Cisco ME3400E Ethernet Access Switch Software Configuration Guide, Rel 12.2(60)EZ

Supported VLANs

VLANs are identified with a number from 1 to 4094. VLAN IDs 1002 through 1005 are reserved for Token Ring and FDDI VLANs. VLAN IDs greater than 1005 are extended-range VLANs and are not stored in the VLAN database.

Although the switch supports a total of 1005 (normal-range and extended-range) VLANs, the number of routed ports, SVIs, and other configured features affects the use of the switch hardware.

The switch supports per-VLAN spanning-tree plus (PVST+) or rapid PVST+ with a maximum of 128 spanning-tree instances. One spanning-tree instance is allowed per VLAN.

Note Network node interfaces (NNIs) support STP by default. Enhanced network interfaces (ENIs) can be configured to support STP. User network interfaces (UNIs) do not support STP and by default are always in a forwarding state.

See the “VLAN Configuration Guidelines” section for more information about the number of spanning-tree instances and the number of VLANs. The switch supports IEEE 802.1Q trunking for sending VLAN traffic over Ethernet ports.

Normal-Range VLANs

Normal-range VLANs are VLANs with VLAN IDs 1 to 1005. You can add, modify or remove configurations for VLANs 2 to 1001 in the VLAN database. (VLAN IDs 1 and 1002 to 1005 are automatically created and cannot be removed.)

Configurations for VLAN IDs 1 to 1005 are written to the file vlan.dat (VLAN database), and you can display them by entering the show vlan privileged EXEC command. The vlan.dat file is stored in flash memory.

Caution You can cause inconsistency in the VLAN database if you try to manually delete the vlan.dat file. If you want to modify the VLAN configuration, use the commands described in these sections and in the command reference for this release.

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You can set these parameters when you create a new normal-range VLAN or modify an existing VLAN in the VLAN database:

• VLAN ID
• VLAN name
• VLAN type (Ethernet, Fiber Distributed Data Interface [FDDI], FDDI network entity title [NET], TrBRF, or TrCRF, Token Ring, Token Ring-Net)

Note The switch supports only Ethernet VLANs. You can configure parameters for FDDI and Token Ring VLANs and view the results in the vlan.dat file, but these parameters are not used.

• VLAN state (active or suspended)
• Maximum transmission unit (MTU) for the VLAN
• Security Association Identifier (SAID)
• Bridge identification number for TrBRF VLANs
• Ring number for FDDI and TrCRF VLANs
• Parent VLAN number for TrCRF VLANs
• Spanning Tree Protocol (STP) type for TrCRF VLANs
• VLAN number to use when translating from one VLAN type to another
• Private VLAN. Configure the VLAN as a primary or secondary private VLAN. For information about private VLANs, see Chapter14, “Configuring Private VLANs”
• Remote SPAN VLAN. Configure the VLAN as the Remote Switched Port Analyzer (RSPAN) VLAN for a remote SPAN session. For more information on remote SPAN, see Chapter1, “Configuring SPAN and RSPAN”
• UNI-ENI VLAN configuration

For extended-range VLANs, you can configure only MTU, private VLAN, remote SPAN VLAN, and UNI-ENI VLAN parameters.

Note This chapter does not provide configuration details for most of these parameters. For complete information on the commands and parameters that control VLAN configuration, see the command reference for this release.

Extended-Range VLANs

You can create extended-range VLANs (in the range 1006 to 4094) to enable service providers to extend their infrastructure to a greater number of customers. The extended-range VLAN IDs are allowed for any switchport commands that allow VLAN IDs. Extended-range VLAN configurations are not stored in the VLAN database, but they are stored in the switch running configuration file, and you can save the configuration in the startup configuration file by using the copy running-config startup-config privileged EXEC command.

Note Although the switch supports 4094 VLAN IDs, the actual number of VLANs supported is 1005.

VLAN Port Membership Modes

You configure a port to belong to a VLAN by assigning a membership mode that specifies the kind of traffic that the port carries and the number of VLANs to which it can belong. Table 13-1 lists the membership modes and characteristics.

For more detailed definitions of access and trunk modes and their functions, see Table 13-4.

When a port belongs to a VLAN, the switch learns and manages the addresses associated with the port on a per-VLAN basis. For more information, see the “Managing the MAC Address Table” section.

