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This chapter describes virtual LAN (VLAN) features and functionality, the Virtual LAN Menu of the Catalyst 1900 and Catalyst 2820 switches, and procedures for creating VLANs and assigning ports to VLANs.
You can assign each switch port to a VLAN. Ports in a VLAN share broadcast traffic. Ports that do not belong to that VLAN do not share the broadcast traffic. Ports from multiple Catalyst 1900 and Catalyst 2820 switches can be members of the same VLAN. Figure 2-1 shows an example of VLANs that span multiple switches and multiple floors or a building.
VLANs provide the following features:
Table 2-1 shows the capabilities and defaults for the Catalyst 1900 and Catalyst 2820 series VLAN features.
| Feature | Capability | Default |
|---|---|---|
Trunk ports | Supports a maximum of two trunks. The Catalyst 1900 switch supports a maximum of two Inter-Switch Link (ISL) trunks. The Catalyst 2820 switch supports both ISL and Asynchronous Transfer Mode (ATM) LAN emulation (LANE) trunk connections and ATM permanent virtual connections (PVCs). Fast Ethernet trunk ports can be grouped using the Fast EtherChannel feature to form a single trunk. | No trunk ports are enabled. |
Supports Spanning-Tree Protocol (STP) on VLAN trunks to load share. | No load sharing is set up. | |
Supports server, client, and transparent modes. Server and transparent modes support a maximum of 128 VLANs. From server mode, the switch automatically transitions to client mode if it learns more than 128 VLANs from advertisements. Client mode supports 1005 VLANs. | Configured to server mode. Set to no-management domain state. | |
Supports pruning. | Pruning is disabled. | |
Supports dynamic and static ports. | The default VLAN membership of all ports is static, and all ports reside in VLAN 1. | |
VLAN Membership Policy Server (VMPS) | Does not function as a VMPS on the network. (The Catalyst 5000 series switches support this feature.) | No default. |
Runs on a maximum of 64 VLANs at one time. | VLANs 1 to 64 are enabled with STP. |
Networks that have VLANs contain one or more of the following components:
Use the Virtual LAN Menu to perform the following tasks, which are described in this chapter:
To access the Virtual LAN Menu, enter [V] Virtual LAN at the selection prompt on the Main Menu. The following display appears:
Catalyst 1900 - Virtual LAN Configuration --------------------Information---------------- VTP version: 1 Configuration revision: 1 Maximum VLANs supported locally: 1005 Number of existing VLANs: 6 Configuration last modified by: 0.0.0.0 at 01-03-2000 18:35:56 --------------------Settings------------------ [N] Domain name [V] VTP mode control Server [F] VTP pruning mode Disabled [O] VTP traps Enabled --------------------Actions------------------- [L] List VLANs [A] Add VLAN [M] Modify VLAN [D] Delete VLAN [E] VLAN Membership [S] VLAN Membership Servers [T] Trunk Configuration [W] VTP password [P] VTP Statistics [X] Exit to Main Menu Enter Selection:
When configuring the functions displayed on the menu, you might not use the options in the order in which they appear in the menu. Many of the menu entries prompt you for an additional selection and then return you to the Virtual LAN Menu for the next step.
When creating a VLAN, you must first determine and configure the management domain on the switch. Management domains group VLANs into zones of different administrative responsibilities. Catalyst 1900 and Catalyst 2820 switches support only one management domain for each switch.
Catalyst 1900 and Catalyst 2820 switches operate in one of three modes: server, client, or transparent mode. By default, a switch in the no-management domain state is a VTP server; that is, it learns from received advertisements on a configured trunk port. If trunks are configured on the switch, VTP receives and transmits VLAN advertisements. From the server mode, you can add or delete VLANs by using the VTP Management Information Base (MIB) SNMP management station, the command-line interface (CLI), or the console menus.
A switch configured in VTP server mode advertises VLAN configuration to neighboring switches through its trunks and learns new VLAN configurations from those neighbors. Use the server mode to add or delete VLANs and to modify VLAN information by using the VTP MIB, the CLI, or the console menus. For example, when you add a VLAN, VTP advertises the new VLAN to other switches, and both servers and clients prepare to receive traffic on their trunk ports.
In VTP transparent mode, the switch does not advertise or learn VLAN configurations from the network. When a switch is in VTP transparent mode, you can modify, add, or delete VLANs through the console menus, the CLI, or the MIB.
