Software Configuration Guide (4.5)
Configuring VLAN Trunks on Fast Ethernet and Gigabit Ethernet Ports
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Table Of Contents

Configuring VLAN Trunks on Fast Ethernet and Gigabit Ethernet Ports

Understanding How VLAN Trunks Work

Trunking Overview

Trunking Modes and Encapsulation Types

Trunking Support

IEEE 802.1Q Trunk Restrictions

Default Trunk Configuration

Configuring a Trunk Link

Configuring an ISL Trunk

Configuring an IEEE 802.1Q Trunk

Configuring an ISL/802.1Q Negotiating Trunk Port

Defining the Allowed VLANs on a Trunk

Disabling a Trunk Port

Example VLAN Trunk Configurations

ISL Trunk Configuration Example

Load-Sharing VLAN Traffic Over Parallel Trunks Example

IEEE 802.1Q nonegotiate Trunk Configuration Example


Configuring VLAN Trunks on Fast Ethernet and Gigabit Ethernet Ports

This chapter describes how to configure Fast Ethernet and Gigabit Ethernet virtual LAN (VLAN) trunks.

Note   For complete information on configuring VLANs, refer to "."

Note   For complete syntax and usage information for the commands used in this chapter, refer to the Command Reference for your switch.

This chapter consists of these sections:

•Understanding How VLAN Trunks Work

•Default Trunk Configuration

•Configuring a Trunk Link

•Example VLAN Trunk Configurations

Understanding How VLAN Trunks Work

These sections describe how VLAN trunks work on the Catalyst 5000, 4000, 2948G, 2926G, and 2926 series switches:

•Trunking Overview

•Trunking Modes and Encapsulation Types

•IEEE 802.1Q Trunk Restrictions

Trunking Overview

A trunk is a point-to-point link between one or more switch ports and another networking device such as a router or a switch. Trunks carry the traffic of multiple VLANs over a single link and allow you to extend VLANs across an entire network.

Two trunking encapsulations are available on Fast Ethernet and Gigabit Ethernet ports:

•InterSwitch Link (ISL)—ISL is a Cisco-proprietary trunking encapsulation

•IEEE 802.1Q—802.1Q is an industry-standard trunking encapsulation

Note   Trunking capabilities are hardware-dependent. For example, the Catalyst 4000 series switch modules support only 802.1Q encapsulation. To determine whether your hardware supports trunking, and to determine which trunking encapsulations are supported, see your hardware documentation or use the show port capabilities command.

You can configure a trunk on a single Fast or Gigabit Ethernet port or on a Fast or Gigabit EtherChannel bundle. For more information about Fast and Gigabit EtherChannel, see "."

Fast Ethernet and Gigabit Ethernet trunk ports support five different trunking modes (see ). In addition, on certain Fast Ethernet and Gigabit Ethernet ports you can specify whether the trunk will use ISL encapsulation, 802.1Q encapsulation, or whether the encapsulation type will be autonegotiated.

Trunk negotiation is managed by the Dynamic Trunking Protocol (DTP) in supervisor engine software release 4.2 and later. DTP supports autonegotiation of both ISL and IEEE 802.1Q trunks. In prior releases, trunk negotiation is managed by the Dynamic Inter-Switch Link (DISL) protocol. DISL supports autonegotiation of ISL trunks only. In supervisor engine software release 4.1, you must manually configure IEEE 802.1Q trunks on both ends of the link. IEEE 802.1Q trunks are not supported prior to software release 4.1.

Trunking Modes and Encapsulation Types

lists the trunking modes used with the set trunk command and describes how they function on Fast Ethernet and Gigabit Ethernet ports. lists the encapsulation types used with the set trunk command and describes how they function on Fast Ethernet and Gigabit Ethernet ports. You can use the show port capabilities command to determine which encapsulation types a particular port supports.

Table 11-1 Fast Ethernet and Gigabit Ethernet Trunking Modes

Mode
Function

on

Puts the port into permanent trunking mode and negotiates to convert the link into a trunk link. The port becomes a trunk port even if the neighboring port does not agree to the change.

off

Puts the port into permanent nontrunking mode and negotiates to convert the link into a nontrunk link. The port becomes a nontrunk port even if the neighboring port does not agree to the change.

desirable

Makes the port actively attempt to convert the link to a trunk link. The port becomes a trunk port if the neighboring port is set to on, desirable, or auto mode.

auto

Makes the port willing to convert the link to a trunk link. The port becomes a trunk port if the neighboring port is set to on or desirable mode. This is the default mode for Fast and Gigabit Ethernet ports.

nonegotiate

Puts the port into permanent trunking mode but prevents the port from generating DTP frames. You must configure the neighboring port manually as a trunk port to establish a trunk link.


Table 11-2 Fast Ethernet and Gigabit Ethernet Trunk Encapsulation Types

Encapsulation
Function

isl

Specifies ISL encapsulation on the trunk link.

dot1q

Specifies IEEE 802.1Q encapsulation on the trunk link. IEEE 802.1Q trunks are supported in Catalyst 5000 series software release 4.1 and later with 802.1Q-capable hardware. Automatic negotiation of 802.1Q trunks is supported in software release 4.2 and later.

negotiate

Specifies that the port negotiate with the neighboring port to become an ISL (preferred) or 802.1Q trunk, depending on the configuration and capabilities of the neighboring port. This keyword is available in software release 4.2 and later.


The trunking mode, the trunk encapsulation type, and the hardware capabilities of the two connected ports determine whether a trunk link comes up and the type of trunk the link becomes. shows the result of the possible trunking configurations.

