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This chapter describes how to configure Fast Ethernet and Gigabit Ethernet virtual LAN (VLAN) trunks.
This chapter consists of these sections:
These sections describe how VLAN trunks work on the Catalyst 5000, 4000, 2948G, and 2926G series switches:
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:
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 "Configuring Fast EtherChannel and Gigabit EtherChannel."
Fast Ethernet and Gigabit Ethernet trunk ports support five different trunking modes (see Table 11-1). 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.
For trunking to be autonegotiated on Fast Ethernet and Gigabit Ethernet ports, the ports must be in the same VTP domain. However, you can use the on or nonegotiate mode to force a port to become a trunk, even if it is in a different domain. For more information on VTP domains, see "Configuring VTP."
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.
Table 11-1 lists the trunking modes used with the set trunk command and describes how they function on Fast Ethernet and Gigabit Ethernet ports.
| 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 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.
| 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. Table 11-3 shows the result of the possible trunking 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 | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: |
on | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: |
desirable | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: |
auto | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: |
on | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: |
desirable | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: |
auto | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: |
desirable negotiate | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: |
auto | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: | Local: Neighbor: |
| 1Using this configuration can result in spanning-tree loops and is not recommended. |
Trunking capabilities are hardware-dependent. Table 11-4 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.
| Trunking Method | Catalyst 5000 Series | Catalyst 4000 Series | Catalyst 2948G Series | Catalyst 2926G Series |
|---|---|---|---|---|
ISL | Yes | No | No | Yes |
IEEE 802.1Q | Yes | Yes | Yes | Yes |
IEEE 802.1Q trunks impose some limitations on the trunking strategy for a network. The following restrictions apply when using 802.1Q trunks:
Table 11-5 shows the default Fast Ethernet and Gigabit Ethernet trunk configuration.
| Feature | Default Configuration |
|---|---|
Trunk mode | auto |
Trunk encapsulation |
|
Allowed VLAN range | VLANs 1-1005 |
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:
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)
 | 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
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) 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)
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.
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)
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] |
This section contains example VLAN trunk configurations.
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)
This example configuration shows how to configure an ISL trunk over a Fast EtherChannel link between two switches.
Figure 11-1 shows two switches connected through two 100BaseTX Fast Ethernet ports.
This example shows how to configure the switches to form a two-port Fast EtherChannel bundle, and then configure the EtherChannel bundle as an ISL trunk link.
Step 1 You can confirm the channeling and trunking status of the switches using the show port channel and show trunk commands.
Switch_A> (enable) show port channel No ports channelling Switch_A> (enable) show trunk No ports trunking. Switch_A> (enable) Switch_B> (enable) show port channel No ports channelling Switch_B> (enable) show trunk No ports trunking. Switch_B> (enable)
Step 2 Configure the ports on Switch A to negotiate a Fast EtherChannel bundle with the neighboring switch. This example assumes that the neighboring ports on Switch B are in EtherChannel auto mode. The system logging messages provide information about the formation of the EtherChannel bundle.
Switch_A> (enable) set port channel 1/1-2 desirable Port(s) 1/1-2 channel mode set to desirable. Switch_A> (enable) %PAGP-5-PORTFROMSTP:Port 1/1 left bridge port 1/1 %PAGP-5-PORTFROMSTP:Port 1/2 left bridge port 1/2 %PAGP-5-PORTFROMSTP:Port 1/2 left bridge port 1/2 %PAGP-5-PORTTOSTP:Port 1/1 joined bridge port 1/1-2 %PAGP-5-PORTTOSTP:Port 1/2 joined bridge port 1/1-2 Switch_B> (enable) %PAGP-5-PORTFROMSTP:Port 3/1 left bridge port 3/1 %PAGP-5-PORTFROMSTP:Port 3/2 left bridge port 3/2 %PAGP-5-PORTFROMSTP:Port 3/2 left bridge port 3/2 %PAGP-5-PORTTOSTP:Port 3/1 joined bridge port 3/1-2 %PAGP-5-PORTTOSTP:Port 3/2 joined bridge port 3/1-2
Step 3 After the EtherChannel bundle is negotiated, use the show port channel command to verify the configuration.
