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Defining VLANs Implementing Trunks. Maintaining Specific VLAN Identification Specifically developed for multi-VLAN interswitch communications Places a.

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Presentation on theme: "Defining VLANs Implementing Trunks. Maintaining Specific VLAN Identification Specifically developed for multi-VLAN interswitch communications Places a."— Presentation transcript:

1 Defining VLANs Implementing Trunks

2 Maintaining Specific VLAN Identification Specifically developed for multi-VLAN interswitch communications Places a unique identifier in each frame( 每个帧有唯 一标识 ) Functions at Layer 2

3 VLAN Trunking

4 Comparing ISL and 802.1Q ISL802.1Q Proprietary( 私有 )Nonproprietary (公有) Encapsulated (封装式) Tagged (标记式) Protocol independentProtocol dependent Encapsulates the old frame in a new frame Adds a field to the frame header

5 Trunking with ISL Is a Cisco proprietary protocol Supports PVST Uses an encapsulation process Does not modify the original frame

6 ISL Encapsulation

7 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

8 The 802.1Q Tagging Process

9 802.1Q Native VLAN Native VLAN frames are carried over the trunk link untagged. (本征 vlan 不会标记就能穿越干道)

10 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 透明模式的交换机可使用扩展的 vlan 号(扩展 vlan 不在 vlan 数据库 中,不能共享通告。如果把透明改回服务器或客户,得把扩展 vlan 删除)

11 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. ( DTP 思科动态中继协议用于自动协商中继模式, 并选择适当的封装协 议)

12 Trunking Configuration Commands switchport mode trunk (永久成为 trunk ) dynamic desirable (默认模式,端口主动尝试 将链路变为 trunk ) dynamic auto (被动模式仅当远端设备请求式 才成为 trunk ) switchport nonegotiate (关闭 dtp 自动协商) switchport trunk encapsulation {isl | dot1q |negotiate (默认) } switchport trunk allowed {all | vlan x} (允许 vlan 通行)

13 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

14 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.

15 802.1Q 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

16 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:

17 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,

18 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

19 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,

20 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.

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