Table 11-3 Results of Possible Fast Ethernet and Gigabit Ethernet Trunk Configurations 

Neighbor Port Trunk Mode and Trunk Encapsulation
Local Port Trunk Mode and Trunk Encapsulation
off
isl or dot1q
on
isl
desirable
isl
auto
isl
on
dot1q
desirable
dot1q
auto
dot1q
desirable
negotiate
auto
negotiate

off
isl or dot1q

Local:
Nontrunk

Neighbor:
Nontrunk

Local:
ISL trunk

Neighbor:
Nontrunk

Local:
Nontrunk

Neighbor:
Nontrunk

Local:
Nontrunk

Neighbor:
Nontrunk

Local:
1Q trunk

Neighbor:
Nontrunk

Local:
Nontrunk

Neighbor:
Nontrunk

Local:
Nontrunk

Neighbor:
Nontrunk

Local:
Nontrunk

Neighbor:
Nontrunk

Local:
Nontrunk

Neighbor:
Nontrunk

on
isl

Local:
Nontrunk

Neighbor:
ISL trunk

Local:
ISL trunk

Neighbor:
ISL trunk

Local:
ISL trunk

Neighbor:
ISL trunk

Local:
ISL trunk

Neighbor:
ISL trunk

Local:
1Q trunk1

Neighbor:
ISL trunk1

Local:
Nontrunk

Neighbor:
ISL trunk

Local:
Nontrunk

Neighbor:
ISL trunk

Local:
ISL trunk

Neighbor:
ISL trunk

Local:
ISL trunk

Neighbor:
ISL trunk

desirable
isl

Local:
Nontrunk

Neighbor:
Nontrunk

Local:
ISL trunk

Neighbor:
ISL trunk

Local:
ISL trunk

Neighbor:
ISL trunk

Local:
ISL trunk

Neighbor:
ISL trunk

Local:
1Q trunk

Neighbor:
Nontrunk

Local:
Nontrunk

Neighbor:
Nontrunk

Local:
Nontrunk

Neighbor:
Nontrunk

Local:
ISL trunk

Neighbor:
ISL trunk

Local:
ISL trunk

Neighbor:
ISL trunk

auto
isl

Local:
Nontrunk

Neighbor:
Nontrunk

Local:
ISL trunk

Neighbor:
ISL trunk

Local:
ISL trunk

Neighbor:
ISL trunk

Local:
Nontrunk

Neighbor:
Nontrunk

Local:
1Q trunk

Neighbor:
Nontrunk

Local:
Nontrunk

Neighbor:
Nontrunk

Local:
Nontrunk

Neighbor:
Nontrunk

Local:
ISL trunk

Neighbor:
ISL trunk

Local:
Nontrunk

Neighbor:
Nontrunk

on
dot1q

Local:
Nontrunk

Neighbor:
1Q trunk

Local:
ISL trunk1

Neighbor:
1Q trunk1

Local:
Nontrunk

Neighbor:
1Q trunk

Local:
Nontrunk

Neighbor:
1Q trunk

Local:
1Q trunk

Neighbor:
1Q trunk

Local:
1Q trunk

Neighbor:
1Q trunk

Local:
1Q trunk

Neighbor:
1Q trunk

Local:
1Q trunk

Neighbor:
1Q trunk

Local:
1Q trunk

Neighbor:
1Q trunk

desirable
dot1q

Local:
Nontrunk

Neighbor:
Nontrunk

Local:
ISL trunk

Neighbor:
Nontrunk

Local:
Nontrunk

Neighbor:
Nontrunk

Local:
Nontrunk

Neighbor:
Nontrunk

Local:
1Q trunk

Neighbor:
1Q trunk

Local:
1Q trunk

Neighbor:
1Q trunk

Local:
1Q trunk

Neighbor:
1Q trunk

Local:
1Q trunk

Neighbor:
1Q trunk

Local:
1Q trunk

Neighbor:
1Q trunk

auto
dot1q

Local:
Nontrunk

Neighbor:
Nontrunk

Local:
ISL trunk

Neighbor:
Nontrunk

Local:
Nontrunk

Neighbor:
Nontrunk

Local:
Nontrunk

Neighbor:
Nontrunk

Local:
1Q trunk

Neighbor:
1Q trunk

Local:
1Q trunk

Neighbor:
1Q trunk

Local:
Nontrunk

Neighbor:
Nontrunk

Local:
1Q trunk

Neighbor:
1Q trunk

Local:
Nontrunk

Neighbor:
Nontrunk

desirable negotiate

Local:
Nontrunk

Neighbor:
Nontrunk

Local:
ISL trunk

Neighbor:
ISL trunk

Local:
ISL trunk

Neighbor:
ISL trunk

Local:
ISL trunk

Neighbor:
ISL trunk

Local:
1Q trunk

Neighbor:
1Q trunk

Local:
1Q trunk

Neighbor:
1Q trunk

Local:
1Q trunk

Neighbor:
1Q trunk

Local:
ISL trunk

Neighbor:
ISL trunk

Local:
ISL trunk

Neighbor:
ISL trunk

auto
negotiate

Local:
Nontrunk

Neighbor:
Nontrunk

Local:
ISL trunk

Neighbor:
ISL trunk

Local:
ISL trunk

Neighbor:
ISL trunk

Local:
Nontrunk

Neighbor:
Nontrunk

Local:
1Q trunk

Neighbor:
1Q trunk

Local:
1Q trunk

Neighbor:
1Q trunk

Local:
Nontrunk

Neighbor:
Nontrunk

Local:
ISL trunk

Neighbor:
ISL trunk

Local:
Nontrunk

Neighbor:
Nontrunk

1 Using this configuration can result in spanning-tree loops and is not recommended.


Note   DTP is a point-to-point protocol. However, some internetworking devices might forward DTP frames improperly. To avoid this problem, ensure that trunking is turned off on ports connected to non-switch devices if you do not intend to trunk across those links. When manually enabling trunking on a link to a Cisco router, use the nonegotiate keyword to cause the port to become a trunk but not generate DTP frames. The nonegotiate keyword is available in supervisor engine software release 2.4(3) and later.

Trunking Support

Trunking capabilities are hardware-dependent. shows which switches have available hardware that supports the two trunking encapsulations. To determine whether a specific piece of hardware supports trunking, and to determine which trunking encapsulations are supported, see your hardware documentation or use the show port capabilities command.

Table 11-4 Trunking Encapsulation Support

Trunking Method
Catalyst 5000 Series
Catalyst 4000 Series
Catalyst 2948G Series
Catalyst 2926G Series
Catalyst 2926 Series

ISL

Yes

No

No

Yes

Yes

IEEE 802.1Q

Yes

Yes

Yes

Yes

No


IEEE 802.1Q Trunk Restrictions

IEEE 802.1Q trunks impose some limitations on the trunking strategy for a network. The following restrictions apply when using 802.1Q trunks:

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

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

•Make sure the native VLAN for an 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 802.1Q trunk, or disable spanning tree on every VLAN in the network. Make sure your network is loop-free before disabling spanning tree.