Switch_A> (enable) show port channel
Port Status Channel Channel Neighbor Neighbor
mode status device port
----- ---------- --------- ----------- ------------------------- ----------
1/1 connected desirable channel WS-C5000 009979082(Sw 3/1
1/2 connected desirable channel WS-C5000 009979082(Sw 3/2
----- ---------- --------- ----------- ------------------------- ----------
Switch_A> (enable)
Switch_B> (enable) show port channel
Port Status Channel Channel Neighbor Neighbor
mode status device port
----- ---------- --------- ----------- ------------------------- ----------
3/1 connected auto channel WS-C5500 069003103(Sw 1/1
3/2 connected auto channel WS-C5500 069003103(Sw 1/2
----- ---------- --------- ----------- ------------------------- ----------
Switch_B> (enable)
Step 4 Configure one of the ports in the EtherChannel bundle to negotiate an ISL trunk. The configuration is applied to all of the ports in the bundle. This example assumes that the neighboring ports on Switch B are configured to use isl or negotiate encapsulation and are in auto trunk mode. The system logging messages provide information about the formation of the ISL trunk.
Switch_A> (enable) set trunk 1/1 desirable isl Port(s) 1/1-2 trunk mode set to desirable. Port(s) 1/1-2 trunk type set to isl. Switch_A> (enable) %DTP-5-TRUNKPORTON:Port 1/1 has become isl trunk %DTP-5-TRUNKPORTON:Port 1/2 has become isl trunk %PAGP-5-PORTFROMSTP:Port 1/1 left bridge port 1/1-2 %PAGP-5-PORTFROMSTP:Port 1/2 left bridge port 1/1-2 %PAGP-5-PORTTOSTP:Port 1/1 joined bridge port 1/1-2 %PAGP-5-PORTTOSTP:Port 1/2 joined bridge port 1/1-2 Switch_B> (enable) %DTP-5-TRUNKPORTON:Port 3/1 has become isl trunk %DTP-5-TRUNKPORTON:Port 3/2 has become isl trunk %PAGP-5-PORTFROMSTP:Port 3/1 left bridge port 3/1-2 %PAGP-5-PORTFROMSTP:Port 3/2 left bridge port 3/1-2 %PAGP-5-PORTTOSTP:Port 3/1 joined bridge port 3/1-2 %PAGP-5-PORTTOSTP:Port 3/2 joined bridge port 3/1-2
Step 5 After the ISL trunk link is negotiated, use the show trunk command to verify the configuration.
Switch_A> (enable) show trunk
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 1-5,10,20,50,152,200,300,400,500,521-524,570,850,917,999
1/2 1-5,10,20,50,152,200,300,400,500,521-524,570,850,917,999
Port Vlans in spanning tree forwarding state and not pruned
-------- ---------------------------------------------------------------------
1/1 1-5,10,20,50,152,200,300,400,500,521-524,570,850,917,999
1/2 1-5,10,20,50,152,200,300,400,500,521-524,570,850,917,999
Switch_A> (enable)
Switch_B> (enable) show trunk
Port Mode Encapsulation Status Native vlan
-------- ----------- ------------- ------------ -----------
3/1 auto isl trunking 1
3/2 auto isl trunking 1
Port Vlans allowed on trunk
-------- ---------------------------------------------------------------------
3/1 1-1005
3/2 1-1005
Port Vlans allowed and active in management domain
-------- ---------------------------------------------------------------------
3/1 1-5,10,20,50,152,200,300,400,500,521-524,570,850,917,999
3/2 1-5,10,20,50,152,200,300,400,500,521-524,570,850,917,999
Port Vlans in spanning tree forwarding state and not pruned
-------- ---------------------------------------------------------------------
3/1 1-5,10,20,50,152,200,300,400,500,521-524,570,801,850,917,999
3/2 1-5,10,20,50,152,200,300,400,500,521-524,570,801,850,917,999
Switch_B> (enable)
This example configuration shows how to configure an IEEE 802.1Q trunk over a Gigabit EtherChannel link between two switches with 802.1Q-capable hardware. (Use the show port capabilities command to see if your hardware is 802.1Q-capable.)