When a switch is in the no-management domain state and running in either server or client mode, it inherits a management domain name and configuration revision number upon receiving an advertisement from a configured trunk port. The configuration revision number reflects the latest revision of the VTP configuration. If a management domain for the switch is defined, the switch ignores advertisements with a different management domain or a lower configuration revision number and checks all received advertisements with the same management domain for consistency. If the information contained in the received advertisement is consistent, the switch propagates the advertisements to other trunk ports and adds the newly learned information locally. Because all devices in the same management domain learn about any new VLANs configured in the transmitting device, you need to configure a new VLAN on only one device in the management domain.
| Step | Action | ||
|---|---|---|---|
| Select [V] Virtual LAN Menu from the Main Menu. | ||
| a. Select [N] Domain Name Menu from the Virtual LAN Menu. b. Enter the management domain name at the selection prompt. c. Press Return. The Virtual LAN Menu reappears. |
To verify that you have assigned the management domain, view the domain name on the Virtual LAN Configuration Menu.
To create a new VLAN, you need to define the VLAN characteristics. The Enterprise Edition software prompts you to define these characteristics:
To define a VLAN, you need to specify its attributes. Complete the following steps to set the VLAN number, name, IEEE 802.10 SAID value, and MTU size.
| Step | Action | ||
|---|---|---|---|
| Select [V] Virtual LAN Menu from the Main Menu. | ||
| Select [A] Add VLAN from the Virtual LAN Menu. | ||
| Enter the type of VLAN at the selection prompt. For Ethernet, enter [1] Ethernet. Press Return. | ||
| At the next menu, select [N] VLAN Number, and enter the number of the VLAN to be added. Press Return. | ||
| At the next menu, select [V] VLAN Name, and enter the name of the VLAN to be added. Press Return. | ||
| At the next menu, select [I] 802.10 SAID, and enter the appropriate value. The value must be within the range shown on the screen, and the value cannot be the same as the value of another IEEE 802.10 value. After you enter the value, press Return. | ||
| At the next menu, select [M] MTU Size, and enter the appropriate value. Press Return. | ||
| At the next menu, select [T] VLAN State, and select Enabled. Press Return. | ||
| Select [S] Save. |
To verify that you have configured the VLAN, view the VLAN settings on the Virtual LAN Configuration Menu. To do this, select [L] List VLANs from the Virtual LAN Menu to access the list of defined VLANs. Verify that the defined VLAN was added to the list. To get a complete list of parameters for a particular VLAN, select [M] Modify VLANs.
Before configuring a VLAN, you need to determine its structure and consider how to group users into VLANs. Based on access, security, and bandwidth requirements, decide which users need to be part of the same VLAN according to these considerations:
Figure 2-2 shows a local VLAN configuration that groups switch ports into VLAN 10 and VLAN 20.
A VLAN created in a management domain remains unused until it is mapped to switch ports. The VLAN Membership menu maps the VLANs to ports. The default configuration has all switched Ethernet ports statically assigned to VLAN 1. If a port is assigned to a VLAN that is not created or to a VLAN in a suspended state, that port acquires the disabled-no-VLAN status. The port cannot forward or receive traffic until the VLAN assigned to that port is enabled.
To group the switch ports to VLANs, do the following:
| Step | Action | ||
|---|---|---|---|
| Select [V] Virtual LAN from the Main Menu. | ||
| Select [E] VLAN Membership. | ||
| Select [V] VLAN Assignment. | ||
| Enter the appropriate port numbers at the selection prompt, and select the VLAN to group the ports at the next selection prompt. Press Return. |
A Fast Ethernet port can function as an ISL trunk, a static VLAN member port, or a dynamic VLAN member port. An ATM module can function as a LANE trunk or a static VLAN member port. You can configure a Fast Ethernet port as a static VLAN member port by following the steps listed. To configure an ATM port as a static VLAN member port, you must also configure a LANE client. For more information on configuring LANE clients, refer to the Catalyst 2820 ATM Modules Installation and Configuration Guide.
To verify that you have grouped switch ports to VLANs, do the following:
| Step | Action | ||
|---|---|---|---|
| Select [V] Virtual LAN from the Main Menu. | ||
| Select [E] VLAN Membership. |
A VLAN trunk can connect two Catalyst 1900 or Catalyst 2820 switches; it can also connect these switches to a Catalyst 5000 series switch or to a router. For concepts about VLAN with load sharing, refer to "VLAN Trunking and Load Sharing" later in this section.
The Catalyst 1900 and Catalyst 2820 switches support two Fast Ethernet ISL trunks. A trunk can be a one-port Fast Ethernet TX, a one-port Fast Ethernet FX, or an ATM module. Refer to the Catalyst 2820 ATM Modules Installation and Configuration Guide to determine the firmware version that supports trunking.
For each enabled VLAN that is known to the VTP and included in the allowed list for the trunk port, a Fast Ethernet ISL trunk automatically carries traffic for the VLAN and extends VLANs from one Catalyst switch to another.