Default Trunk Configuration

shows the default Fast Ethernet and Gigabit Ethernet trunk configuration.

Table 11-5 Default Fast Ethernet and Gigabit Ethernet Trunk Configuration

Feature
Default Configuration

Trunk mode

auto

Trunk encapsulation

•negotiate (on hardware supporting both ISL and 802.1Q)

•isl (on hardware supporting ISL only)

•dot1q (on hardware supporting 802.1Q only)

Allowed VLAN range

VLANs 1-1005


Configuring a Trunk Link

These sections describe how to configure a trunk link on Fast Ethernet and Gigabit Ethernet ports and how to define the allowed VLAN range on a trunk:

•Configuring an ISL Trunk

•Configuring an IEEE 802.1Q Trunk

•Configuring an ISL/802.1Q Negotiating Trunk Port

•Defining the Allowed VLANs on a Trunk

•Disabling a Trunk Port

Configuring an ISL Trunk

Note   Some hardware does not support ISL encapsulation. To determine whether your hardware supports ISL, see your hardware documentation or use the show port capabilities command.

To configure an ISL trunk, perform this task in privileged mode:

Task
Command

Step 1 Configure an ISL trunk.

set trunk mod_num/port_num [on | desirable | auto | nonegotiate] isl

Step 2 Verify the trunking configuration.

show trunk [mod_num/port_num]


This example shows how to configure a port as a trunk and how to verify the trunk configuration. This example assumes that the neighbor port is in auto mode. 

Console> (enable) set trunk 1/1 on

Port(s) 1/1 trunk mode set to on.

Console> (enable) 06/16/1998,22:16:39:DTP-5:Port 1/1 has become isl trunk

06/16/1998,22:16:40:PAGP-5:Port 1/1 left bridge port 1/1.

06/16/1998,22:16:40:PAGP-5:Port 1/1 joined bridge port 1/1.

Console> (enable) show trunk

Port      Mode         Encapsulation  Status        Native vlan

--------  -----------  -------------  ------------  -----------

 1/1      on           isl            trunking      1

Port      Vlans allowed on trunk

--------  ---------------------------------------------------------------------

 1/1      1-1005

Port      Vlans allowed and active in management domain 

--------  ---------------------------------------------------------------------

 1/1      1,521-524

Port      Vlans in spanning tree forwarding state and not pruned

--------  ---------------------------------------------------------------------

 1/1      

Console> (enable)

This example shows how to place a port in desirable mode and how to verify the trunk configuration. This example assumes that the neighbor port is in auto mode. 

Console> (enable) set trunk 1/2 desirable

Port(s) 1/2 trunk mode set to desirable.

Console> (enable) 06/16/1998,22:20:16:DTP-5:Port 1/2 has become isl trunk

06/16/1998,22:20:16:PAGP-5:Port 1/2 left bridge port 1/2.

06/16/1998,22:20:16:PAGP-5:Port 1/2 joined bridge port 1/2.

Console> (enable) show trunk 1/2

Port      Mode         Encapsulation  Status        Native vlan

--------  -----------  -------------  ------------  -----------

 1/2      desirable    isl            trunking      1

Port      Vlans allowed on trunk

--------  ---------------------------------------------------------------------

 1/2      1-1005

Port      Vlans allowed and active in management domain 

--------  ---------------------------------------------------------------------

 1/2      1,521-524

Port      Vlans in spanning tree forwarding state and not pruned

--------  ---------------------------------------------------------------------

 1/2      

Console> (enable)

Configuring an IEEE 802.1Q Trunk

Note   Some hardware does not support 802.1Q encapsulation. To determine whether your hardware supports 802.1Q, see your hardware documentation or use the show port capabilities command.

Note   IEEE 802.1Q trunks require supervisor engine software release 4.1 or later and 802.1Q-capable hardware. In release 4.1, only the nonegotiate and off modes function with 802.1Q trunks. Autonegotiation of 802.1Q trunks is supported in software release 4.2 and later.

Caution   
DTP (formerly known as DISL) negotiation does not occur on IEEE 802.1Q trunks in software releases prior to release 4.2. You must configure the ports on both ends of the trunk link as 802.1Q trunks using the set trunk command with the nonegotiate and dot1q keywords. Expect Spanning-Tree Protocol (STP) to block the port on the other end of the trunk link until you configure that end of the link as an 802.1Q trunk as well. Do not configure one end of a trunk as an 802.1Q trunk and the other end as an ISL trunk or a nontrunk port. Errors will occur and no traffic can pass over the link. For more information, see the "Trunking Modes and Encapsulation Types" section.

To configure an IEEE 802.1Q trunk, perform this task in privileged mode:

Task
Command

Step 1 Configure an 802.1Q trunk.

set trunk mod_num/port_num [on | desirable | auto | nonegotiate] dot1q

Step 2 Verify the trunking configuration.

show trunk [mod_num/port_num]


This example shows how to configure an IEEE 802.1Q trunk and how to verify the trunk configuration in software release 4.2 and later: 

Console> (enable) set trunk 2/9 desirable dot1q

Port(s) 2/9 trunk mode set to desirable.

Port(s) 2/9 trunk type set to dot1q.

Console> (enable) 07/02/1998,18:22:25:DTP-5:Port 2/9 has become dot1q trunk


Console> (enable) show trunk 

Port      Mode         Encapsulation  Status        Native vlan

--------  -----------  -------------  ------------  -----------

 2/9      desirable    dot1q          trunking      1


Port      Vlans allowed on trunk

--------  ---------------------------------------------------------------------

 2/9      1-1005


Port      Vlans allowed and active in management domain 

--------  ---------------------------------------------------------------------

 2/9      1,5,10-32,101-120,150,200,250,300,400,500,600,700,800,900,1000


Port      Vlans in spanning tree forwarding state and not pruned

--------  ---------------------------------------------------------------------

 2/9      5,10-32,101-120,150,200,250,300,400,500,600,700,800,900,1000

Console> (enable)

This example shows how to configure an IEEE 802.1Q trunk in software release 4.1: 

Console> (enable) set trunk 4/5 nonegotiate dot1q

Port(s) 4/5 trunk mode set to nonegotiate.

Port(s) 4/5 trunk type set to dot1q.