UNI-ENI VLANs

The Cisco ME switch is the boundary between customer networks and the service-provider network, with user network interfaces (UNIs) and enhanced interface interfaces (ENIs) connected to the customer side of the network. When customer traffic enters or leaves the service-provider network, the customer VLAN ID must be isolated from other customers’ VLAN IDs. You can achieve this isolation by several methods, including using private VLANs. On the Cisco ME switch, this isolation occurs by default by using UNI-ENI VLANs.

There are two types of UNI-ENI VLANs:

• UNI-ENI isolated VLAN—This is the default VLAN state for all VLANs created on the switch. Local switching does not occur among UNIs or ENIs on the switch that belong to the same UNI-ENI isolated VLAN. This configuration is designed for cases when different customers are connected to UNIs or ENIs on the same switch. However, switching is allowed among UNIs or ENIs on different switches even though they belong to the same UNI-ENI isolated VLAN.
• UNI-ENI community VLAN—Local switching is allowed among UNIs and ENIs on the switch that belong to the same community VLAN. If UNIs or ENIs belong to the same customer, and you want to switch packets between the ports, you can configure the common VLAN as a UNI-ENI community VLAN. There is no local switching between the ports in a UNI-ENI community VLAN and ports outside of the VLAN. There is no restriction to the number of UNIs and ENIs that you can add to a community VLAN or private VLAN.

Note Local switching takes place between ENIs and UNIs in the same community VLAN. Because you can enable spanning tree on ENIs, but not on UNIs, you should use caution when configuring ENIs and UNIs in the same community VLAN. UNIs are always in the forwarding state.

Network node interfaces (NNIs) are not affected by the type of UNI-ENI VLAN to which they belong. Switching can occur between NNIs and other NNIs or UNIs or ENIs on the switch or other switches that are part of the same VLAN, regardless of VLAN type.

In the configuration in Figure 13-2, if VLAN 10 is a UNI-ENI isolated VLAN and VLAN 20 is a UNI-ENI community VLAN, local switching does not take place among Fast Ethernet ports 1-4, but local switching can occur between Fast Ethernet ports 6-10. The NNIs in both VLAN 10 and VLAN 20 can exchange packets with the UNIs or ENIs in the same VLAN.

Figure 13-2 UNI -ENI Isolated and Community VLANs in the Cisco ME Switch

A UNI or ENI can be an access port, a trunk port, a private VLAN port, or an IEEE 802.1Q tunnel port. It can also be a member of an EtherChannel.

When a UNI or ENI configured as an IEEE 802.1Q trunk port belongs to a UNI-ENI isolated VLAN, the VLAN on the trunk is isolated from the same VLAN ID on a different trunk port or an access port. Other VLANs on the trunk port can be of different types (private VLAN, UNI-ENI community VLAN, and so on). For example, a UNI access port and one VLAN on a UNI trunk port can belong to the same UNI-ENI isolated VLAN. In this case, isolation occurs between the UNI access port and the VLAN on the UNI trunk port. Other access ports and other VLANs on the trunk port are isolated because they belong to different VLANs.

UNIs, ENIs, and NNIs are always isolated from ports on different VLANs.

Default Ethernet VLAN Configuration

The switch supports only Ethernet interfaces. Table 13-2 shows the default configuration for Ethernet VLANs.

Note On extended-range VLANs, you can change only the MTU size, the private VLAN, the remote SPAN, and the UNI-ENI VLAN configuration. All other characteristics must remain at the default conditions.

VLAN Configuration Guidelines

Follow these guidelines when creating and modifying VLANs in your network:

• The switch supports 1005 VLANs.
• Normal-range Ethernet VLANs are identified with a number between 1 and 1001. VLAN numbers 1002 through 1005 are reserved for Token Ring and FDDI VLANs.
• The switch does not support Token Ring or FDDI media. The switch does not forward FDDI, FDDI-Net, TrCRF, or TrBRF traffic.
• VLAN configurations for VLANs 1 to 1005 are always saved in the VLAN database and in the switch running configuration file.
• Configuration options for VLAN IDs 1006 through 4094 (extended-range VLANs) are limited to MTU, RSPAN VLAN, private VLAN, and UNI-ENI VLAN. Extended-range VLANs are not saved in the VLAN database.
• Spanning Tree Protocol (STP) is enabled by default for only NNIs on all VLANs. You can configure STP on ENIs. NNIs and ENIs in the same VLAN are in the same spanning-tree instance. The switch supports 128 spanning-tree instances. If a switch has more active VLANs than supported spanning-tree instances, spanning tree can be enabled on 128 VLANs and is disabled on the remaining VLANs. If you have already used all available spanning-tree instances on a switch, adding another VLAN creates a VLAN on that switch that is not running spanning tree. If you have the default allowed list on the trunk ports of that switch (which is to allow all VLANs), the new VLAN is carried on all trunk ports. Depending on the topology of the network, this could create a loop in the new VLAN that would not be broken, particularly if there are several adjacent switches that all have run out of spanning-tree instances. You can prevent this possibility by setting allowed lists on the trunk ports of switches that have used up their allocation of spanning-tree instances.