For an ATM trunk to carry traffic for a VLAN, all of the following conditions must be met:
The ATM trunk module does not forward frames from the switch for a VLAN until you define a LANE client. Each VLAN must be associated with either a LANE client or a PVC before the ATM trunk module forwards traffic to and from a VLAN. When creating a LANE client or PVC on the module, a VLAN number is needed to map the ATM connection to a VLAN. For more information on configuring LANE clients, refer to the Catalyst 2820 ATM Modules Installation and Configuration Guide.
To configure support for RFC 1483, you must bind PVCs to the VLAN, and the VLAN ID must match the VLAN ID used on the switch. Each ATM trunk module supports a maximum of 64 active VLANs at one time.
Figure 2-3 shows the Catalyst 2820 switch using ATM trunking.
There are three ways to configure load sharing using trunk ports. One way uses STP port priorities; the second way uses STP path costs. (For a third method, refer to the "Fast EtherChannel Feature" section in "Additional Features.") If you configure load sharing using STP port priorities, both load-sharing links must be connected to the same switch. If you configure load sharing using STP path costs, each load-sharing link can be connected to the same switch or to two different switches.
To use load sharing with port priorities, you must use STP parameters on a VLAN basis. These parameters define which VLANs have priority access to a trunk and which VLANs use the trunk as a backup.
Figure 2-4 shows two trunks that are connected to the switched 100BaseTX ports on two Catalyst 1900 switches. The port cost of carrying VLAN traffic across these trunks is equal.
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 lower priority takes over and carries the traffic for all of the VLANs.
Catalyst 1900 and Catalyst 2820 switches use load sharing on parallel trunks. By setting STP parameters on a VLAN basis, you can define which VLANs have priority access to a trunk and which VLANs use the trunk as a backup when another trunk fails.
To assign a priority to a port, do the following:
| Step | Action | ||
|---|---|---|---|
| Enter [P] Port Configuration at the selection prompt in the Main Menu. | ||
| Enter the port number at the selection prompt, and press Return. | ||
| Enter [T] Trunk STP Configuration at the selection prompt. | ||
| a. Select [I] Port Priority (spanning tree) - option 1. b. Enter the port priority at the selection prompt. Press Return. c. Select [J] Port Priority (spanning tree) - option 2. d. Enter the port priority at the selection prompt. Press Return. | ||
| a. Select [M] Assign VLANs to option 1 port priority. b. Enter the VLAN numbers that are to use port priority option 1 at the selection prompt. Press Return. c. Select [O] Assign VLANs to option 2 port priority. d. Enter the VLAN numbers that are to use port priority option 2 at the selection prompt. Press Return. |
To verify the port priority option values and the assignment of VLANs to port priority options 1 and 2, access the Trunk Port STP Configuration Menu, and select [E] Show VLAN port priorities to show the assignment of VLANs to port priority options.
You can configure load sharing between trunk ports by assigning two STP path costs (path-cost option 1 and path-cost option 2) to each trunk and then assigning different VLANs to the different path costs.
By default, trunk ports are assigned the same STP path costs for option 1 and option 2. Consequently, STP selects the path for VLAN traffic by using the Bridge ID. All VLANs then use the same path to forward traffic, as shown in Figure 2-5.
You can configure VLAN 1 to use a different path than VLAN 2 by assigning two path costs per trunk and assigning each VLAN to use a different path cost on each trunk, as shown in Figure 2-6.
To configure load sharing using path costs, do the following:
The trunk state on the remote end of the trunk connection (that is, on the other switch) must be in a state that allows trunking. Refer to the "DISL Port States" section for more information on this subject.
The following example configures load sharing by configuring the following parameters:
| Step | Action | ||
|---|---|---|---|
| Select [V] Virtual LAN from the Main Menu. | ||
| Enter [T] Trunk Configuration. | ||
| At the next menu, enter [A], and press Return. | ||
| Enter [T] Trunking. | ||
| At the next menu, select a state:
Press Return. | ||
| At the next menu, enter [N] Next Trunk. | ||
| Enter [T] Trunking. | ||
| At the next menu, select a state:
Press Return. | ||
| Enter [X] Exit, twice. | ||
| Enter [P] Port Configuration. | ||
| At the next menu, enter [A], and press Return. | ||
| Enter [T] Trunk STP configuration. | ||
| At the next menu, select [B] Path cost (spanning tree) - option 2. | ||
| At the prompt, enter 100, and press Return. | ||
| a. Select [T] Assign VLANs to option 1 Path cost. b. Enter 1 and press Return. | ||
| a. Select [Y] Assign VLANs to option 2 Path cost. b. Enter 2 and press Return. | ||
| a. Enter [N] Next Trunk. | ||
| At the next menu, select [B] Path cost (spanning tree) - option 2. | ||
| At the prompt, enter 100, and press Return. | ||
| a. Select [Y] Assign VLANs to option 2 Path cost. b. Enter 1, and press Return. | ||
| a. Select [T] Assign VLANs to option 1 Path cost. b. Enter 2, and press Return. |
Table 2-2 summarizes the VLAN and path-costs assigned in this example.