Console> (enable) 2/20/1998,23:38:35:DISL-5:Port 1/1 has become dot1q trunk

Configuring an ISL/802.1Q Negotiating Trunk Port

To configure a trunk port to negotiate the trunk encapsulation type (either ISL or IEEE 802.1Q), perform this task in privileged mode:

Task
Command

Step 1 Configure a port to negotiate the trunk encapsulation type.

set trunk mod_num/port_num [on | desirable | auto | nonegotiate] negotiate

Step 2 Verify the trunking configuration.

show trunk [mod_num/port_num]


This example shows how to configure a port to negotiate the encapsulation type and how to verify the trunk configuration. This example assumes that the neighbor port is in auto mode with encapsulation set to isl or negotiate. 

Console> (enable) set trunk 4/11 desirable negotiate

Port(s) 4/11 trunk mode set to desirable.

Port(s) 4/11 trunk type set to negotiate.

Console> (enable)

Console> (enable) show trunk 4/11

Port      Mode         Encapsulation  Status        Native vlan

--------  -----------  -------------  ------------  -----------

 4/11     desirable    n-isl          trunking      1

Port      Vlans allowed on trunk

--------  ---------------------------------------------------------------------

 4/11     1-1005

Port      Vlans allowed and active in management domain 

--------  ---------------------------------------------------------------------

 4/11     1,5,10-32,55,101-120,998-1000

Port      Vlans in spanning tree forwarding state and not pruned

--------  ---------------------------------------------------------------------

 4/11     1,5,10-32,55,101-120,998-1000

Console> (enable)

Defining the Allowed VLANs on a Trunk

When you configure a trunk port, all VLANs are added to the allowed VLANs list for that trunk. However, you can remove VLANs from the allowed list to prevent traffic for those VLANs from passing over the trunk. You cannot remove VLAN 1, the default VLAN, from the allowed list.

Note   When you first configure a port as a trunk, the set trunk command always adds all VLANs to the allowed VLAN list for the trunk, even if you specify a VLAN range (any specified VLAN range is ignored). To modify the allowed VLANs list, use a combination of the clear trunk and set trunk commands to specify the allowed VLANs.

To define the allowed VLAN list for a trunk port, perform this task in privileged mode:

Task
Command

Step 1 Remove VLANs from the allowed VLANs list for a trunk.

clear trunk mod_num/port_num vlans

Step 2 (Optional) Add specific VLANs to the allowed VLANs list for a trunk.

set trunk mod_num/port_num vlans

Step 3 Verify the allowed VLAN list for the trunk.

show trunk [mod_num/port_num]


This example shows how to define the allowed VLANs list for trunk port 1/1 to allow VLANs 1-100, VLAN 250, and VLANs 500-1005, and how to verify the allowed VLAN list for the trunk: 

Console> (enable) clear trunk 1/1 101-499

Removing Vlan(s) 101-499 from allowed list.

Port 1/1 allowed vlans modified to 1-100,500-1005.

Console> (enable) set trunk 1/1 250

Adding vlans 250 to allowed list.

Port(s) 1/1 allowed vlans modified to 1-100,250,500-1005.

Console> (enable) show trunk 1/1

Port      Mode         Encapsulation  Status        Native vlan

--------  -----------  -------------  ------------  -----------

 1/1      desirable    isl            trunking      1

Port      Vlans allowed on trunk

--------  ---------------------------------------------------------------------

 1/1      1-100,250,500-1005

Port      Vlans allowed and active in management domain

--------  ---------------------------------------------------------------------

 1/1      1,521-524

Port      Vlans in spanning tree forwarding state and not pruned

--------  ---------------------------------------------------------------------

 1/1      1,521-524

Console> (enable)

Disabling a Trunk Port

To explicitly turn off trunking on a port, perform this task in privileged mode:

Task
Command

Step 1 Turn off trunking on a port.

set trunk mod_num/port_num off

Step 2 Verify the trunking configuration.

show trunk [mod_num/port_num]


To return a port to the default trunk type and mode for that port type, perform this task in privileged mode:

Task
Command

Step 1 Return the port to the default trunking type and mode for that port type.

clear trunk mod_num/port_num

Step 2 Verify the trunking configuration.

show trunk [mod_num/port_num]


Example VLAN Trunk Configurations

This section contains example VLAN trunk configurations.

•ISL Trunk Configuration Example

•Load-Sharing VLAN Traffic Over Parallel Trunks Example

•IEEE 802.1Q nonegotiate Trunk Configuration Example

ISL Trunk Configuration Example

This example configuration shows how to configure an ISL trunk between two switches and how to limit the allowed VLANs on the trunk to VLAN 1 and VLANs 520-530.

In this example, port 1/1 (a Catalyst 5000 series supervisor engine Fast Ethernet uplink port) on Switch 1 is connected to a Fast Ethernet port on another switch. Both ports are in their default state, with the trunk mode set to auto (for more information, see the "Default Trunk Configuration" section).

Step 1 Enter the set trunk command to configure port 1/1 on Switch 1 as an ISL trunk port. By specifying the desirable keyword, the trunk is automatically negotiated with the neighboring port (port 1/2 on Switch 2). ISL encapsulation is assumed based on the hardware type. 

Switch1> (enable) set trunk 1/1 desirable

Port(s) 1/1 trunk mode set to desirable.

Switch1> (enable) 06/18/1998,12:20:23:DTP-5:Port 1/1 has become isl trunk

06/18/1998,12:20:23:PAGP-5:Port 1/1 left bridge port 1/1.

06/18/1998,12:20:23:PAGP-5:Port 1/1 joined bridge port 1/1.

Switch1> (enable)

Step 2 Enter the show trunk command to check the configuration. The Status field in the screen output indicates that port 1/1 is trunking. 

Switch1> (enable) show trunk 1/1

Port      Mode         Encapsulation  Status        Native vlan

--------  -----------  -------------  ------------  -----------

 1/1      desirable    isl            trunking      1

Port      Vlans allowed on trunk

--------  ---------------------------------------------------------------------

 1/1      1-1005

Port      Vlans allowed and active in management domain 

--------  ---------------------------------------------------------------------

 1/1      1,521-524

Port      Vlans in spanning tree forwarding state and not pruned

--------  ---------------------------------------------------------------------

 1/1      

Switch1> (enable)

Step 3 To define the allowed VLAN list for the trunk, use the clear trunk command to remove the VLANs that should not pass traffic over the trunk link. 