Figure 11-2 shows two switches connected through four 1000BaseSX Gigabit Ethernet ports.
This example shows how to configure the switches to form a four-port Gigabit EtherChannel bundle, and then configure the EtherChannel bundle as an IEEE 802.1Q trunk link.
Step 1 Make sure all ports on both Switch A and Switch B are assigned to the same VLAN. This VLAN is used as the IEEE 802.1Q native VLAN for the trunk. In this example, all ports are configured as members of VLAN 1.
Switch_A> (enable) set vlan 1 2/3-6
VLAN Mod/Ports
---- -----------------------
1 2/1-6
Switch_A> (enable)
Switch_B> (enable) set vlan 1 3/3-6
VLAN Mod/Ports
---- -----------------------
1 3/1-6
Switch_B> (enable)
Step 2 You can confirm the channeling and trunking status of the switches using the show port channel and show trunk commands.
Switch_A> (enable) show port channel No ports channelling Switch_A> (enable) show trunk No ports trunking. Switch_A> (enable) Switch_B> (enable) show port channel No ports channelling Switch_B> (enable) show trunk No ports trunking. Switch_B> (enable)
Step 3 Configure the ports on Switch A to negotiate a Gigabit EtherChannel bundle with the neighboring switch. This example assumes that the neighboring ports on Switch B are in EtherChannel auto mode. The system logging messages provide information about the formation of the EtherChannel bundle.
Switch_A> (enable) set port channel 2/3-6 desirable Port(s) 2/3-6 channel mode set to desirable. Switch_A> (enable) %PAGP-5-PORTFROMSTP:Port 2/3 left bridge port 2/3 %PAGP-5-PORTFROMSTP:Port 2/4 left bridge port 2/4 %PAGP-5-PORTFROMSTP:Port 2/5 left bridge port 2/5 %PAGP-5-PORTFROMSTP:Port 2/6 left bridge port 2/6 %PAGP-5-PORTFROMSTP:Port 2/4 left bridge port 2/4 %PAGP-5-PORTFROMSTP:Port 2/5 left bridge port 2/5 %PAGP-5-PORTFROMSTP:Port 2/6 left bridge port 2/6 %PAGP-5-PORTFROMSTP:Port 2/3 left bridge port 2/3 %PAGP-5-PORTTOSTP:Port 2/3 joined bridge port 2/3-6 %PAGP-5-PORTTOSTP:Port 2/4 joined bridge port 2/3-6 %PAGP-5-PORTTOSTP:Port 2/5 joined bridge port 2/3-6 %PAGP-5-PORTTOSTP:Port 2/6 joined bridge port 2/3-6 Switch_B> (enable) %PAGP-5-PORTFROMSTP:Port 3/3 left bridge port 3/3 %PAGP-5-PORTFROMSTP:Port 3/4 left bridge port 3/4 %PAGP-5-PORTFROMSTP:Port 3/5 left bridge port 3/5 %PAGP-5-PORTFROMSTP:Port 3/6 left bridge port 3/6 %PAGP-5-PORTFROMSTP:Port 3/4 left bridge port 3/4 %PAGP-5-PORTFROMSTP:Port 3/5 left bridge port 3/5 %PAGP-5-PORTFROMSTP:Port 3/6 left bridge port 3/6 %PAGP-5-PORTFROMSTP:Port 3/3 left bridge port 3/3 %PAGP-5-PORTTOSTP:Port 3/3 joined bridge port 3/3-6 %PAGP-5-PORTTOSTP:Port 3/4 joined bridge port 3/3-6 %PAGP-5-PORTTOSTP:Port 3/5 joined bridge port 3/3-6 %PAGP-5-PORTTOSTP:Port 3/6 joined bridge port 3/3-6
Step 4 After the EtherChannel bundle is negotiated, use the show port channel command to verify the configuration.