If the number of VLANs on the switch exceeds the number of supported spanning-tree instances, we recommend that you configure the IEEE 802.1s Multiple STP (MSTP) on your switch to map multiple VLANs to a single spanning-tree instance. For more information about MSTP, see Chapter17, “Configuring MSTP”

Note MSTP is supported only on NNIs on ENIs on which STP has been enabled.

• Each routed port on the switch creates an internal VLAN for its use. These internal VLANs use extended-range VLAN numbers, and the internal VLAN ID cannot be used for an extended-range VLAN. If you try to create an extended-range VLAN with a VLAN ID that is already allocated as an internal VLAN, an error message is generated, and the command is rejected.

– Because internal VLAN IDs are in the lower part of the extended range, we recommend that you create extended-range VLANs beginning from the highest number (4094) and moving to the lowest (1006) to reduce the possibility of using an internal VLAN ID.

– Before configuring extended-range VLANs, enter the show vlan internal usage privileged EXEC command to see which VLANs have been allocated as internal VLANs.

– If necessary, you can shut down the routed port assigned to the internal VLAN, which frees up the internal VLAN, and then create the extended-range VLAN and re-enable the port, which then uses another VLAN as its internal VLAN. See the “Creating an Extended-Range VLAN with an Internal VLAN ID” section.

• Although the switch supports a total of 1005 (normal-range and extended-range) VLANs, the number of routed ports, SVIs, and other configured features affects the use of the switch hardware. If you try to create an extended-range VLAN and there are not enough hardware resources available, an error message is generated, and the extended-range VLAN is rejected.

Creating or Modifying an Ethernet VLAN

To access VLAN configuration mode, enter the vlan global configuration command with a VLAN ID. Enter a new VLAN ID to create a VLAN, or enter an existing VLAN ID to modify that VLAN. You can use the default VLAN configuration ( Table 13-2 ) or enter commands to configure the VLAN.

Note Extended-range VLANs use the default Ethernet VLAN characteristics and the MTU, the private VLAN, the RSPAN, and the UNI-ENI VLAN configurations are the only parameters you can change.

For more information about commands available in this mode, see the vlan command description in the command reference for this release. When you have finished the configuration, you must exit VLAN configuration mode for the configuration to take effect. To display the VLAN configuration, enter the show vlan privileged EXEC command.

The configurations of VLAN IDs 1 to 1005 are always saved in the VLAN database (vlan.dat file) with a VLAN number and name and in the switch running configuration file. Extended-range VLANs are not saved in the VLAN database; they are saved in the switch running configuration file. You can save the VLAN configuration in the switch startup configuration file by using the copy running-config startup-config privileged EXEC command.

Note Before you create an extended-range VLAN, you can verify that the VLAN ID is not used internally by entering the show vlan internal usage privileged EXEC command. If the VLAN ID is used internally and you want to release it, go to the “Creating an Extended-Range VLAN with an Internal VLAN ID” section before creating the extended-range VLAN.

Beginning in privileged EXEC mode, follow these steps to create or modify an Ethernet VLAN:

To delete a VLAN, use the no vlan vlan-id global configuration command. You cannot delete VLAN 1 or VLANs 1002 to 1005.

Caution When you delete a VLAN, any ports assigned to that VLAN become inactive. They remain associated with the VLAN (and thus inactive) until you assign them to a new VLAN.

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To return the VLAN name to the default settings, use the no name or no mtu VLAN configuration command.

This example shows how to create Ethernet VLAN 20, name it test20, and add it to the VLAN database:

This example shows how to create a new extended-range VLAN with all default characteristics, enter config-vlan mode, and save the new VLAN in the switch startup configuration file:

Assigning Static-Access Ports to a VLAN

You can assign a static-access port to a VLAN.