Switch1> (enable) clear trunk 1/1 2-519

Removing Vlan(s) 2-519 from allowed list.

Port 1/1 allowed vlans modified to 1,520-1005.

Switch1> (enable) clear trunk 1/1 531-1005

Removing Vlan(s) 531-1005 from allowed list.

Port 1/1 allowed vlans modified to 1,520-530.

Switch1> (enable) show trunk 1/1

Port      Mode         Encapsulation  Status        Native vlan

--------  -----------  -------------  ------------  -----------

 1/1      desirable    isl            trunking      1

Port      Vlans allowed on trunk

--------  ---------------------------------------------------------------------

 1/1      1,520-530

Port      Vlans allowed and active in management domain 

--------  ---------------------------------------------------------------------

 1/1      1,521-524

Port      Vlans in spanning tree forwarding state and not pruned

--------  ---------------------------------------------------------------------

 1/1      1,521-524

Switch1> (enable)

Step 4 Verify connectivity across the trunk using the ping command: 

Switch1> (enable) ping switch2

switch2 is alive

Switch1> (enable)

Load-Sharing VLAN Traffic Over Parallel Trunks Example

Using spanning-tree port-VLAN priorities, you can load-share VLAN traffic over parallel trunk ports so that traffic from some VLANs travels over one trunk, while traffic from other VLANs travels over the other trunk. This configuration allows traffic to be carried over both trunks simultaneously (instead of keeping one trunk in blocking mode), which reduces the total traffic carried over each trunk while still maintaining a fault-tolerant configuration.

Figure 11-1 shows a parallel trunk configuration between two switches, using the Fast Ethernet uplink ports on the supervisor engine.

Figure 11-1 Parallel Trunk Configuration Before Configuring VLAN-Traffic Load Sharing

By default, the port-VLAN priority for both trunks is equal (a value of 32). Therefore, STP blocks port 1/2 (Trunk 2) for each VLAN on Switch 1 to prevent forwarding loops. Trunk 2 is not used to forward traffic unless Trunk 1 fails.

This example shows how to configure the switches so that traffic from multiple VLANs is load-balanced over the parallel trunks.

Step 1 Configure a VTP domain on both Switch 1 and Switch 2 (by entering the set vtp command) so that the VLAN information configured on Switch 1 is learned by Switch 2. Make sure Switch 1 is a VTP server. You can configure Switch 2 as a VTP client or as a VTP server: 

Switch_1> (enable) set vtp domain BigCorp mode server

VTP domain BigCorp modified

Switch_1> (enable)


Switch_2> (enable) set vtp domain BigCorp mode server

VTP domain BigCorp modified

Switch_2> (enable)

Step 2 Create the VLANs on Switch 1 by entering the set vlan command. In this example, you see VLANs 10, 20, 30, 40, 50, and 60, as follows: 

Switch_1> (enable) set vlan 10

Vlan 10 configuration successful

Switch_1> (enable) set vlan 20

Vlan 20 configuration successful

Switch_1> (enable) set vlan 30

Vlan 30 configuration successful

Switch_1> (enable) set vlan 40

Vlan 40 configuration successful

Switch_1> (enable) set vlan 50

Vlan 50 configuration successful

Switch_1> (enable) set vlan 60

Vlan 60 configuration successful

Switch_1> (enable)

Step 3 Verify the VTP and VLAN configuration on Switch 1 by entering the show vtp domain and show vlan commands as follows: 

Switch_1> (enable) show vtp domain

Domain Name                      Domain Index VTP Version Local Mode  Password

-------------------------------- ------------ ----------- ----------- ----------

BigCorp                          1            2           server      -


Vlan-count Max-vlan-storage Config Revision Notifications

---------- ---------------- --------------- -------------

11         1023             13              disabled


Last Updater    V2 Mode  Pruning  PruneEligible on Vlans

--------------- -------- -------- -------------------------

172.20.52.10    disabled enabled  2-1000

Switch_1> (enable) show vlan

VLAN Name                             Status    Mod/Ports, Vlans

---- -------------------------------- --------- ----------------------------

1    default                          active    1/1-2

                                                2/1-12

                                                5/1-2

10   VLAN0010                         active

20   VLAN0020                         active

30   VLAN0030                         active

40   VLAN0040                         active

50   VLAN0050                         active

60   VLAN0060                         active

1002 fddi-default                     active

1003 token-ring-default               active

1004 fddinet-default                  active

1005 trnet-default                    active


<...output truncated...>


Switch_1> (enable)

Step 4 Configure the supervisor engine uplinks on Switch 1 as ISL trunk ports by entering the set trunk command. Specifying the desirable mode on the Switch 1 ports causes the ports on Switch 2 to negotiate to become trunk links (assuming that the Switch 2 uplinks are in the default auto mode). 

Switch_1> (enable) set trunk 1/1 desirable

Port(s) 1/1 trunk mode set to desirable.

Switch_1> (enable) 04/21/1998,03:05:05:DISL-5:Port 1/1 has become isl trunk


Switch_1> (enable) set trunk 1/2 desirable

Port(s) 1/2 trunk mode set to desirable.

Switch_1> (enable) 04/21/1998,03:05:13:DISL-5:Port 1/2 has become isl trunk

Step 5 Verify that the trunk links are up by entering the show trunk command as follows: 

Switch_1> (enable) show trunk 1

Port      Mode         Encapsulation  Status        Native vlan

--------  -----------  -------------  ------------  -----------

 1/1      desirable    isl            trunking      1

 1/2      desirable    isl            trunking      1


Port      Vlans allowed on trunk

--------  ---------------------------------------------------------------------

 1/1      1-1005

 1/2      1-1005


Port      Vlans allowed and active in management domain

--------  ---------------------------------------------------------------------

 1/1      1,10,20,30,40,50,60

 1/2      1,10,20,30,40,50,60


Port      Vlans in spanning tree forwarding state and not pruned

--------  ---------------------------------------------------------------------

 1/1

 1/2

Switch_1> (enable)

Step 6 Note that when the trunk links come up, VTP passes the VTP and VLAN configuration to Switch 2. Verify that Switch 2 has learned the VLAN configuration by entering the show vlan command on Switch 2: 

Switch_2> (enable) show vlan

VLAN Name                             Status    Mod/Ports, Vlans

---- -------------------------------- --------- ----------------------------

1    default                          active

10   VLAN0010                         active

20   VLAN0020                         active

30   VLAN0030                         active

40   VLAN0040                         active

50   VLAN0050                         active

60   VLAN0060                         active

1002 fddi-default                     active

1003 token-ring-default               active

1004 fddinet-default                  active

1005 trnet-default                    active


<...output truncated...>


Switch_2> (enable)

Step 7 Note that spanning tree takes one to two minutes to converge. Once the network stabilizes, check the spanning-tree state of each trunk port on Switch 1 by entering the show spantree command.

