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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

make sure that you understand the potential impact of any command. In 802. Therefore. the native VLAN can be changed by issuing the set vlan vlan−id mod/port command. All of the devices used in this document started with a cleared (default) configuration. The configurations on all devices were cleared with the clear config all and write erase commands to ensure that they had a default configuration. except the native VLAN. If your network is live. Conventions For more information on document conventions. The native VLAN packets are sent untagged on the trunk link. where mod/port is the trunk port.1Q trunking. • In CatOS. the native VLAN can be changed by issuing the switchport trunk native vlan vlan−id interface command which is configured on the trunk port. VLAN 1 is the native VLAN on all switches. use the Command Lookup Tool (registered customers only) . you can deduce to which VLAN a frame belongs when you receive a frame with no tag. • In Cisco IOS Software. Network Diagram This document uses this network setup: . Background Theory This document includes only the configuration files from the switches and the output from the related sample show commands.1(20)E2 on the Supervisor Engine and MSFC2 The information in this document was created from the devices in a specific lab environment. By default. the native VLAN should be the same on both switches configured for trunking. Note: To find additional information on the commands used in this document.• Catalyst 6509 with Supervisor Engine 2/Multilayer Switch Feature Card 2 (MSFC2) running Cisco IOS Software Release 12. Configure In this section.1Q trunk between Catalyst switches. refer to the LAN Product Support Pages. This way. For details on how to configure an 802. refer to Cisco Technical Tips Conventions. all VLAN packets are tagged on the trunk link. 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.

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

1 service timestamps debug uptime service timestamps log uptime no service password−encryption ! . 5500/5000. !−−− For recommended trunk mode settings. ! #module 6 empty end Catalyst 6500 Switch Current configuration : 4408 bytes ! version 12. ! #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 2.10. or on mode.255.255 !−−− This is the IP address used for management.10. !−−− For details on using the set port host command.1025−4094 !−−− The trunking mode is set to desirable mode. refer to !−−− Understanding and Configuring VLAN Trunk Protocol (VTP). set trunk 5/1 desirable dot1q 1−1005. !−−− Output suppressed. ! #ip set interface sc0 1 10.2/255. and 6500/6000 Series Switches Running CatOS Configuration and Management. !−−− Output suppressed. which means !−−− the port automatically tries to form a trunk with a !−−− neighboring port set to desirable.10. 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.0 10.10. and enable spantree portfast. refer to !−−− Using Portfast and Other Commands to Fix Workstation Startup Connectivity Delays. disable port channeling.255. auto. refer to !−−− the Dynamic Trunking Protocol section of !−−− Best Practices for Catalyst 4500/4000.!−−− For more details.

! 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. 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. or on mode. the switchport command is issued (if this has not been done already). The interface is now automatically configured with the default command switchport mode dynamic desirable. switchport mode access spanning−tree portfast . !−−− Next. ! 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.hostname cat6500 ! boot system flash sup−bootflash:c6sup22−jsv−mz. auto. to configure the interface as a Layer 2 port. !−−− This means the interface is ready to autonegotiate trunking !−−− encapsulation and form a trunk link (using DTP) with a neighbor port !−−− in desirable.121−20.E2 enable password mysecret !−−− This is the privileged mode password used in the example. !−−− For recommended trunk mode settings.

255. switchport mode access spanning−tree portfast !−−− Output suppressed. login transport input lat pad mop telnet rlogin udptn nasi ! ! end cat6500# . ! interface FastEthernet3/48 no ip address shutdown ! interface vlan 1 ip address 10. ! ip classless no ip http server ! ! ! line con 0 line vty 0 4 password mysecret !−−− This is the Telnet password used in the example.255. !−−− For details on using the switchport host command.0 !−−− This is the IP address used for management.10.3 255. ! 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. issue the macro command switchport host 3/2 − 24 to automatically !−−− configure these ports as access ports and to enable spantree portfast.10.!−−− Next.

cat4000> (enable) show port capabilities 5/1 Model WS−X4148−RJ45V Port 5/1 Type 10/100BaseTX Speed auto. cat4000> (enable) show port status 5/1 Port Name Status Vlan Level Duplex Speed Type .untagged.none SPAN source.. 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.desirable.1025.tx−(2q1t) CoS rewrite no ToS rewrite no Rewrite no UDLD yes Inline power auto. show Commands Certain show commands are supported by the Output Interpreter allows you to view an analysis of show command output.1Q Trunk mode on.100 Duplex Fast start yes QOS scheduling rx−(none).Verify This section provides information you can use to confirm your configuration is working properly..4094.nonegotiate Channel 5/1−48 Flow control no Security yes Dot1x yes Membership static.full Trunk encap type 802. use the following commands: • show interfaces interface−type module/port trunk • show vlan (registered customers only) tool. 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.1000.destination.static AuxiliaryVlan 1.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. On Catalyst switches running

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−802.10.1q 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.−−−−− −−−−−−−−−−−−−−−−−− −−−−−−−−−− −−−−−−−−−− −−−−−− −−−−−− −−−−− −−−−−−−−−−−− 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 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: 10.1025−4094 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.10. cat6500# show vlan .3 Catalyst 6500 Switch The show interfaces interface−type module/port trunk command tells whether the port is trunking.

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