Note If you assign an interface to a VLAN that does not exist, the new VLAN is created. (See the “Creating or Modifying an Ethernet VLAN” section.)

Beginning in privileged EXEC mode, follow these steps to assign a port to a VLAN in the VLAN database:

To return an interface to its default configuration, use the default interfac e interface-id interface configuration command.

This example shows how to configure a port as an access port in VLAN 2:

Creating an Extended-Range VLAN with an Internal VLAN ID

If you enter an extended-range VLAN ID that is already assigned to an internal VLAN, an error message appears, and the extended-range VLAN is rejected. To manually release an internal VLAN ID, you must temporarily shut down the routed port that is using the internal VLAN ID.

Beginning in privileged EXEC mode, follow these steps to release a VLAN ID that is assigned to an internal VLAN and to create an extended-range VLAN with that ID:

Configuring UNI-ENI VLANs

By default, every VLAN configured on the switch is a UNI-ENI isolated VLAN. You can change VLAN configuration to that of a UNI-ENI community VLAN, a private VLAN. or an RSPAN VLAN. You can also change the configuration of one of these VLANs to the default of a UNI-ENI isolated VLAN.

Configuration Guidelines

These are the guidelines for UNI-ENI VLAN configuration:

• UNI-ENI isolated VLANs have no effect on NNI ports.
• A UNI-ENI community VLAN is like a traditional VLAN except that it can include no more than a combination of eight UNIs and ENIs.
• To change a VLAN type, first enter the vlan vlan-id global configuration command to enter VLAN configuration mode:

– To change a VLAN from UNI-ENI isolated VLAN to a private VLAN, enter the private-vlan VLAN configuration command.

– To change a UNI-ENI community VLAN to a private VLAN, you must first remove the community VLAN type by entering the no uni-vlan VLAN configuration command. Then enter the private-vlan VLAN configuration command.

– To change a VLAN from a UNI-ENI isolated VLAN to an RSPAN VLAN, enter the rspan-vlan VLAN configuration command.

– To change a UNI-ENI community VLAN to an RSPAN VLAN, you must first remove the community VLAN type by entering the no uni-vlan VLAN configuration command. Then enter the rspan-vlan VLAN configuration command.

– To change a private VLAN to a UNI-ENI VLAN, you must first remove the private VLAN type by entering the no private-vlan VLAN configuration command. Then enter the uni-vlan VLAN configuration command.

– To change an RSPAN VLAN to a UNI-ENI VLAN, you must first remove the RSPAN VLAN type by entering the no rspan-vlan VLAN configuration command. Then enter the uni-vlan VLAN configuration command

• The switch supports a total of eight UNIs and ENIs in a community VLAN. You cannot configure a VLAN as a UNI-ENI community VLAN if more than eight UNIs and ENIs belong to the VLAN.
• If you attempt to add a UNI or ENI static access port to a UNI-ENI community VLAN that has a combination of eight UNIs and ENIs, the configuration is refused. If a UNI or ENI dynamic access port is added to a UNI-ENI community VLAN that has eight UNIs or ENIs, the port is error-disabled.
• Use caution when configuring ENIs and UNIs in the same community VLAN. Local switching takes place between the ENIs and UNIs in the community VLAN and ENIs can support spanning tree while UNIs do not.

Configuring UNI-ENI VLANs

By default, every VLAN created on the switch is a UNI-ENI isolated VLAN. You can change the configuration to UNI-ENI community VLAN or to a private VLAN or RSPAN VLAN. For procedures for configuring private VLANs or RSPAN VLANs, see Chapter 14, “Configuring Private VLANs” and Chapter1, “Configuring SPAN and RSPAN”

Beginning in privileged EXEC mode, follow these steps to change the type of a UNI-ENI VLAN:

Use the no uni-vlan VLAN configuration command to return to the default (UNI-ENI isolated VLAN). Entering uni-vlan isolated command has the same effect as entering the no uni-vlan VLAN configuration command. The show vlan and show vlan vlan-id privileged EXEC commands also display UNI-ENI VLAN information, but only UNI-ENI community VLANs appear. To display both isolated and community VLANs, use the show vlan uni-vlan type command.

Trunking Overview

A trunk is a point-to-point link between one or more Ethernet switch interfaces and another networking device such as a router or a switch. Ethernet trunks carry the traffic of multiple VLANs over a single link, and you can extend the VLANs across an entire network. The switch supports the IEEE 802.1Q industry-standard trunking encapsulation.