Trunk 1 is forwarding for all VLANs. Trunk 2 is blocking for all VLANs. On Switch 2, both trunks are forwarding for all VLANs, but no traffic passes over Trunk 2 because port 1/2 on Switch 1 is blocking. 

Switch_1> (enable) show spantree 1/1

Port      Vlan  Port-State     Cost   Priority  Fast-Start  Group-method

--------- ----  -------------  -----  --------  ----------  ------------

 1/1      1     forwarding        19        32   disabled

 1/1      10    forwarding        19        32   disabled

 1/1      20    forwarding        19        32   disabled

 1/1      30    forwarding        19        32   disabled

 1/1      40    forwarding        19        32   disabled

 1/1      50    forwarding        19        32   disabled

 1/1      60    forwarding        19        32   disabled

 1/1      1003  not-connected     19        32   disabled

 1/1      1005  not-connected     19         4   disabled

Switch_1> (enable) show spantree 1/2

Port      Vlan  Port-State     Cost   Priority  Fast-Start  Group-method

--------- ----  -------------  -----  --------  ----------  ------------

 1/2      1     blocking          19        32   disabled

 1/2      10    blocking          19        32   disabled

 1/2      20    blocking          19        32   disabled

 1/2      30    blocking          19        32   disabled

 1/2      40    blocking          19        32   disabled

 1/2      50    blocking          19        32   disabled

 1/2      60    blocking          19        32   disabled

 1/2      1003  not-connected     19        32   disabled

 1/2      1005  not-connected     19         4   disabled

Switch_1> (enable)

Step 8 Divide the configured VLANs into two groups. You might want traffic from half of the VLANs to go over one trunk link and half over the other, or if one VLAN has heavier traffic than the others, you can have traffic from that VLAN go over one trunk and traffic from the other VLANs go over the other trunk link.

In this example, VLANs 10, 20, and 30 (Group 1) are forwarded over Trunk 1, and VLANs 40, 50, and 60 (Group 2) are forwarded over Trunk 2.

Step 9 On Switch 1, enter the set spantree portvlanpri command to change the port-VLAN priority for the Group 1 VLANs on Trunk 1 (port 1/1) to an integer value lower than the default of 32. 

Switch_1> (enable) set spantree portvlanpri 1/1 1 10

Port 1/1 vlans 1-9,11-1004 using portpri 32.

Port 1/1 vlans 10 using portpri 1.

Port 1/1 vlans 1005 using portpri 4.

Switch_1> (enable) set spantree portvlanpri 1/1 1 20

Port 1/1 vlans 1-9,11-19,21-1004 using portpri 32.

Port 1/1 vlans 10,20 using portpri 1.

Port 1/1 vlans 1005 using portpri 4.

Switch_1> (enable) set spantree portvlanpri 1/1 1 30

Port 1/1 vlans 1-9,11-19,21-29,31-1004 using portpri 32.

Port 1/1 vlans 10,20,30 using portpri 1.

Port 1/1 vlans 1005 using portpri 4.

Switch_1> (enable)

Step 10 On Switch 1, change the port-VLAN priority for the Group 2 VLANs on Trunk 2 (port 1/2) to an integer value lower than the default of 32. 

Switch_1> (enable) set spantree portvlanpri 1/2 1 40

Port 1/2 vlans 1-39,41-1004 using portpri 32.

Port 1/2 vlans 40 using portpri 1.

Port 1/2 vlans 1005 using portpri 4.

Switch_1> (enable) set spantree portvlanpri 1/2 1 50

Port 1/2 vlans 1-39,41-49,51-1004 using portpri 32.

Port 1/2 vlans 40,50 using portpri 1.

Port 1/2 vlans 1005 using portpri 4.

Switch_1> (enable) set spantree portvlanpri 1/2 1 60

Port 1/2 vlans 1-39,41-49,51-59,61-1004 using portpri 32.

Port 1/2 vlans 40,50,60 using portpri 1.

Port 1/2 vlans 1005 using portpri 4.

Switch_1> (enable)

Step 11 On Switch 2, change the port-VLAN priority for the Group 1 VLANs on Trunk 1 (port 1/1) to the same value you configured for those VLANs on Switch 1.
Caution   The port-VLAN priority for each VLAN must be equal on both ends of the link. 

Switch_2> (enable) set spantree portvlanpri 1/1 1 10

Port 1/1 vlans 1-9,11-1004 using portpri 32.

Port 1/1 vlans 10 using portpri 1.

Port 1/1 vlans 1005 using portpri 4.

Switch_2> (enable) set spantree portvlanpri 1/1 1 20

Port 1/1 vlans 1-9,11-19,21-1004 using portpri 32.

Port 1/1 vlans 10,20 using portpri 1.

Port 1/1 vlans 1005 using portpri 4.

Switch_2> (enable) set spantree portvlanpri 1/1 1 30

Port 1/1 vlans 1-9,11-19,21-29,31-1004 using portpri 32.

Port 1/1 vlans 10,20,30 using portpri 1.

Port 1/1 vlans 1005 using portpri 4.

Switch_2> (enable)

Step 12 On Switch 2, change the port-VLAN priority for the Group 2 VLANs on Trunk 2 (port 1/2) to the same value you configured for those VLANs on Switch 1. 

Switch_2> (enable) set spantree portvlanpri 1/2 1 40

Port 1/2 vlans 1-39,41-1004 using portpri 32.

Port 1/2 vlans 40 using portpri 1.

Port 1/2 vlans 1005 using portpri 4.

Switch_2> (enable) set spantree portvlanpri 1/2 1 50

Port 1/2 vlans 1-39,41-49,51-1004 using portpri 32.

Port 1/2 vlans 40,50 using portpri 1.

Port 1/2 vlans 1005 using portpri 4.

