© 2006 Cisco Systems, Inc. All rights reserved.BCMSN v Defining VLANs Implementing Trunks

© 2006 Cisco Systems, Inc. All rights reserved.BCMSN v Maintaining Specific VLAN Identification Specifically developed for multi-VLAN interswitch communications Places a unique identifier in each frame Functions at Layer 2

© 2006 Cisco Systems, Inc. All rights reserved.BCMSN v VLAN Trunking

© 2006 Cisco Systems, Inc. All rights reserved.BCMSN v Comparing ISL and 802.1Q ISL802.1Q ProprietaryNonproprietary EncapsulatedTagged Protocol independentProtocol dependent Encapsulates the old frame in a new frame Adds a field to the frame header

© 2006 Cisco Systems, Inc. All rights reserved.BCMSN v Trunking with ISL Is a Cisco proprietary protocol Supports PVST Uses an encapsulation process Does not modify the original frame

© 2006 Cisco Systems, Inc. All rights reserved.BCMSN v ISL Encapsulation

© 2006 Cisco Systems, Inc. All rights reserved.BCMSN v Trunking with 802.1Q An IEEE standard Adds a 4-byte tag to the original frame Additional tag includes a priority field Does not tag frames that belong to the native VLAN Supports Cisco IP telephony

© 2006 Cisco Systems, Inc. All rights reserved.BCMSN v The 802.1Q Tagging Process

© 2006 Cisco Systems, Inc. All rights reserved.BCMSN v Q Native VLAN Native VLAN frames are carried over the trunk link untagged.

© 2006 Cisco Systems, Inc. All rights reserved.BCMSN v VLAN Ranges VLAN Range Use 0, 4095 Reserved for system use only 1Cisco default 2–1001For Ethernet VLANs 1002–1005Cisco defaults for FDDI and Token Ring 1006–4094 Ethernet VLANs only, unusable on specific legacy platforms

© 2006 Cisco Systems, Inc. All rights reserved.BCMSN v Trunking Configuration Commands Configuring a Trunk switchport trunk switchport mode switchport nonegotiate Trunks can be configured statically or via DTP. DTP provides the ability to negotiate the trunking method.

© 2006 Cisco Systems, Inc. All rights reserved.BCMSN v Switchport Mode Interactions Dynamic Auto Dynamic Desirable TrunkAccess Dynamic Auto AccessTrunk Access Dynamic Desirable Trunk Access Trunk Not recommended Access Not recommended Access Note: Table assumes DTP is enabled at both ends. show dtp interface – to determine current setting

© 2006 Cisco Systems, Inc. All rights reserved.BCMSN v How to Configure Trunking 1. Enter interface configuration mode. 2. Shut down interface. 3. Select the encapsulation (802.1Q or ISL). 4. Configure the interface as a Layer 2 trunk. 5. Specify the trunking native VLAN (for 802.1Q). 6. Configure the allowable VLANs for this trunk. 7. Use the no shutdown command on the interface to activate the trunking process. 8. Verify the trunk configuration.

© 2006 Cisco Systems, Inc. All rights reserved.BCMSN v Q Trunk Configuration Switch(config)#interface fastethernet 5/8 Switch(config-if)#shutdown Switch(config-if)#switchport trunk encapsulation dot1q Switch(config-if)#switchport trunk allowed vlan 1,5,11, Switch(config-if)#switchport mode trunk Switch(config-if)#switchport trunk native vlan 99 Switch(config-if)#switchport nonegotiate Switch(config-if)#no shutdown

© 2006 Cisco Systems, Inc. All rights reserved.BCMSN v Verifying the 802.1Q Configuration Switch#show running-config interface {fastethernet | gigabitethernet} slot/port Switch#show interfaces [fastethernet | gigabitethernet] slot/port [ switchport | trunk ] Switch#show interfaces fastEthernet 5/8 switchport Name: fa5/8 Switchport: Enabled Administrative Mode: trunk Operational Mode: trunk Administrative Trunking Encapsulation: dot1q Operational Trunking Encapsulation: dot1q Negotiation of Trunking: Off Access Mode VLAN: 1 (default) Trunking Native Mode VLAN: 99 (trunk_only) Trunking VLANs Enabled: 1,5,11, Pruning VLANs Enabled:

© 2006 Cisco Systems, Inc. All rights reserved.BCMSN v Verifying a 802.1Q Dynamic Trunk Link Switch#show running-config interface fastethernet 5/8 Building configuration... Current configuration: ! interface FastEthernet5/8 switchport mode dynamic desirable switchport trunk encapsulation dot1q Switch#show interfaces fastethernet 5/8 trunk Port Mode Encapsulation Status Native vlan Fa5/8 desirable 802.1q trunking 99 Port Vlans allowed on trunk Fa5/8 1,5,11, Port Vlans allowed and active in management domain Fa5/8 1,5, Port Vlans in spanning tree forwarding state and not pruned Fa5/8 1,5,

© 2006 Cisco Systems, Inc. All rights reserved.BCMSN v ISL Trunk Configuration Switch(config)#interface fastethernet 2/1 Switch(config-if)#shutdown Switch(config-if)#switchport trunk encapsulation isl Switch(config-if)#switchport trunk allowed vlan 1-5, Switch(config-if)#switchport mode trunk Switch(config-if)#switchport nonegotiate Switch(config-if)#no shutdown

© 2006 Cisco Systems, Inc. All rights reserved.BCMSN v Verifying ISL Trunking Switch#show running-config interface {fastethernet | gigabitethernet} slot/port Switch#show interfaces [fastethernet | gigabitethernet] slot/port [ switchport | trunk ] Switch#show interfaces fastethernet 2/1 trunk Port Mode Encapsulation Status Native VLAN Fa2/1 trunk isl trunking 99 Port VLANs allowed on trunk Fa2/1 1-5, Port VLANs allowed and active in management domain Fa2/1 1-2, Port VLANs in spanning tree forwarding state and not pruned Fa2/1 1-2,

© 2006 Cisco Systems, Inc. All rights reserved.BCMSN v Summary Trunk links carry traffic from multiple VLANs. ISL is Cisco proprietary and encapsulates the Layer 2 frames Q is an IEEE standard for trunking, which implements a 4-byte tag. The 802.1Q native VLANs forward frames without the tag. VLAN numbers have specific ranges and purposes. Various commands are used to configure and verify ISL and 802.1Q trunk links. Allow only required VLANs over the trunk.

© 2006 Cisco Systems, Inc. All rights reserved.BCMSN v