| Path Cost = 10 | Path Cost = 100 | |
|---|---|---|
| Trunk A | VLAN 1 | VLAN 2 |
| Trunk B | VLAN 2 | VLAN 1 |
Load sharing is achieved as follows:
The Cisco Catalyst 1900 and 2820 Enterprise Edition Software supports a maximum of 27 switched ports. On the Catalyst 2820 switch, the only ports you can configure as trunks are the single-port 100BaseTX, 100BaseFX, and ATM modules. On the Catalyst 1900 switch, you can configure the 100BaseTX or 100Base FX ports as trunks. (Refer to the Catalyst 2820 ATM Modules Installation and Configuration Guide to determine the firmware version that supports trunking.)
The Dynamic Inter-Switch Link Protocol (DISL) protocol synchronizes the configuration of two interconnected Fast Ethernet interfaces into an ISL trunk. The DISL protocol ensures that both of the Fast Ethernet interfaces are either in trunking or nontrunking mode.
If you are using VTP to propagate VLAN information, you must enable a trunk to receive and propagate VLAN information through network advertisements. The switch then learns the management domain and the VLANs within it that are defined on all other switches. Refer to "Configuring VTP" for instruction for setting this option. ISL-capable switch ports process DISL packets from switches that have the same VTP domain name or a null domain name. If a switch port receives a DISL packet with a different VTP domain name than the domain name configured on the switch, the packet is discarded.
Figure 2-7 shows an example of a Fast Ethernet ISL configuration.
The DISL protocol requires that there is a point-to-point ISL connection between two devices. DISL-capable ports can be configured to be in any of the states described in Table 2-3.
| Port State | Description |
|---|---|
On | Configures the port in permanent ISL trunk mode and negotiates with the connected device to convert the link to trunk mode. The port converts to a trunk, even if the other end of the link does not. This state is used when an ISL port is connected to another ISL port that does not support the DISL protocol. |
Off | Disables port trunking and negotiates with the connected device to convert the link to nontrunk. The port converts to a nontrunk mode, even if the other end of the link does not. This state is used when an ISL port is connected to another ISL port that does not support the DISL protocol. (Default) |
Desirable | Triggers the port to negotiate the link from nontrunking to trunking mode. The port negotiates to a trunk port if the connected device is either in the On, Desirable, or Auto state. Otherwise, the port becomes a nontrunk port. |
Auto | Enables a port to become a trunk only if the connected device has the state set to On or Desirable. |
No-negotiate | Configures the port in permanent ISL trunk mode, but the port does not generate or process DISL frames. Use this state when an ISL port is connected to another ISL port (such as a router ISL port) that does not support the DISL protocol. |
The status of a VLAN port is shown in the grayed out field in the Status column of the web console Port Management Page. These non-configurable VLAN states indicate the DISL status of a port and whether or not the port has been disabled or suspended because no VLAN has been configured for the port. (See Table 2-4.)
| VLAN Port Status | Description |
|---|---|
Suspended-DISL | The port is suspended due to DISL negotiation. |
Suspended No-VLAN | The port is suspended because there is no VLAN assigned to the port. |
Disabled No-VLAN | The port is disabled because the VLAN assigned to the port does not exist. |
The on (or off) trunking state might cause configuration problems. Use the on or off state when an ISL port is connected to a device that you know does not support the DISL protocol. Because configurations can change, we advise you to set the trunking state to auto or desirable. If the other port does not support DISL, the port then functions as normal in static mode.
Using the on trunking state when the DISL protocol is in use might lead to ISL-mode mismatches where one end of the link is trunking while the other end is not. The situation can arise if the switch on the other end of the trunk is in no-negotiate state. Therefore, if a trunk is desired, use the desirable trunking state.
Using the off trunking state is not recommended when using DISL protocol. The risk of creating an ISL-mode mismatch is lower with the off mode, but if a trunk is not desired, use auto mode.