You can configure a trunk on a single Ethernet interface or on an EtherChannel bundle. For more information about EtherChannels, see Chapter1, “Configuring EtherChannels and Link-State Tracking”

Ethernet interfaces support different trunking modes (see Table 13-4 ). You can set an interface as trunking or nontrunking.

• If you do not intend to trunk across links, use the switchport mode a ccess interface configuration command to disable trunking.
• To enable trunking, use the switchport mode trunk interface configuration command to change the interface to a trunk.

IEEE 802.1Q Configuration Considerations

The IEEE 802.1Q trunks impose these limitations on the trunking strategy for a network:

• In a network of Cisco switches connected through IEEE 802.1Q trunks, the switches maintain one spanning-tree instance for each VLAN allowed on the trunks. Non-Cisco devices might support one spanning-tree instance for all VLANs.

When you connect a Cisco switch to a non-Cisco device through an IEEE 802.1Q trunk, the Cisco switch combines the spanning-tree instance of the VLAN of the trunk with the spanning-tree instance of the non-Cisco IEEE 802.1Q switch. However, spanning-tree information for each VLAN is maintained by Cisco switches separated by a cloud of non-Cisco IEEE 802.1Q switches. The non-Cisco IEEE 802.1Q cloud separating the Cisco switches is treated as a single trunk link between the switches.

• Make sure that the native VLAN for an IEEE 802.1Q trunk is the same on both ends of the trunk link. If the native VLAN on one end of the trunk is different from the native VLAN on the other end, spanning-tree loops might result.
• Disabling spanning tree on the native VLAN of an IEEE 802.1Q trunk without disabling spanning tree on every VLAN in the network can potentially cause spanning-tree loops. We recommend that you leave spanning tree enabled on the native VLAN of an IEEE 802.1Q trunk or disable spanning tree on every VLAN in the network. Make sure that your network is loop-free before disabling spanning tree.

Default Layer 2 Ethernet Interface VLAN Configuration

Table 13-5 shows the default Layer 2 Ethernet interface VLAN configuration.

Configuring an Ethernet Interface as a Trunk Port

• Interaction with Other Features
• Defining the Allowed VLANs on a Trunk
• Configuring the Native VLAN for Untagged Traffic
• Configuring the Native VLAN for Untagged Traffic

Interaction with Other Features

Trunking interacts with other features in these ways:

• A trunk port cannot be a secure port.
• A trunk port cannot be a tunnel port.
• Trunk ports can be grouped into EtherChannel port groups, but all trunks in the group must have the same configuration. When a group is first created, all ports follow the parameters set for the first port to be added to the group. If you change the configuration of one of these parameters, the switch propagates the setting that you entered to all ports in the group:

– allowed-VLAN list.

– STP port priority for each VLAN.

– STP Port Fast setting.

Note STP is supported by default on NNIs, but must be enabled on ENIs. STP is not supported on UNIs.

– trunk status: if one port in a port group ceases to be a trunk, all ports cease to be trunks.

• If you try to enable IEEE 802.1x on a trunk port, an error message appears, and IEEE 802.1x is not enabled. If you try to change the mode of an IEEE 802.1x-enabled port to trunk, the port mode is not changed.

Configuring a Trunk Port

Beginning in privileged EXEC mode, follow these steps to configure a port as an IEEE 802.1Q trunk port:

To return an interface to its default configuration, use the default interface interface-id interface configuration command. To reset all trunking characteristics of a trunking interface to the defaults, use the no switchport trunk interface configuration command. To disable trunking, use the switchport mode access interface configuration command to configure the port as a static-access port.

This example shows how to configure a port as an IEEE 802.1Q trunk with VLAN 33 as the native VLAN:

Defining the Allowed VLANs on a Trunk

By default, a trunk port sends traffic to and receives traffic from all VLANs. All VLAN IDs, 1 to 4094, are allowed on each trunk. However, you can remove VLANs from the allowed list, preventing traffic from those VLANs from passing over the trunk. To restrict the traffic a trunk carries, use the switchport trunk allowed vlan remove vlan-list interface configuration command to remove specific VLANs from the allowed list.

Note VLAN 1 is the default VLAN on all trunk ports in all Cisco switches, and it has previously been a requirement that VLAN 1 always be enabled on every trunk link. The VLAN 1 minimization feature allows you to disable VLAN 1 on any individual VLAN trunk link so that no user traffic (including spanning-tree advertisements) is sent or received on VLAN 1. You do this by removing VLAN 1 from the allowed VLAN list.