Switch_A> (enable) show port channel
Port Status Channel Channel Neighbor Neighbor
mode status device port
----- ---------- --------- ----------- ------------------------- ----------
2/3 connected desirable channel WS-C4003 JAB023806(Sw 2/3
2/4 connected desirable channel WS-C4003 JAB023806(Sw 2/4
2/5 connected desirable channel WS-C4003 JAB023806(Sw 2/5
2/6 connected desirable channel WS-C4003 JAB023806(Sw 2/6
----- ---------- --------- ----------- ------------------------- ----------
Switch_A> (enable)
Switch_B> (enable) show port channel
Port Status Channel Channel Neighbor Neighbor
mode status device port
----- ---------- --------- ----------- ------------------------- ----------
3/3 connected auto channel WS-C4003 JAB023806(Sw 2/3
3/4 connected auto channel WS-C4003 JAB023806(Sw 2/4
3/5 connected auto channel WS-C4003 JAB023806(Sw 2/5
3/6 connected auto channel WS-C4003 JAB023806(Sw 2/6
----- ---------- --------- ----------- ------------------------- ----------
Switch_B> (enable)
Step 5 Configure one of the ports in the EtherChannel bundle to negotiate an IEEE 802.1Q trunk. The configuration is applied to all of the ports in the bundle. This example assumes that the neighboring ports on Switch B are configured to use dot1q or negotiate encapsulation and are in auto trunk mode. The system logging messages provide information about the formation of the 802.1Q trunk.
Switch_A> (enable) set trunk 2/3 desirable dot1q Port(s) 2/3-6 trunk mode set to desirable. Port(s) 2/3-6 trunk type set to dot1q. Switch_A> (enable) %DTP-5-TRUNKPORTON:Port 2/3 has become dot1q trunk %DTP-5-TRUNKPORTON:Port 2/4 has become dot1q trunk %PAGP-5-PORTFROMSTP:Port 2/3 left bridge port 2/3-6 %DTP-5-TRUNKPORTON:Port 2/5 has become dot1q trunk %PAGP-5-PORTFROMSTP:Port 2/4 left bridge port 2/3-6 %PAGP-5-PORTFROMSTP:Port 2/5 left bridge port 2/3-6 %DTP-5-TRUNKPORTON:Port 2/6 has become dot1q trunk %PAGP-5-PORTFROMSTP:Port 2/6 left bridge port 2/3-6 %PAGP-5-PORTFROMSTP:Port 2/3 left bridge port 2/3 %PAGP-5-PORTTOSTP:Port 2/3 joined bridge port 2/3-6 %PAGP-5-PORTTOSTP:Port 2/4 joined bridge port 2/3-6 %PAGP-5-PORTTOSTP:Port 2/5 joined bridge port 2/3-6 %PAGP-5-PORTTOSTP:Port 2/6 joined bridge port 2/3-6 Switch_B> (enable) %DTP-5-TRUNKPORTON:Port 3/3 has become dot1q trunk %DTP-5-TRUNKPORTON:Port 3/4 has become dot1q trunk %PAGP-5-PORTFROMSTP:Port 3/3 left bridge port 3/3-6 %PAGP-5-PORTFROMSTP:Port 3/4 left bridge port 3/3-6 %PAGP-5-PORTFROMSTP:Port 3/5 left bridge port 3/3-6 %PAGP-5-PORTFROMSTP:Port 3/6 left bridge port 3/3-6 %DTP-5-TRUNKPORTON:Port 3/5 has become dot1q trunk %DTP-5-TRUNKPORTON:Port 3/6 has become dot1q trunk %PAGP-5-PORTFROMSTP:Port 3/5 left bridge port 3/3-6 %PAGP-5-PORTFROMSTP:Port 3/6 left bridge port 3/3-6 %PAGP-5-PORTTOSTP:Port 3/3 joined bridge port 3/3-6 %PAGP-5-PORTTOSTP:Port 3/4 joined bridge port 3/3-6 %PAGP-5-PORTTOSTP:Port 3/5 joined bridge port 3/3-6 %PAGP-5-PORTTOSTP:Port 3/6 joined bridge port 3/3-6
Step 6 After the 802.1Q trunk link is negotiated, use the show trunk command to verify the configuration.
