You are on page 1of 9


1Q Trunking Between Catalyst Switches Running CatOS and Cisco IOS System Software
Document ID: 8760

Introduction Prerequisites Requirements Components Used Conventions Background Theory Configure Network Diagram Configurations Verify show Commands Sample show Command Output Troubleshoot Related Information

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.

Components Used
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

Note: To find additional information on the commands used in this document. Therefore. • In Cisco IOS Software. make sure that you understand the potential impact of any command. • In CatOS. VLAN 1 is the native VLAN on all switches. In 802. all VLAN packets are tagged on the trunk link. Background Theory This document includes only the configuration files from the switches and the output from the related sample show commands. except the native VLAN.1Q trunking. If your network is live. you are presented with the information to configure the features described in this document. For details on how to configure an 802. The configurations in this document were implemented in an isolated lab environment.1(20)E2 on the Supervisor Engine and MSFC2 The information in this document was created from the devices in a specific lab environment. refer to Cisco Technical Tips Conventions. The native VLAN packets are sent untagged on the trunk link.• Catalyst 6509 with Supervisor Engine 2/Multilayer Switch Feature Card 2 (MSFC2) running Cisco IOS Software Release 12.1Q trunk between Catalyst switches. By default. This way. the native VLAN can be changed by issuing the switchport trunk native vlan vlan−id interface command which is configured on the trunk port. use the Command Lookup Tool (registered customers only) . Network Diagram This document uses this network setup: . refer to the LAN Product Support Pages. the native VLAN can be changed by issuing the set vlan vlan−id mod/port command. the native VLAN should be the same on both switches configured for trunking. Ensure that you understand the potential impact of any configuration or command on your network before using it. you can deduce to which VLAN a frame belongs when you receive a frame with no tag. Configure In this section. All of the devices used in this document started with a cleared (default) configuration. Conventions For more information on document conventions. where mod/port is the trunk port. The configurations on all devices were cleared with the clear config all and write erase commands to ensure that they had a default configuration.

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. Catalyst 4000 Switch #version 8. the VLAN Trunk Protocol (VTP) domain name is the same !−−− on both sides. the VTP mode is set to client. .Configurations This document uses these configurations: • Catalyst 4000 Switch • Catalyst 6500 Switch Note: Comments and explanations are displayed in blue italics. set vtp mode client vlan !−−− In this example. !−−− Set the VTP mode according to your network requirements. This is required for the autonegotiation of the trunk !−−− by the Dynamic Trunking Protocol (DTP).

0 10. ! #module 6 empty end Catalyst 6500 Switch Current configuration : 4408 bytes ! version 12. set trunk 5/1 desirable dot1q 1−1005. which means !−−− the port automatically tries to form a trunk with a !−−− neighboring port set to desirable.!−−− For more details. 5500/5000.10. !−−− Output suppressed. refer to !−−− Understanding and Configuring VLAN Trunk Protocol (VTP). ! #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. refer to !−−− the Dynamic Trunking Protocol section of !−−− Best Practices for Catalyst 4500/4000. !−−− For details on using the set port host command. !−−− For recommended trunk mode settings. and enable spantree portfast. 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. ! #ip set interface sc0 1 10.2/ !−−− This is the IP address used for management.10. auto.1 service timestamps debug uptime service timestamps log uptime no service password−encryption ! . !−−− Output suppressed.1025−4094 !−−− The trunking mode is set to desirable mode. or on mode.10.10. refer to !−−− Using Portfast and Other Commands to Fix Workstation Startup Connectivity Delays. and 6500/6000 Series Switches Running CatOS Configuration and Management. disable port channeling.

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. The interface is now automatically configured with the default command switchport mode dynamic desirable. the switchport command is issued (if this has not been done already). without any keywords. !−−− This means the interface is ready to autonegotiate trunking !−−− encapsulation and form a trunk link (using DTP) with a neighbor port !−−− in desirable.hostname cat6500 ! boot system flash sup−bootflash:c6sup22−jsv−mz. or on mode. !−−− Next. !−−− For recommended trunk mode settings. ! 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. to configure the interface as a Layer 2 port. switchport mode access spanning−tree portfast . ! 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.E2 enable password mysecret !−−− This is the privileged mode password used in the example. auto.121−20.