Table 2-5 shows the possible combinations of DISL port states for two switches, Switch 1 and Switch 2. For each port state combination, it also lists the trunking mode of the switch. An asterisk (*) indicates a misconfigured state that, if configured, results in a loss of connectivity.
| Switch 1 Port State | Switch 2 Port State | Switch 1 Mode | Switch 2 Mode |
|---|---|---|---|
Off | Off | Nontrunking | Nontrunking |
Off | On | Nontrunking | Trunking* |
Off | Desirable | Nontrunking | Nontrunking |
Off | Auto | Nontrunking | Nontrunking |
Off | No-negotiate | Nontrunking | Trunking* |
On | Off | Trunking | Nontrunking* |
On | On | Trunking | Trunking |
On | Desirable | Trunking | Trunking |
On | Auto | Trunking | Trunking |
On | No-negotiate | Trunking | Trunking |
Desirable | Off | Nontrunking | Nontrunking |
Desirable | On | Trunking | Trunking |
Desirable | Desirable | Trunking | Trunking |
Desirable | Auto | Trunking | Trunking |
Desirable | No-negotiate | Nontrunking | Trunking* |
Auto | Off | Nontrunking | Nontrunking |
Auto | On | Trunking | Trunking |
Auto | Desirable | Trunking | Trunking |
Auto | Auto | Nontrunking | Nontrunking |
Auto | No-negotiate | Nontrunking | Trunking* |
No-negotiate | Off | Trunking* | Nontrunking* |
No-negotiate | On | Trunking | Trunking |
No-negotiate | Desirable | Trunking* | Nontrunking* |
No-negotiate | Auto | Trunking | Nontrunking* |
No-negotiate | No-negotiate | Trunking | Trunking |
You cannot change the trunking state of an ATM module. The trunking state of trunk-capable ATM modules defaults to on. The trunking state of ATM modules not capable of trunking defaults to off.
To configure a trunk, do the following:
| Step | Action | ||
|---|---|---|---|
| Select [V] Virtual LAN from the Main Menu. | ||
| Enter [T] Trunk Configuration. | ||
| At the next menu, enter [A] or [B] at the selection prompt, and press Return. | ||
| Enter [T] Trunking. | ||
| At the next menu, select a setting:
Press Return. |
To verify that you have configured the selected port as a trunk port, check the trunking status and encapsulation type at the top of the Trunk Configuration screen. (When a link is present, a Fast Ethernet trunk shows ISL encapsulation. An ATM module shows LANE encapsulation.) From the Main Menu, access the Virtual LAN Menu to see the status of each active VLAN.
Each trunk has a list of VLANs called allowed VLANs that are enabled to receive and transmit all types of traffic on that trunk. You must configure the VLAN and add it to the allowed list for the trunk so that it can receive trunk traffic. By default, all configured VLANs are allowed on a trunk. To add a VLAN to the allowed list, do the following:
| Step | Action | ||
|---|---|---|---|
| Select [V] Virtual LAN from the Main Menu. | ||
| Enter [T] Trunk Configuration. | ||
| At the next menu, enter [A] or [B] at the selection prompt, and press Return. | ||
| a. Enter [A] Add Allowed VLANs at the selection prompt. b. Enter the appropriate VLAN number at the selection prompt in the next menu. The Trunk Configuration Menu reappears. |
Traffic will not be forwarded to or from a VLAN that is not included in the VLAN allowed list.
To verify that you have added a VLAN to the allowed list, select [V] List Allowed VLANs from the Trunk Configuration Menu, and examine the contents of the display.
To delete a VLAN from the allowed list, do the following:
| Step | Action | ||
|---|---|---|---|
| Select [V] Virtual LAN from the Main Menu. | ||
| Enter [T] Trunk Configuration. | ||
| At the next menu, enter [A] or [B] at the selection prompt, and press Return. | ||
| a. Select [D] Delete Allowed VLAN(s). b. Enter the appropriate VLAN number at the selection prompt in the next menu, and press Return. |
To view the list of allowed VLANs, select [V] List Allowed VLANs from the Trunk Configuration Menu.
To add a pruning-eligible VLAN, do the following:
| Step | Action | ||
|---|---|---|---|
| Select [V] Virtual LAN from the Main Menu. | ||
| Enter [T] Trunk Configuration. | ||
| At the next menu, enter [A] or [B] at the selection prompt, and press Return. | ||
| a. Enter [E] Add Pruning Eligible VLAN(s) at the selection prompt. b. Enter the appropriate VLAN number at the selection prompt in the next menu. The Trunk Configuration Menu reappears. |
To verify that you have added a pruning-eligible VLAN, select [T] Trunk Configuration, and view the contents of the display. To view additional VLAN information, select [F] List Pruning Eligible VLANs.