To reduce the risk of spanning-tree loops or storms, you can disable VLAN 1 on any individual VLAN trunk port by removing VLAN 1 from the allowed list. When you remove VLAN 1 from a trunk port, the interface continues to send and receive management traffic, for example, Cisco Discovery Protocol (CDP), Port Aggregation Protocol (PAgP), and Link Aggregation Control Protocol (LACP) in VLAN 1.

If a trunk port with VLAN 1 disabled is converted to a nontrunk port, it is added to the access VLAN. If the access VLAN is set to 1, the port is added to VLAN 1, regardless of the switchport trunk allowed setting. The same is true for any VLAN that has been disabled on the port.

A trunk port can become a member of a VLAN if the VLAN is enabled and if the VLAN is in the allowed list for the port.

Beginning in privileged EXEC mode, follow these steps to modify the allowed list of an IEEE 802.1Q trunk:

To return to the default allowed VLAN list of all VLANs, use the no switchport trunk allowed vlan interface configuration command.

This example shows how to remove VLAN 2 from the allowed VLAN list on a port:

Configuring the Native VLAN for Untagged Traffic

A trunk port configured with IEEE 802.1Q tagging can receive both tagged and untagged traffic. By default, the switch forwards untagged traffic in the native VLAN configured for the port. The native VLAN is VLAN 1 by default.

Note The native VLAN can be assigned any VLAN ID.

For information about IEEE 802.1Q configuration issues, see the “IEEE 802.1Q Configuration Considerations” section.

Beginning in privileged EXEC mode, follow these steps to configure the native VLAN on an IEEE 802.1Q trunk:

To return to the default native VLAN, VLAN 1, use the no switchport trunk native vlan interface configuration command.

If a packet has a VLAN ID that is the same as the sending port native VLAN ID, the packet is sent untagged; otherwise, the switch sends the packet with a tag.

Configuring Trunk Ports for Load Sharing

Load sharing divides the bandwidth supplied by parallel trunks that connect switches. To avoid loops, STP normally blocks all but one parallel link between switches. Using load sharing, you divide the traffic between the links according to the VLAN to which the traffic belongs.

You configure load sharing on trunk ports that have STP enabled by using STP port priorities or STP path costs. For load sharing using STP port priorities, both load-sharing links must be connected to the same switch. For load sharing using STP path costs, each load-sharing link can be connected to the same switch or to two different switches. For more information about STP, see Chapter16, “Configuring STP”

Load Sharing Using STP Port Priorities

When two ports on the same switch form a loop, the switch uses the STP port priority to decide which port is enabled and which port is in a blocking state. You can set the priorities on a parallel STP trunk port so that the port carries all the traffic for a given VLAN. The trunk port with the higher priority (lower values) for a VLAN is forwarding traffic for that VLAN. The trunk port with the lower priority (higher values) for the same VLAN remains in a blocking state for that VLAN. One trunk port sends or receives all traffic for the VLAN.

Figure 13-3 shows two trunks connecting supported switches. In this example, the switches are configured as follows:

• VLANs 8 through 10 are assigned a port priority of 16 on Trunk 1.
• VLANs 3 through 6 retain the default port priority of 128 on Trunk 1.
• VLANs 3 through 6 are assigned a port priority of 16 on Trunk 2.
• VLANs 8 through 10 retain the default port priority of 128 on Trunk 2.

In this way, Trunk 1 carries traffic for VLANs 8 through 10, and Trunk 2 carries traffic for VLANs 3 through 6. If the active trunk fails, the trunk with the lower priority takes over and carries the traffic for all of the VLANs. No duplication of traffic occurs over any trunk port.

Figure 13-3 Load Sharing by Using STP Port Priorities

Beginning in privileged EXEC mode on Switch A, follow these steps to configure the network shown in Figure 13-3. Note that you can use any interface numbers; those shown are examples only.

Follow the same steps on Switch B to configure the trunk port for Trunk 1 with a spanning-tree port priority of 16 for VLANs 8 through 10, and the configure trunk port for Trunk 2 with a spanning-tree port priority of 16 for VLANs 3 through 6.

Load Sharing Using STP Path Cost

You can configure parallel trunks to share VLAN traffic by setting different path costs on a trunk and associating the path costs with different sets of VLANs, blocking different ports for different VLANs. The VLANs keep the traffic separate and maintain redundancy in the event of a lost link.