10. ! interface FastEthernet3/48 no ip address shutdown ! interface vlan 1 ip address 10.255. issue the macro command switchport host 3/2 − 24 to automatically !−−− configure these ports as access ports and to enable spantree portfast.10. login transport input lat pad mop telnet rlogin udptn nasi ! ! end cat6500# .!−−− Next. !−−− For details on using the switchport host command.255.0 !−−− This is the IP address used for management. switchport mode access spanning−tree portfast !−−− Output suppressed.3 255. ! interface FastEthernet3/24 shutdown switchport switchport access vlan 2 switchport mode access spanning−tree portfast !−−− Output suppressed. ! interface FastEthernet3/13 switchport switchport access vlan 2 !−−− Interfaces 3/13 − 24 are placed in VLAN 2 !−−− using the switchport access vlan 2 command. refer to !−−− Using Portfast and Other Commands to Fix Workstation Startup Connectivity Delays. ! ip classless no ip http server ! ! ! line con 0 line vty 0 4 password mysecret !−−− This is the Telnet password used in the example.

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 This section provides information you can use to confirm your configuration is working properly.1000.100 Duplex half.tx−(2q1t) CoS rewrite no ToS rewrite no Rewrite no UDLD yes Inline power auto. 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. cat4000> (enable) show port capabilities 5/1 Model WS−X4148−RJ45V Port 5/1 Type 10/100BaseTX Speed auto. On Catalyst switches running CatOS. which Sample show Command Output Catalyst 4000 Switch The show port capabilities module/port command is used to check whether the port is capable of trunking. cat4000> (enable) show port status 5/1 Port Name Status Vlan Level Duplex Speed Type .off.static AuxiliaryVlan 1.dynamic Fast start yes QOS scheduling rx−(none).4094. use the following commands: • show interfaces interface−type module/port trunk • show vlan (registered customers only) tool..none SPAN source.untagged.10.1Q Trunk mode show Commands Certain show commands are supported by the Output Interpreter allows you to view an analysis of show command output.nonegotiate Channel 5/1−48 Flow control no Security yes Dot1x yes Membership static.full Trunk encap type 802.1025.

10.1025−4094 Vlans allowed and active in management domain −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− 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.1q Status trunking Native vlan 1 Vlans allowed on trunk 1−4094 Vlans allowed and active in management domain 1−2 Vlans in spanning tree forwarding state and not pruned 1−2 The show vlan command gives information about the VLANs and the ports that belong to a particular VLAN. cat4000> (enable) show trunk * − indicates vtp domain mismatch # − indicates dot1q−all−tagged enabled on the port Port Mode Encapsulation Status −−−−−−−− −−−−−−−−−−− −−−−−−−−−−−−− −−−−−−−−−−−− 5/1 desirable dot1q trunking Port −−−−−−−− 5/1 Port −−−−−−−− 5/1 Native vlan −−−−−−−−−−− 1 Vlans allowed on trunk −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− 1−1005. cat6500# show interfaces fastethernet 3/1 trunk Port Fa3/1 Port Fa3/1 Port Fa3/1 Port Fa3/1 cat6500# Mode desirable Encapsulation n−802.−−−−− −−−−−−−−−−−−−−−−−− −−−−−−−−−− −−−−−−−−−− −−−−−− −−−−−− −−−−− −−−−−−−−−−−− 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.10. cat6500# show vlan . cat4000> (enable) show vtp domain Version : running VTP1 (VTP3 capable) Domain Name : cisco Notifications: disabled Feature Mode Revision −−−−−−−−−−−−−− −−−−−−−−−−−−−− −−−−−−−−−−− VLAN Client 21 Pruning : disabled VLANs prune eligible: 2−1000 Password : not configured Updater ID: 10.3 Catalyst 6500 Switch The show interfaces interface−type module/port trunk command tells whether the port is trunking.

VLAN Name Status Ports −−−− −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− −−−−−−−−− −−−−−−−−−−−−−−−−−−−−−−−−−−−−−−− 1 default active Fa3/2. Inc. Fa3/16 Fa3/17. All rights reserved. Updated: Nov 17. Related Information • LAN Product Support Pages • LAN Switching Support Page • Technical Support − Cisco Systems Contacts & Feedback | Help | Site Map © 2011 − 2012 Cisco Systems. Fa3/11. Fa3/14. 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. Fa3/5 Fa3/6. Troubleshoot There is currently no specific troubleshooting information available for this configuration. Fa3/22. Fa3/4. Fa3/8. Fa3/3. cat6500# Note: Only those ports that are configured as Layer 2 nontrunk ports are displayed. Fa3/20 Fa3/21. Fa3/9 Fa3/10. Fa3/12 2 VLAN0002 active Fa3/13. Fa3/18. Fa3/19. Fa3/7. Fa3/23. Terms & Conditions | Privacy Statement | Cookie Policy | Trademarks of Cisco Systems. Fa3/15. Inc. 2007 Document ID: 8760 .