To delete a pruning-eligible VLAN, do the following:
| Step | Action | ||
|---|---|---|---|
| Select [V] Virtual LAN from the Main Menu. | ||
| Enter [T] Trunk Configuration. | ||
| At the next menu, enter [A] or [B] at the selection prompt, and press Return. | ||
| a. Select [C] Delete Pruning Eligible VLAN(s). b. Enter the appropriate VLAN number at the selection prompt in the next menu, and press Return. |
For more information about pruning, refer to the "Configuring VTP Pruning" section in this chapter.
You can use the Trunk Configuration Menu to display the following lists:
The VTP maintains VLAN configuration consistency throughout the network. VTP manages the addition, deletion, and modification of VLANs at the system level, automatically communicating this information to all the other switches in the network. In addition, VTP minimizes these possible configuration inconsistencies that can result in security violations:
A switch configured in VTP server mode advertises VLAN configuration to neighboring switches through its trunks and learns new VLAN configurations from those neighbors. Use the server mode to add or delete VLANs and to modify VLAN information by using either the VTP MIB, the CLI, or the console. For example, when you add a VLAN, VTP advertises the new VLAN, and both servers and clients prepare to receive traffic on their trunk ports.
After the switch automatically transitions to VTP client mode, it transmits advertisements and learns new information from advertisements. However, you cannot add, delete, or modify a VLAN through the MIB, the CLI, or the console. The VTP client does not maintain VLAN information in nonvolatile storage; when it starts, it learns the configuration by receiving advertisements from the trunk ports.
In VTP transparent mode, the switch does not advertise or learn VLAN configurations from the network. When a switch is in VTP transparent mode, you can modify, add, or delete VLANs through the console, the CLI, or the MIB.
Table 2-6 shows the maximum number of VLANs stored in nonvolatile RAM (NVRAM), the console or MIB configuration options, the advertisement options, and the maximum number of active VLANs for Catalyst 1900 and Catalyst 2820 switches.
| Mode | Maximum Number of VLANs in NVRAM | MIB, CLI, or Console Configuration | Switch Receives Advertisements | Maximum Number of VLANs |
|---|---|---|---|---|
VTP server | 128 | MIB, CLI, or console configuration for up to 128 VLANs | Yes | 128 |
VTP transparent | 128 | MIB, CLI, or console configuration for up to 128 VLANs | No | 128 |
VTP client | 0 | MIB, CLI, or console configuration | Yes | 1005 |
Using VTP, each Catalyst 1900 and 2820 switch advertises on its trunk ports its management domain, which defines the boundary of a specified VLAN, its configuration revision number, and its known VLANs and their specific parameters. A switch can reside in only one VTP management domain.
Through trunks, VTP servers transmit information to other switches and receive updates. VTP servers also maintain information, such as the list of VLANs in the VTP management domain in NVRAM.
VTP also dynamically maps VLANs across multiple LAN types, using unique names and internal index associations. VTP information is transmitted on all trunk connections, including ISL, IEEE 802.10, and LANE. The VTP MIB provides the SNMP instrumentation for the VTP, allowing the reading and setting of specific VTP parameters.
To configure VTP, do the following:
| Step | Action | ||
|---|---|---|---|
| Select [V] Virtual LAN from the Main Menu. | ||
| Access [N] Domain Name on the Virtual LAN Menu. Verify that the server has a VTP management domain so that VTP information can be sent to other VTP switches in the management domain. Press Return to view the Virtual Lan Menu. | ||
| Select [V] VTP Mode Control from the VLAN Configuration Menu. | ||
| Enter [S] Server at the selection prompt. The VLAN Configuration Menu reappears. |
To verify that VTP is enabled and the switch is transmitting and receiving advertisements, do the following:
| Step | Action | ||
|---|---|---|---|
| Select [V] Virtual LAN from the Main Menu. | ||
| Select [L] List VLANs from the Virtual LAN Menu. | ||
| Select [P] VTP Statistics at the selection prompt of the Virtual LAN Menu, and view the contents on the display. |
| Step | Action | ||
|---|---|---|---|
| Select [V] Virtual LAN from the Main Menu. | ||
| a. Select [W] VTP Password from the Virtual LAN Menu. b. Enter a password at the selection prompt. |
Refer to Figure 2-8 and Figure 2-9. The Catalyst 1900 and Catalyst 2820 switches are connected by trunks that also are spanning-tree forwarding paths.
In Figure 2-8, VTP pruning is not configured. The switch fabric consists of six Catalyst 1900 and Catalyst 2820 switches, shown as switches 1 through 6. Port 1 on switch 1 and port 2 on switch 4 are associated with the Red VLAN. The broadcast traffic from port 1 on switch 1 to port 2 on switch 4 is forwarded to all switches, even though switches 3, 5, and 6 have no ports on the Red VLAN.
Refer to Figure 2-9, in which VTP pruning is enabled.
