This document provides sample configurations for IEEE 802.1Q trunking between Catalyst switches running Catalyst OS (CatOS) system software and modular Layer 3 (L3) switches running Cisco IOS® System Software. Switches running CatOS include the Catalyst 4500/4000, 5500/5000, and 6500/6000 series switches. Modular L3 switches running Cisco IOS Software include the Catalyst 4500/4000 and Catalyst 6500/6000 series switches. The sample configurations use a Catalyst 4000 (CatOS) and a Catalyst 6500 (Cisco IOS Software), but any of the switches just mentioned could have been used to achieve the same results.
Trunking is a way to carry traffic from several VLANs over a point-to-point link between the two devices. Two ways that Ethernet trunking can be implemented are:
Inter-Switch Link Protocol (ISL) (Cisco proprietary protocol)
802.1Q (IEEE standard)
For system requirements, guidelines and restrictions related to 802.1Q and ISL on Catalyst switches, refer to: System Requirements to Implement Trunking.
To create the examples in this document, these switches were used:
Catalyst 4000 switch with Supervisor Engine II (WS-X4013) running CatOS software version 8.1.3
Catalyst 6509 with Supervisor Engine 2/Multilayer Switch Feature Card 2 (MSFC2) running Cisco IOS Software Release 12.1(20)E2 on the Supervisor Engine and MSFC2
The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If your network is live, make sure that you understand the potential impact of any command.
For more information on document conventions, refer to Cisco Technical Tips Conventions.
This document includes only the configuration files from the switches and the output from the related sample show commands. For details on how to configure an 802.1Q trunk between Catalyst switches, refer to the LAN Product Support Pages.
In 802.1Q trunking, all VLAN packets are tagged on the trunk link, except the native VLAN. The native VLAN packets are sent untagged on the trunk link. Therefore, the native VLAN should be the same on both switches configured for trunking. This way, you can deduce to which VLAN a frame belongs when you receive a frame with no tag. By default, VLAN 1 is the native VLAN on all switches.
In CatOS, the native VLAN can be changed by issuing the set vlan vlan-id mod/port command, where mod/port is the trunk port.
In Cisco IOS Software, the native VLAN can be changed by issuing the switchport trunk native vlan vlan-id interface command which is configured on the trunk port.
In this section, you are presented with the information to configure the features described in this document.
The configurations in this document were implemented in an isolated lab environment. Ensure that you understand the potential impact of any configuration or command on your network before using it. The configurations on all devices were cleared with the clear config all and write erase commands to ensure that they had a default configuration.
Note: To find additional information on the commands used in this document, use the Command Lookup Tool (registered customers only) .
This document uses this network setup:
This document uses these configurations:
Note: Comments and explanations are displayed in blue italics.
Catalyst 4000 Switch |
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#version 8.1(3) ! ! #system web interface version(s) ! #system set system name cat4000 ! #frame distribution method set port channel all distribution mac both ! #vtp set vtp domain cisco !--- In this example, the VLAN Trunk Protocol (VTP) domain name is the same !--- on both sides. This is required for the autonegotiation of the trunk !--- by the Dynamic Trunking Protocol (DTP). set vtp mode client vlan !--- In this example, the VTP mode is set to client. !--- Set the VTP mode according to your network requirements. !--- For more details, refer to !--- Understanding and Configuring VLAN Trunk Protocol (VTP). ! #ip set interface sc0 1 10.10.10.2/255.255.255.0 10.10.10.255 !--- This is the IP address used for management. !--- Output suppressed. ! #module 1 : 2-port 1000BaseX Supervisor ! #module 2 empty ! #module 3 empty ! #module 4 empty ! #module 5 : 48-port Inline Power Module set vlan 2 5/13-24 !--- Ports 5/13-24 have been assigned to VLAN 2. set trunk 5/1 desirable dot1q 1-1005,1025-4094 !--- The trunking mode is set to desirable mode, which means !--- the port automatically tries to form a trunk with a !--- neighboring port set to desirable, auto, or on mode. !--- For recommended trunk mode settings, refer to !--- the Dynamic Trunking Protocol section of !--- Best Practices for Catalyst 4500/4000, 5500/5000, and 6500/6000 Series Switches Running CatOS Configuration and Management. !--- Output suppressed. set spantree portfast 5/2-24 enable set port channel 5/2-24 mode off !--- The macro command set port host 5/2-24 was used to do three things: !--- disable trunking, disable port channeling, and enable spantree portfast. !--- For details on using the set port host command, refer to !--- Using Portfast and Other Commands to Fix Workstation Startup Connectivity Delays. ! #module 6 empty end |
Catalyst 6500 Switch |
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Current configuration : 4408 bytes ! version 12.1 service timestamps debug uptime service timestamps log uptime no service password-encryption ! hostname cat6500 ! boot system flash sup-bootflash:c6sup22-jsv-mz.121-20.E2 enable password mysecret !--- This is the privileged mode password used in the example. ! ip subnet-zero ! ! ! mls flow ip destination mls flow ipx destination ! redundancy mode rpr-plus main-cpu auto-sync running-config auto-sync standard ! ! ! interface GigabitEthernet2/1 no ip address shutdown ! interface GigabitEthernet2/2 no ip address shutdown ! interface fastethernet3/1 switchport !--- The switchport command must be entered once, !--- without any keywords, to configure the interface as a Layer 2 port. !--- The interface is now automatically configured with the default command !--- switchport mode dynamic desirable. !--- This means the interface is ready to autonegotiate trunking !--- encapsulation and form a trunk link (using DTP) with a neighbor port !--- in desirable, auto, or on mode. !--- For recommended trunk mode settings, refer to !--- the "Dynamic Trunking Protocol" section of !--- Best Practices for Catalyst 6500/6000 Series and Catalyst 4500/4000 Series Switches Running Cisco IOS Software. ! interface FastEthernet3/2 switchport switchport mode access spanning-tree portfast !--- The interface range fastethernet mod/beginport - endport !--- command is used to configure interfaces 3/2 - 24 at once. !--- Next, the switchport command is issued (if this has not been done already). switchport mode access spanning-tree portfast !--- Next, issue the macro command switchport host 3/2 - 24 to automatically !--- configure these ports as access ports and to enable spantree portfast. !--- For details on using the switchport host command, refer to !--- Using Portfast and Other Commands to Fix Workstation Startup Connectivity Delays. ! interface FastEthernet3/13 switchport switchport access vlan 2 !--- Interfaces 3/13 - 24 are placed in VLAN 2 !--- using the switchport access vlan 2 command. switchport mode access spanning-tree portfast !--- Output suppressed. ! interface FastEthernet3/24 shutdown switchport switchport access vlan 2 switchport mode access spanning-tree portfast !--- Output suppressed. ! interface FastEthernet3/48 no ip address shutdown ! interface vlan 1 ip address 10.10.10.3 255.255.255.0 !--- This is the IP address used for management. ! ip classless no ip http server ! ! ! line con 0 line vty 0 4 password mysecret !--- This is the Telnet password used in the example. login transport input lat pad mop telnet rlogin udptn nasi ! ! end cat6500# |
This section provides information you can use to confirm your configuration is working properly.
