VLAN的讲解与配置

–Supports Cisco
The 802.1Q Tagging Process
802.1Q Native VLAN
Native VLAN frames are carried over the trunk link untagged.
VLAN Ranges
VLAN Range 0, 4095 1 2–1001 1002– 1005
–Allocate one IP subnet per VLAN.
Interconnection Technologies
Technology Use
Fast Ethernet
Connects end-user devices to the access layer switch
Gigabit Ethernet
Verifying the 802.1Q Configuration
Switch#show running-config interface {fastethernet | gigabitethernet} slot/port
Switch#show interfaces [fastethernet | gigabitethernet] slot/port [ switchport | trunk ]
Trunk
Access
Dynamic Desirable
Trunk
Trunk
Trunk
Access
Trunk Access
Not
Trunk
Trunk
Trunk
recommende
Note: Table assumes DTP is enabled at bothdends.
• show dtp interface – to deterNmoint e current setting
–switchport trunk –switchport mode –switchport nonegotiate
Switchport Mode Interactions
Dynamic Auto
Dynamic Desirable
Trunk
Access
Dynamic Auto
Access
Trunk
Determining Equipment and Cabling Needs
Each link provides adequate bandwidth for traffic aggregating over that link.
VLANs and the Logical Network
Network Traffic Types
Access Access recommend Access
ed
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
Traffic types to consider:
• Network management • IP telephony • Multicast • Normal data • Scavenger class
Traffic Path for IP Telephony
Consider complete traffic path when placing equipment and configuring VLANs.
switchport mode dynamic desirable switchport trunk encapsulation dot1q
Switch#show interfaces fastethernet 5/8 trunk
Port
Mode
Native vlan
Encapsulation Status
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)
–Management and support challenges
Scalable Network Addressing
IT, Human Resources Sales, Marketing
Finance, Accounting
–Allocate IP address spaces in contiguous blocks.
802.1Q). 6. Configure the allowable VLANs for this trunk. 7. Use the no shutdown command on the
interface to activate the trunking process.
802.1Q Trunk Configuration
Traffic Path for IP Multicast
Consider complete traffic path when placing equipment and configuring VLANs.
Summary
• Poorly designed networks can lead to large broadcast domains.
Fa5/8
desirable 802.1q
trunking
99
Port Fa5/8
Vlans allowed on trunk 1,5,11,1002-1005
Port Fa5/8
Vlans allowed and active in management domain 1,5,1002-1005
Port pruned
ISL Encapsulation
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
Issues in a Poorly Designed Network
–Unbounded failure domains
–Large broadcast domains
–Large amount of unknown MAC unicast traffic
– Unbounded multicast traffic
• A hierarchical IP addressing scheme scales well in the Campus Infrastructure module.
• The interconnection technology used depends on the amount of traffic the link must carry.
Switch(config)#interface fastethernet 5/8 Switch(config-if)#shutdown Switch(config-if)#switchport trunk encapsulation dot1q Switch(config-if)#switchport trunk allowed vlan 1,5,11,1002-1005 Switch(config-if)#switchport mode trunk Switch(config-if)#switchport trunk native vlan 99 Switch(config-if)#switchport nonegotiate Switch(config-if)#no shutdown
• Separate voice and data VLANs are
Maintaining Specific VLAN Identification
• Specifically developed for multi-VLAN interswitch communications
• Places a unique identifier in each frame • Functions at Layer 2
Access to distribution switch, high-use servers
10-Gigabit High-speed switch Ethernet to switch links,
bቤተ መጻሕፍቲ ባይዱckbones
EtherChan High-speed switch
nel
to switch links,
Tagged Protocol dependent
Adds a field to the frame header
Trunking with ISL
–Is a Cisco proprietary protocol
–Supports PVST –Uses an
encapsulation process –Does not modify the original frame
Trunking VLANs Enabled: 1,5,11,1002-1005
Pruning VLANs Enabled: 2-1001
...
Verifying a 802.1Q Dynamic Trunk Link
Switch#show running-config interface fastethernet 5/8 Building configuration... Current configuration: ! interface FastEthernet5/8
VLAN Trunking
Comparing ISL and 802.1Q
ISL Proprietary Encapsulated Protocol independent Encapsulates the old frame in a new frame
802.1Q Nonproprietary
Vlans in spanning tree forwarding state and not
• Select the best equipment, cabling, and interconnection technologies to connect devices.
• VLANs should map to the IP hierarchy for the Campus Infrastructure module.
Trunking Configuration Commands
• Trunks can be configured statically or via DTP. • DTP provides the ability to negotiate the trunking method.
Configuring a Trunk
1006– 4094
Use
Reserved for system use only Cisco default For Ethernet VLANs Cisco defaults for FDDI and Token Ring Ethernet VLANs only, unusable on specific legacy platforms