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This chapter describes how to configure:
This chapter consists of these sections:
A trunk is a point-to-point link between two Catalyst switch ports or between a Catalyst switch and a router. Trunks carry the traffic of multiple VLANs and allow you to extend VLANs across an entire network.
VLAN trunks can use Cisco's ISL or industry-standard IEEE 802.1Q encapsulation to carry traffic for multiple VLANs over a single link. Trunk ports support five different trunking modes (see Table 6-1). In addition, 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). DTP supports autonegotiation of both ISL and IEEE 802.1Q trunks.
Table 6-1 lists the trunking modes used with the set trunk command and describes how they function on Ethernet ports. Table 6-2 lists the encapsulation types used with the set trunk command and describes how they function on 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. |
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. |
| Encapsulation | Function |
|---|---|
isl | Specifies ISL encapsulation on the trunk link. If no trunk encapsulation type is specified when configuring an Ethernet trunk, ISL is used as the default. |
dot1q | Specifies IEEE 802.1Q encapsulation. |
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. |
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 6-3 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. |
Table 6-4 shows the default Ethernet trunk configuration.
| Feature | Default Configuration |
|---|---|
Trunk enable state | disable |
Trunk mode | auto |
Trunk encapsulation | isl |
Allowed VLAN range | 1-1005 |
These sections describe how to configure a trunk on Ethernet ports and how to define the allowed VLAN range on a trunk:
To configure a port as an ISL trunk (the default for Ethernet ports), perform this task in privileged mode:
| Task | Command |
|---|---|
Step 1 Configure a port as an ISL trunk. | set trunk mod_num/port_num [on | desirable | auto | nonegotiate] |
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)
To configure a port as an IEEE 802.1Q trunk, perform this task in privileged mode:
| Task | Command |
|---|---|
Step 1 Configure a port as 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:
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)
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)
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 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 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 supervisor engine Ethernet uplink port) on Switch 1 is connected to an Ethernet port on another Catalyst 6000 or 6500 series 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 To configure port 1/1 on Switch 1 as an ISL trunk port, enter the set trunk command. By specifying the desirable keyword, the trunk is automatically negotiated with the neighboring port (port 1/2 on Switch 2).
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, enter the clear trunk command to remove the VLANs that should not pass traffic over the trunk link. The arrow indicates the line that shows the allowed VLANs list.
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)
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 (rather than keeping one trunk in blocking mode), which reduces the total traffic carried over each trunk while still maintaining a fault-tolerant configuration.
Figure 6-1 shows a parallel trunk configuration between two switches, using the Ethernet uplink ports on the supervisor engine.
By default, the port-VLAN priority for both trunks is equal (a value of 32). Therefore, spanning-tree protocol 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 two 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:DTP-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:DTP-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 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 Spanning tree takes one to two minutes to converge. After 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 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 6-2 shows the network after you configure VLAN traffic load-sharing.
Figure 6-2 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 6-2, STP reconverges to use Trunk 2 to forward traffic from all the VLANs, as shown in this example:
Switch_1> (enable) 04/21/1998,03:15:40:DTP-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)
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