Certain show commands are supported by the Output Interpreter (registered customers only) tool, which allows you to view an analysis of show command output.
On Catalyst switches running CatOS, use these commands:
show port capabilities module/port
show port module/port
show trunk module/port
show vtp domain
On Catalyst 6000 switches running Cisco IOS Software, use the following commands:
show interfaces interface-type module/port trunk
show vlan
The show port capabilities module/port command is used to check whether the port is capable of trunking.
cat4000> (enable) show port capabilities 5/1 Model WS-X4148-RJ45V Port 5/1 Type 10/100BaseTX Speed auto,10,100 Duplex half,full Trunk encap type 802.1Q Trunk mode on,off,desirable,auto,nonegotiate Channel 5/1-48 Flow control no Security yes Dot1x yes Membership static,dynamic Fast start yes QOS scheduling rx-(none),tx-(2q1t) CoS rewrite no ToS rewrite no Rewrite no UDLD yes Inline power auto,off,static AuxiliaryVlan 1..1000,1025..4094,untagged,none SPAN source,destination,reflector Link debounce timer yes IGMPFilter yes Dot1q-all-tagged no cat4000> (enable)
The show port module/port command shows the status of a particular port and whether it is trunking.
cat4000> (enable) show port status 5/1 Port Name Status Vlan Level Duplex Speed Type ----- ------------------ ---------- ---------- ------ ------ ----- ------------ 5/1 connected trunk normal a-full a-100 10/100BaseTX cat4000> (enable)
The show trunk command is used to verify the trunking status and configuration.
cat4000> (enable) show trunk * - indicates vtp domain mismatch # - indicates dot1q-all-tagged enabled on the port Port Mode Encapsulation Status Native vlan -------- ----------- ------------- ------------ ----------- 5/1 desirable dot1q trunking 1 Port Vlans allowed on trunk -------- --------------------------------------------------------------------- 5/1 1-1005,1025-4094 Port Vlans allowed and active in management domain -------- --------------------------------------------------------------------- 5/1 1-2 Port Vlans in spanning tree forwarding state and not pruned -------- --------------------------------------------------------------------- 5/1 1-2 cat4000> (enable)
The show vtp domain command is used to check the VTP information.
cat4000> (enable) show vtp domain Version : running VTP1 (VTP3 capable) Domain Name : cisco Password : not configured Notifications: disabled Updater ID: 10.10.10.3 Feature Mode Revision -------------- -------------- ----------- VLAN Client 21 Pruning : disabled VLANs prune eligible: 2-1000
The show interfaces interface-type module/port trunk command tells whether the port is trunking.
cat6500# show interfaces fastethernet 3/1 trunk Port Mode Encapsulation Status Native vlan Fa3/1 desirable n-802.1q trunking 1 Port Vlans allowed on trunk Fa3/1 1-4094 Port Vlans allowed and active in management domain Fa3/1 1-2 Port Vlans in spanning tree forwarding state and not pruned Fa3/1 1-2 cat6500#
The show vlan command gives information about the VLANs and the ports that belong to a particular VLAN.
cat6500# show vlan VLAN Name Status Ports ---- -------------------------------- --------- ------------------------------- 1 default active Fa3/2, Fa3/3, Fa3/4, Fa3/5 Fa3/6, Fa3/7, Fa3/8, Fa3/9 Fa3/10, Fa3/11, Fa3/12 2 VLAN0002 active Fa3/13, Fa3/14, Fa3/15, Fa3/16 Fa3/17, Fa3/18, Fa3/19, Fa3/20 Fa3/21, Fa3/22, Fa3/23, Fa3/24 1002 fddi-default act/unsup 1003 token-ring-default act/unsup 1004 fddinet-default act/unsup 1005 trnet-default act/unsup !--- Output suppressed. cat6500#
Note: Only those ports that are configured as Layer 2 nontrunk ports are displayed.
There is currently no specific troubleshooting information available for this configuration.