In Figure 2-9, the broadcast traffic from port 1 on switch 1 to port 2 on switch 4 is not forwarded to switches 3, 5, and 6 because the traffic is pruned on the specified ports. Switches 3, 5, and 6 have no ports on the Red VLAN, and VTP pruning has reduced the flooding storm to switches not associated with the Red VLAN.
To enable VTP pruning, do the following:
| Step | Action | ||
|---|---|---|---|
| Select [V] Virtual LAN from the Main Menu. | ||
| Select [F] VTP Pruning Mode. | ||
| Enter Enable at the selection prompt. The VLAN Configuration Menu reappears. |
To verify that you have enabled VTP pruning, select [F] VTP Pruning Mode, and view the VTP pruning state.
You can monitor VTP by displaying its configuration information: the domain name, the current VTP revision, and the number of VLANs. You can also display statistics about the advertisements sent and received by the switch.
To monitor VTP activity, perform this task from the CLI privileged EXEC mode:
| Step | Action | ||
|---|---|---|---|
| show vtp | ||
| show vtp statistics |
This example shows how to display VTP configuration information:
hostname# show vtp
VTP version: 1
Configuration revision: 3
Maximum VLANs supported locally: 1005
Number of existing VLANs: 5
VTP domain name : Zorro
VTP password : vtp_server
VTP operating mode : Server
VTP pruning mode : Enabled
VTP traps generation : Enabled
Configuration last modified by: 10.1.126.45 at 9-4-99 00:12:24
This example shows how to display VTP messages and pruning statistics:
hostname# show vtp statistics
Receive Statistics Transmit Statistics
----------------------------------- -----------------------------------
Summary Adverts0Summary Adverts 0
Subset Adverts0Subset Adverts 0
Advert Requests0Advert Requests 0
Configuration Errors:
Revision Errors0
Digest Errors0
VTP Pruning Statistics:
Port Join Received Join Transmitted Summary Adverts received
with no pruning support
---- ------------- ---------------- ------------------------
A 0 0 0
B 0 0 0
You can move a connection from a port on one switch to a port on another switch in the network (without reconfiguring the port) by assigning dynamic ports to a VLAN.
To configure dynamic port VLAN membership, you must configure the Virtual LAN Membership Policy Server (VMPS) and assign ports on each switch with dynamic VLAN membership. Dynamic ports work in conjunction with the VMPS, which holds a database of MAC addresses-to-VLAN mappings. Catalyst 1900 and Catalyst 2820 switches do not function as VMPSs. The VMPS must be running on another device in the network, such as a Catalyst 5000 series switch.
The VMPS has a database of MAC-address-to-VLAN mappings that places the end station into the correct VLAN. You must configure the VMPS before configuring a port as dynamic. After you configure the VMPS, the configuration information is downloaded from a TFTP server, and the VMPS begins to accept requests from clients.
The switch queries the VMPS for the appropriate VLAN assignment by sending the VMPS the source MAC address of the incoming packet.
Upon receiving a valid request from a switch, the VMPS searches its database for a MAC address-to-VLAN mapping. Based on the request and the VMPS mode, the VMPS takes one of the following actions:
You can configure a fallback VLAN name on the VMPS. If the requested MAC address is not in the table, the VMPS sends the fallback VLAN name in response. If you do not configure a fallback VLAN and the MAC address is not in the table, the VMPS sends an access-denied response. If the VMPS is in secure mode, it sends a port-shutdown response.
You can also make an explicit entry in the configuration table to deny access to specific MAC addresses for security reasons by specifying a none keyword for the VLAN name. Again, the VMPS sends either an access-denied or port-shutdown response.
Before configuring dynamic ports, you must configure the VMPS so that it is active and accessible by the switch.
A dynamic port can belong to only one VLAN at a time. Upon link-up, a dynamic port is isolated from its static VLAN. The switch does not forward traffic to or from this port until a VLAN is identified for the port. Until a valid VLAN is assigned to a dynamic port, no connectivity is allowed. The source MAC address from the first packet of a new host on the dynamic port is sent to the VMPS. The VMPS provides the VLAN number to which this port must be assigned. For example, suppose the switch sends a valid query to the VMPS, and the VMPS response is "Place port in VLAN X." At this point, the host is connected to VLAN X through the switch fabric.
Multiple hosts (MAC addresses) can be active on a dynamic port if they are all in the same VLAN. Upon link-down, a dynamic port is returned to its initial state and is isolated from other VLANs. The switch detects only the first host that comes online through this port.