In Figure 13-4, Trunk ports 1 and 2 are configured as 100Base-T ports. These VLAN path costs are assigned:

• VLANs 2 through 4 are assigned a path cost of 30 on Trunk port 1.
• VLANs 8 through 10 retain the default 100Base-T path cost on Trunk port 1 of 19.
• VLANs 8 through 10 are assigned a path cost of 30 on Trunk port 2.
• VLANs 2 through 4 retain the default 100Base-T path cost on Trunk port 2 of 19.

Figure 13-4 Load-Sharing Trunks with Traffic Distributed by Path Cost

Beginning in privileged EXEC mode, follow these steps to configure the network shown in Figure 13-4:

Follow the same steps on Switch B to configure the trunk port for Trunk 1 with a path cost of 30 for VLANs 2 through 4, and configure the trunk port for Trunk 2 with a path cost of 30 for VLANs 8 through 10.

Understanding VMPS

Each time the client switch receives the MAC address of a new host, it sends a VQP query to the VMPS. When the VMPS receives this query, it searches its database for a MAC-address-to-VLAN mapping. The server response is based on this mapping and whether or not the server is in open or secure mode. In secure mode, the server shuts down the port when an illegal host is detected. In open mode, the server simply denies the host access to the port.

If the port is currently unassigned (that is, it does not yet have a VLAN assignment), the VMPS provides one of these responses:

• If the host is allowed on the port, the VMPS sends the client a vlan-assignment response containing the assigned VLAN name and allowing access to the host.
• If the host is not allowed on the port and the VMPS is in open mode, the VMPS sends an access-denied response.
• If the VLAN is not allowed on the port and the VMPS is in secure mode, the VMPS sends a port-shutdown response.

If the port already has a VLAN assignment, the VMPS provides one of these responses:

• If the VLAN in the database matches the current VLAN on the port, the VMPS sends an success response, allowing access to the host.
• If the VLAN in the database does not match the current VLAN on the port and active hosts exist on the port, the VMPS sends an access-denied or a port-shutdown response, depending on the secure mode of the VMPS.

If the switch receives an access-denied response from the VMPS, it continues to block traffic to and from the host MAC address. The switch continues to monitor the packets directed to the port and sends a query to the VMPS when it identifies a new host address. If the switch receives a port-shutdown response from the VMPS, it disables the port. The port must be manually re-enabled by using the CLI or SNMP.

Dynamic-Access Port VLAN Membership

A dynamic-access port can belong to only one VLAN with an ID from 1 to 4094. When the link comes up, the switch does not forward traffic to or from this port until the VMPS provides the VLAN assignment. The VMPS receives the source MAC address from the first packet of a new host connected to the dynamic-access port and attempts to match the MAC address to a VLAN in the VMPS database.

Note Only UNIs or ENIs can be dynamic-access ports.

If there is a match, the VMPS sends the VLAN number for that port. If the client switch was not previously configured, it uses the domain name from the first VTP packet it receives on its trunk port from the VMPS. If the client switch was previously configured, it includes its domain name in the query packet to the VMPS to obtain its VLAN number. The VMPS verifies that the domain name in the packet matches its own domain name before accepting the request and responds to the client with the assigned VLAN number for the client. If there is no match, the VMPS either denies the request or shuts down the port (depending on the VMPS secure mode setting).

Multiple hosts (MAC addresses) can be active on a dynamic-access port if they are all in the same VLAN; however, the VMPS shuts down a dynamic-access port if more than 20 hosts are active on the port.

If the link goes down on a dynamic-access port, the port returns to an isolated state and does not belong to a VLAN. Any hosts that come online through the port are checked again through the VQP with the VMPS before the port is assigned to a VLAN.

Dynamic-access ports can be used for direct host connections, or they can connect to a network. A maximum of 20 MAC addresses are allowed per port on the switch. A dynamic-access port can belong to only one VLAN at a time, but the VLAN can change over time, depending on the MAC addresses seen.

Default VMPS Client Configuration

Table 13-6 shows the default VMPS and dynamic-access port configuration on client switches.