Switch_2> (enable) set spantree portvlanpri 1/2 1 60

Port 1/2 vlans 1-39,41-49,51-59,61-1004 using portpri 32.

Port 1/2 vlans 40,50,60 using portpri 1.

Port 1/2 vlans 1005 using portpri 4.

Switch_2> (enable)

Step 13 Note that when you have configured the port-VLAN priorities on both ends of the link, the spanning tree converges to use the new configuration.

Check the spanning-tree port states on Switch 1 by entering the show spantree command. The Group 1 VLANs should be forwarding on Trunk 1 and blocking on Trunk 2. The Group 2 VLANs should be blocking on Trunk 1 and forwarding on Trunk 2. 

Switch_1> (enable) show spantree 1/1

Port      Vlan  Port-State     Cost   Priority  Fast-Start  Group-method

--------- ----  -------------  -----  --------  ----------  ------------

 1/1      1     forwarding        19        32   disabled

 1/1      10    forwarding        19         1   disabled

 1/1      20    forwarding        19         1   disabled

 1/1      30    forwarding        19         1   disabled

 1/1      40    blocking          19        32   disabled

 1/1      50    blocking          19        32   disabled

 1/1      60    blocking          19        32   disabled

 1/1      1003  not-connected     19        32   disabled

 1/1      1005  not-connected     19         4   disabled

Switch_1> (enable) show spantree 1/2

Port      Vlan  Port-State     Cost   Priority  Fast-Start  Group-method

--------- ----  -------------  -----  --------  ----------  ------------

 1/2      1     blocking          19        32   disabled

 1/2      10    blocking          19        32   disabled

 1/2      20    blocking          19        32   disabled

 1/2      30    blocking          19        32   disabled

 1/2      40    forwarding        19         1   disabled

 1/2      50    forwarding        19         1   disabled

 1/2      60    forwarding        19         1   disabled

 1/2      1003  not-connected     19        32   disabled

 1/2      1005  not-connected     19         4   disabled

Switch_1> (enable)

Figure 11-2 shows the network after you configure VLAN traffic load-sharing.

Figure 11-2 Parallel Trunk Configuration After Configuring VLAN-Traffic Load Sharing

Figure 11-2 shows that both trunks are utilized when the network is operating normally and, if one trunk link fails, the other trunk link acts as an alternate forwarding path for the traffic previously traveling over the failed link.

If Trunk 1 fails in the network shown in Figure 11-2, STP reconverges to use Trunk 2 to forward traffic from all the VLANs, as shown in the following example: 

Switch_1> (enable) 04/21/1998,03:15:40:DISL-5:Port 1/1 has become non-trunk


Switch_1> (enable) show spantree 1/1

Port      Vlan  Port-State     Cost   Priority  Fast-Start  Group-method

--------- ----  -------------  -----  --------  ----------  ------------

 1/1      1     not-connected     19        32   disabled

Switch_1> (enable) show spantree 1/2

Port      Vlan  Port-State     Cost   Priority  Fast-Start  Group-method

--------- ----  -------------  -----  --------  ----------  ------------

 1/2      1     learning          19        32   disabled

 1/2      10    learning          19        32   disabled

 1/2      20    learning          19        32   disabled

 1/2      30    learning          19        32   disabled

 1/2      40    forwarding        19         1   disabled

 1/2      50    forwarding        19         1   disabled

 1/2      60    forwarding        19         1   disabled

 1/2      1003  not-connected     19        32   disabled

 1/2      1005  not-connected     19         4   disabled

Switch_1> (enable) show spantree 1/2

Port      Vlan  Port-State     Cost   Priority  Fast-Start  Group-method

--------- ----  -------------  -----  --------  ----------  ------------

 1/2      1     forwarding        19        32   disabled

 1/2      10    forwarding        19        32   disabled

 1/2      20    forwarding        19        32   disabled

 1/2      30    forwarding        19        32   disabled

 1/2      40    forwarding        19         1   disabled

 1/2      50    forwarding        19         1   disabled

 1/2      60    forwarding        19         1   disabled

 1/2      1003  not-connected     19        32   disabled

 1/2      1005  not-connected     19         4   disabled

Switch_1> (enable)

IEEE 802.1Q nonegotiate Trunk Configuration Example

This example configuration shows how to configure an IEEE 802.1Q Fast Ethernet trunk between two Catalyst 5000 series switches running software release 4.1 with 802.1Q-capable hardware. (Use the show port capabilities command or check the documentation for your hardware to see if your hardware is 802.1Q-capable.)

Note   The example in this section applies to IEEE 802.1Q configuration only in supervisor engine software release 4.1.

In software release 4.1, you must manually configure IEEE 802.1Q trunk ports on both ends of the link. IEEE 802.1Q trunks can be autonegotiated only in software release 4.2 and later. To properly configure an IEEE 802.1Q trunk in software release 4.1, the trunk type (encapsulation) and trunk mode must be the same on both ends of the link.

In this example, an 802.1Q trunk is configured between port 1/1 on Switch 1 and port 4/1 on Switch 2. The initial network configuration is shown in . Assume that the native VLAN is VLAN 1 on both ends of the link.

Figure 11-3 IEEE 802.1Q Trunking: Initial Network Configuration

Step 1 To configure a port as an 802.1Q trunk, enter the set trunk command. You must use the nonegotiate keyword when configuring a port as an 802.1Q trunk. 

Switch 1> (enable) set trunk 1/1 nonegotiate dot1q

Port(s) 1/1 trunk mode set to nonegotiate.

Port(s) 1/1 trunk type set to dot1q.

Switch 1> (enable) 04/15/1998,22:02:17:DISL-5:Port 1/1 has become dot1q trunk



Switch 2> (enable) 04/15/1998,22:01:42:SPANTREE-2: Rcved 1Q-BPDU on non-1Q-trunk 
port 4/1 vlan 1.

04/15/1998,22:01:42:SPANTREE-2: Block 4/1 on rcving vlan 1 for inc trunk port.

04/15/1998,22:01:42:SPANTREE-2: Block 4/1 on rcving vlan 1 for inc peer vlan 2.