Dynamic port VLAN membership interacts with the following features:
| Step | Action | ||
|---|---|---|---|
| Select [V] Virtual LAN from the Main Menu. | ||
| a. Select [S] VLAN Membership Servers. b. Select [1] 1st VMPS IP Address. c. Enter the IP address of the server, and press Return. | ||
| a. Select [S] VLAN Membership Servers. b. Select [2], [3], or [4], enter the appropriate IP addresses, and press Return. | ||
| a. Select [S] VLAN Membership Servers. b. Select [P] Primary Server. c. Select the number of the server to be used as the primary VMPS. | ||
| Select [R] Number of retries before changing server, enter the appropriate number, and press Return. |
To verify that you have configured the VMPS addresses, access the VLAN Membership Servers Menu, and view the contents of this display.
After configuring the addresses of the VMPS, configure the ports as dynamic.
| Step | Action | ||
|---|---|---|---|
| Select [V] Virtual LAN from the Main Menu. | ||
| Select [E] VLAN Membership from the VLAN Configuration Menu. | ||
| Select [M] Membership Type from the VLAN Membership Menu. | ||
| Enter the port number at the selection prompt. | ||
| Select [D] Dynamic at the selection prompt. |
To verify that you have configured the port as a dynamic port, select [E] VLAN Membership to see the VLAN membership configuration display for all ports. The display shows a port status change from static to dynamic.
STP provides path redundancy while preventing undesirable loops that are caused by multiple active paths. For an Ethernet network to function properly, only one active path must exist between two stations.
Loops result in some switches seeing stations appear on both sides of the switch. This condition voids the forwarding algorithm and allows forwarding of duplicate frames.
STP defines a tree that spans all switches in an extended network and forces certain redundant data paths into a standby (blocked) state. If one of the network segments in the spanning tree becomes unreachable, or if STP costs change, the spanning-tree algorithm reconfigures the spanning-tree topology and reestablishes the link by activating the standby path. The STP operation is transparent to end stations, which do not recognize whether they are connected to a single LAN segment or to a switched LAN of multiple segments.
To access the Spanning Tree Configuration Menu, do the following:
| Step | Action | ||
|---|---|---|---|
| Select [N] Network Management from the Main Menu. | ||
| Enter [B] Bridge - Spanning Tree from the Network Management Menu. |
To enable or disable STP, do the following:
| Step | Action | ||
|---|---|---|---|
| Select [N] Network Management from the Main Menu. | ||
| Enter [B] Bridge - Spanning Tree from the Network Management Menu. | ||
| Enter [E] at the selection prompt, and press Return. | ||
| Enter [D] at the selection prompt, and press Return. |
To check the STP status of a VLAN, do the following:
| Step | Action | ||
|---|---|---|---|
| Select [N] Network Management from the Main Menu. | ||
| Enter [B] Bridge - Spanning Tree from the Network Management Menu. | ||
| Select [O] VLAN Bridge Operating Parameters. | ||
| Enter the VLAN number at the selection prompt. Press Return. |
The following VLAN STP operating parameters are displayed:
The Enterprise Edition software contains four configuration options for VLANs enabled with STP. For each option, you can configure a unique bridge priority, max age, hello time, and forward delay. After configuring an option, you can assign it to one STP instance or to several STP instances. By default, option 1 is assigned to all STP instances.
For more information about the bridge priority, max age, hello time, and forward delay options, refer to the Catalyst 1900 Series Installation and Configuration Guide or the Catalyst 2820 Series Installation and Configuration Guide.
To configure bridge priority, max age, hello time, and forward delay, do the following:
| Step | Action | ||
|---|---|---|---|
| Enter [N] Network Management at the selection prompt in the Main Menu. | ||
| Enter [B] Bridge - Spanning Tree from the Network Management Menu. | ||
| At the selection prompt, enter [1], [2], [3], or [4] to access the option screen. | ||
| Enter [B] Bridge Priority at the selection prompt, and enter the Bridge Priority value. | ||
| Enter [M] Max Age at the selection prompt, and enter the Max Age value. | ||
| Enter [H] Hello Time at the selection prompt, and enter the Hello Time value. | ||
| Enter [F] Forward Delay at the selection prompt, and enter the Forward Delay value. | ||
| Enter [N] Next Option at the selection prompt to access another option. |
To assign an STP instance to a specific option, do the following:
| Step | Action | ||
|---|---|---|---|
| Enter [N] Network Management at the selection prompt in the Main Menu. | ||
| Enter [B] Bridge - Spanning Tree from the Network Management Menu. | ||
| a. Enter option 1, 2, 3, or 4 at the selection prompt. b. Select [A] Assign VLANs to option. c. Enter the VLAN number at the selection prompt, and press Return. You see the spanning-tree option menu. d. Select [X] Exit to the Bridge STP Configuration Menu. |
Posted: Thu Oct 28 20:10:05 PDT 1999
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