VMPS Configuration Guidelines

These guidelines and restrictions apply to dynamic-access port VLAN membership:

• You should configure the VMPS before you configure ports as dynamic-access ports.
• IEEE 802.1x ports cannot be configured as dynamic-access ports. If you try to enable IEEE 802.1x on a dynamic-access (VQP) port, an error message appears, and IEEE 802.1x is not enabled. If you try to change an IEEE 802.1x-enabled port to dynamic VLAN assignment, an error message appears, and the VLAN configuration is not changed.
• Trunk ports cannot be dynamic-access ports, but you can enter the switchport access vlan dynamic interface configuration command for a trunk port. In this case, the switch retains the setting and applies it if the port is later configured as an access port.

You must turn off trunking on the port before the dynamic-access setting takes effect.

• Dynamic-access ports cannot be monitor ports.
• Secure ports cannot be dynamic-access ports. You must disable port security on a port before it becomes dynamic.
• Private VLAN ports cannot be dynamic-access ports.
• Dynamic-access ports cannot be members of an EtherChannel group.
• Port channels cannot be configured as dynamic-access ports.

Configuring the VMPS Client

You configure dynamic VLANs by using the VMPS (server). The switch can be a VMPS client; it cannot be a VMPS server.

Entering the IP Address of the VMPS

You must first enter the IP address of the server to configure the switch as a client.

Beginning in privileged EXEC mode, follow these steps to enter the IP address of the VMPS:

Note You must have IP connectivity to the VMPS for dynamic-access ports to work. You can test for IP connectivity by pinging the IP address of the VMPS and verifying that you get a response.

Configuring Dynamic-Access Ports on VMPS Clients

Caution D ynamic-access port VLAN membership is for end stations or hubs connected to end stations. Connecting dynamic-access ports to other switches can cause a loss of connectivity.

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Beginning in privileged EXEC mode, follow these steps to configure a dynamic-access port on a VMPS client switch:

To return an interface to its default configuration, use the default interface interface-id interface configuration command. To reset the access mode to the default VLAN for the switch, use the no switchport access vlan interface configuration command.

Reconfirming VLAN Memberships

Beginning in privileged EXEC mode, follow these steps to confirm the dynamic-access port VLAN membership assignments that the switch has received from the VMPS:

Changing the Reconfirmation Interval

VMPS clients periodically reconfirm the VLAN membership information received from the VMPS.You can set the number of minutes after which reconfirmation occurs.

Beginning in privileged EXEC mode, follow these steps to change the reconfirmation interval:

To return the switch to its default setting, use the no vmps reconfirm global configuration command.

Changing the Retry Count

Beginning in privileged EXEC mode, follow these steps to change the number of times that the switch attempts to contact the VMPS before querying the next server:

To return the switch to its default setting, use the no vmps retry global configuration command.

Monitoring the VMPS

You can display information about the VMPS by using the show vmps privileged EXEC command. The switch displays this information about the VMPS:

• VMPS VQP Version—the version of VQP used to communicate with the VMPS. The switch queries the VMPS that is using VQP Version 1.
• Reconfirm Interval—the number of minutes the switch waits before reconfirming the VLAN-to-MAC-address assignments.
• Server Retry Count—the number of times VQP resends a query to the VMPS. If no response is received after this many tries, the switch starts to query the secondary VMPS.
• VMPS domain server—the IP address of the configured VLAN membership policy servers. The switch sends queries to the one marked current. The one marked primary is the primary server.
• VMPS Action—the result of the most recent reconfirmation attempt. A reconfirmation attempt can occur automatically when the reconfirmation interval expired, or you can force it by entering the vmps reconfirm privileged EXEC command.

This is an example of output for the show vmps privileged EXEC command:

Troubleshooting Dynamic-Access Port VLAN Membership

The VMPS shuts down a dynamic-access port under these conditions:

• The VMPS is in secure mode, and it does not allow the host to connect to the port. The VMPS shuts down the port to prevent the host from connecting to the network.
• More than 20 active hosts reside on a dynamic-access port.

To disable and re-enable a disabled dynamic-access port, enter the shutdown interface configuration command followed by the no shutdown interface configuration command.

VMPS Configuration Example

Figure 13-5 shows a network with a VMPS server switch and VMPS client switches with dynamic-access ports. In this example, these assumptions apply:

• The VMPS server and the VMPS client are separate switches.
• The Catalyst 6500 series Switch A is the primary VMPS server.
• The Catalyst 6500 series Switch C and Switch J are secondary VMPS servers.
• End stations are connected to the clients, Switch B and Switch I.
• The database configuration file is stored on the TFTP server with the IP address 172.20.22.7.

Figure 13-5 Dynamic Port VLAN Membership Configuration