Switch 2> (enable)

Notice that after the port on Switch 1 is configured as an 802.1Q trunk, syslog messages are displayed on the Switch 2 console, and port 4/1 on Switch 2 is blocked. STP blocks the port because there is a port-type inconsistency on the trunk link: port 1/1 on Switch 1 is configured as an 802.1Q trunk while port 4/1 on Switch 2 is configured as an ISL trunk (see ). Port 4/1 would also be blocked if it were configured as a nontrunk port.

Figure 11-4 IEEE 802.1Q Trunking: Port-Type Inconsistency

Step 2 Note that output from the show spantree and show spantree statistics commands on Switch 2 displays the problem. The configuration mismatch exists until the port on Switch 2 is properly configured. 

Switch 2> (enable) show spantree 1

VLAN 1

Spanning tree enabled

Spanning tree type          ieee


Designated Root             00-60-09-79-c3-00

Designated Root Priority    32768

Designated Root Cost        0

Designated Root Port        1/0

Root Max Age   20 sec    Hello Time 2  sec   Forward Delay 15 sec


Bridge ID MAC ADDR          00-60-09-79-c3-00

Bridge ID Priority          32768

Bridge Max Age 20 sec    Hello Time 2  sec   Forward Delay 15 sec


Port      Vlan  Port-State     Cost   Priority  Fast-Start  Group-method

--------- ----  -------------  -----  --------  ----------  ------------

 1/1      1     not-connected      4        32   disabled              

 1/2      1     not-connected      4        32   disabled              

 4/1      1     type-pvid-inconsistent    100        32   disabled              

 4/2      1     not-connected    100        32   disabled              


<...output truncated...>



Switch 2> (enable) show spantree statistics 4/1

Port  4/1 VLAN 1


SpanningTree enabled for vlanNo = 1


                BPDU-related parameters

port spanning tree                   enabled

state                                broken

port_id                              0x8142

port number                          0x142

path cost                            100

message age (port/VLAN)              1(20)

designated_root                      00-60-09-79-c3-00

designated_cost                      0

designated_bridge                    00-60-09-79-c3-00

designated_port                      0x8142

top_change_ack                       FALSE

config_pending                       FALSE

port_inconsistency                   port_type & port_vlan


<...output truncated...>

Switch 2> (enable)

Step 3 Resolve the misconfiguration by completing the 802.1Q configuration on Switch 2: 

Switch 2> (enable) set trunk 4/1 nonegotiate dot1q

Port(s) 4/1 trunk mode set to nonegotiate.

Port(s) 4/1 trunk type set to dot1q.

Switch 2> (enable) 2/20/1998,23:41:15:DISL-5:Port 4/1 has become dot1q trunk

Port 4/1 on Switch 2 changes from blocking mode to forwarding mode once the port-type inconsistency is resolved (see ). (This assumes that there is no wiring loop present that would cause the port to be blocked normally by spanning tree. In either case, the port state would change from "type-pvid-inconsistent" to "blocking" in the show spantree output.)

Figure 11-5 IEEE 802.1Q Trunking: Final Network Configuration

Step 4 Verify the 802.1Q configuration on Switch 1 by entering the show trunk and show spantree commands: 

Switch 1> (enable) show trunk 1/1

Port      Mode         Encapsulation  Status        Native vlan

--------  -----------  -------------  ------------  -----------

 1/1      nonegotiate  dot1q          trunking      1


Port      Vlans allowed on trunk

--------  ---------------------------------------------------------------------

 1/1      1-1005


Port      Vlans allowed and active in management domain 

--------  ---------------------------------------------------------------------

 1/1      1-3,1003,1005


Port      Vlans in spanning tree forwarding state and not pruned

--------  ---------------------------------------------------------------------

 1/1      1005

Switch 1> (enable) show spantree 1

VLAN 1

Spanning tree enabled

Spanning tree type          ieee


Designated Root             00-60-09-79-c3-00

Designated Root Priority    32768

Designated Root Cost        0

Designated Root Port        1/1

Root Max Age   20 sec    Hello Time 2  sec   Forward Delay 15 sec


Bridge ID MAC ADDR          00-10-29-b5-30-00

Bridge ID Priority          49152

Bridge Max Age 20 sec    Hello Time 2  sec   Forward Delay 15 sec


Port      Vlan  Port-State     Cost   Priority  Fast-Start  Group-method

--------- ----  -------------  -----  --------  ----------  ------------

 1/1      1     forwarding         4        32   disabled              

 1/2      1     not-connected      4        32   disabled 


<...output truncated...>

Switch 1> (enable)

The output shows that port 1/1 is an IEEE 802.1Q trunk port, that its status is "trunking," and that the port-state is "forwarding."

Step 5 Verify the configuration on Switch 2 by entering the show trunk and show spantree commands: 

Switch 2> (enable) show trunk 4/1

Port      Mode         Encapsulation  Status        Native vlan

--------  -----------  -------------  ------------  -----------

 4/1      nonegotiate  dot1q          trunking      1


Port      Vlans allowed on trunk

--------  ---------------------------------------------------------------------

 4/1      1-1005


Port      Vlans allowed and active in management domain 

--------  ---------------------------------------------------------------------

 4/1      1-3,1003,1005


Port      Vlans in spanning tree forwarding state and not pruned

--------  ---------------------------------------------------------------------

 4/1      1005

Switch 2> (enable) show spantree 1

VLAN 1

Spanning tree enabled

Spanning tree type          ieee


Designated Root             00-60-09-79-c3-00

Designated Root Priority    32768

Designated Root Cost        0

Designated Root Port        1/0

Root Max Age   20 sec    Hello Time 2  sec   Forward Delay 15 sec


Bridge ID MAC ADDR          00-60-09-79-c3-00

Bridge ID Priority          32768

Bridge Max Age 20 sec    Hello Time 2  sec   Forward Delay 15 sec


Port      Vlan  Port-State     Cost   Priority  Fast-Start  Group-method

--------- ----  -------------  -----  --------  ----------  ------------

 1/1      1     not-connected      4        32   disabled              

 1/2      1     not-connected      4        32   disabled              

 4/1      1     forwarding       100        32   disabled              

 4/2      1     not-connected    100        32   disabled 

<...output truncated...>

Switch 2> (enable)

The output shows that port 4/1 is an IEEE 802.1Q trunk port, that its status is "trunking," and that the port-state is "forwarding."

Step 6 Verify connectivity across the trunk using the ping command: 

Switch 1> (enable) ping switch_2

switch_2 is alive

Switch 1> (enable)