Switch_A> (enable) show trunk Port Mode Encapsulation Status Native vlan -------- ----------- ------------- ------------ ----------- 2/3 desirable dot1q trunking 1 2/4 desirable dot1q trunking 1 2/5 desirable dot1q trunking 1 2/6 desirable dot1q trunking 1 Port Vlans allowed on trunk -------- --------------------------------------------------------------------- 2/3 1-1005 2/4 1-1005 2/5 1-1005 2/6 1-1005 Port Vlans allowed and active in management domain -------- --------------------------------------------------------------------- 2/3 1-5,10,20,50,152,200,300,400,500,521-524,570,850,917,999 2/4 1-5,10,20,50,152,200,300,400,500,521-524,570,850,917,999 2/5 1-5,10,20,50,152,200,300,400,500,521-524,570,850,917,999 2/6 1-5,10,20,50,152,200,300,400,500,521-524,570,850,917,999 Port Vlans in spanning tree forwarding state and not pruned -------- --------------------------------------------------------------------- 2/3 2/4 2/5 2/6 Switch_A> (enable) Switch_B> (enable) show trunk Port Mode Encapsulation Status Native vlan -------- ----------- ------------- ------------ ----------- 3/3 auto dot1q trunking 1 3/4 auto dot1q trunking 1 3/5 auto dot1q trunking 1 3/6 auto dot1q trunking 1 Port Vlans allowed on trunk -------- --------------------------------------------------------------------- 3/3 1-1005 3/4 1-1005 3/5 1-1005 3/6 1-1005 Port Vlans allowed and active in management domain -------- --------------------------------------------------------------------- 3/3 1-5,10,20,50,152,200,300,400,500,521-524,570,850,917,999 3/4 1-5,10,20,50,152,200,300,400,500,521-524,570,850,917,999 3/5 1-5,10,20,50,152,200,300,400,500,521-524,570,850,917,999 3/6 1-5,10,20,50,152,200,300,400,500,521-524,570,850,917,999 Port Vlans in spanning tree forwarding state and not pruned -------- --------------------------------------------------------------------- 3/3 1-5,10,20,50,152,200,300,400,500,521-524,570,850,917,999 3/4 1-5,10,20,50,152,200,300,400,500,521-524,570,850,917,999 3/5 1-5,10,20,50,152,200,300,400,500,521-524,570,850,917,999 3/6 1-5,10,20,50,152,200,300,400,500,521-524,570,850,917,999 Switch_B> (enable)
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 11-3 shows a parallel trunk configuration between two switches, using the Fast Ethernet uplink ports on the supervisor engine.
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 11-4 shows the network after you configure VLAN traffic load-sharing.
Figure 11-4 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 11-4, 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)
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 to see if your hardware is 802.1Q-capable.)
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 Figure 11-5. Assume that the native VLAN is VLAN 1 on both ends of the link.
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 Figure 11-6). Port 4/1 would also be blocked if it were configured as a nontrunk port.
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 Figure 11-7). (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.)
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)
Posted: Mon Jul 19 12:39:08 PDT 1999
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