable aging for only statically configured secure addresses, use the no switchport port-security aging static interface configuration command.

This example shows how to set the aging time as 2 hours for the secure addresses on a port:

Switch(config)# interface gigabitethernet1/0/1 

Switch(config-if)# switchport port-security aging time 120

This example shows how to set the aging time as 2 minutes for the inactivity aging type with aging enabled for the configured secure addresses on the interface:

Switch(config-if)# switchport port-security aging time 2 

Switch(config-if)# switchport port-security aging type inactivity 

Switch(config-if)# switchport port-security aging static

You can verify the previous commands by entering the show port-security interface interface-id privileged EXEC command.

Port Security and Switch Stacks

When a switch joins a stack, the new switch will get the configured secure addresses. All dynamic secure addresses are downloaded by the new stack member from the other stack members.

When a switch (either the stack master or a stack member) leaves the stack, the remaining stack members are notified, and the secure MAC addresses configured or learned by that switch are deleted from the secure MAC address table. For more information about switch stacks, see "Managing Switch Stacks."

Displaying Port-Based Traffic Control Settings

The show interfaces interface-id switchport privileged EXEC command displays (among other characteristics) the interface traffic suppression and control configuration. The show storm-control and show port-security privileged EXEC commands display storm control and port security settings.

To display traffic control information, use one or more of the privileged EXEC commands in Table 24-4.