© 2006 cisco systems, inc. all rights reserved. icnd v2.3—2-1 extending switched networks with...
TRANSCRIPT
© 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—2-1
Extending Switched Networks with Virtual LANs
Introducing VLAN Operations
© 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—2-2
Outline
• Overview
• VLANs Defined
• VLAN Operation
• VLAN Membership Modes
• 802.1Q Trunking
• Inter-Switch Link Protocol and Encapsulation
• VLAN Trunking Protocol Features
• VTP Modes
• VTP Operations
• VTP Pruning
• Summary
© 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—2-3
VLAN = Broadcast Domain = Logical Network (Subnet)
VLAN Overview
• Segmentation
• Flexibility
• Security
© 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—2-4
• Each logical VLAN is like a separate physical bridge.
• VLANs can span across multiple switches.
• Trunks carry traffic for multiple VLANs.
• Trunks use special encapsulation to distinguish between different VLANs.
VLAN Operation
© 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—2-5
VLAN Membership Modes
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802.1Q Trunking
© 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—2-7
Importance of Native VLANs
© 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—2-8
802.1Q Frame
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Per VLAN Spanning Tree +
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• Performed with ASIC
• Not intrusive to client stations; ISL header not seen by client
• Effective between switches, and between routers and switches
ISL trunks enable VLANs across a backbone.
ISL Tagging
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ISL Encapsulation
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• Has a messaging system that advertises VLAN configuration information
• Maintains VLAN configuration consistency throughout a common administrative domain
• Sends advertisements on trunk ports only
VTP Protocol Features
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• Cannot create, change, or delete VLANs
• Forwards advertisements
• Synchronizes
• Not saved in NVRAM
•Creates VLANs
•Modifies VLANs
•Deletes VLANs
• Sends and forwards advertisements
• Synchronizes
• Saved in NVRAM
•Creates local VLANs only
•Modifies local VLANs only
•Deletes local VLANs only
• Sends and forwards advertisements
•Does not synchronize
• Saved in NVRAM
VTP Modes
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• VTP advertisements are sent as multicast frames.
• VTP servers and clients are synchronized to the latest revision number.
• VTP advertisements are sent every 5 minutes or when there is a change.
VTP Operation
© 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—2-15
• Increases available bandwidth by reducing unnecessary flooded traffic
• Example: Station A sends broadcast, and broadcast is flooded only toward any switch with ports assigned to the red VLAN
VTP Pruning
© 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—2-16
Summary
• A VLAN permits a group of users to share a common broadcast domain regardless of their physical location in the internetwork. VLANs improve performance and security in switched networks.
• In a network, a Catalyst switch operates in a network like a traditional bridge. Each VLAN configured on the switch implements address learning, forwarding and filtering decisions, and loop avoidance mechanisms.
• Ports belonging to a VLAN are configured with a membership mode that determines to which VLAN the ports belong. Catalyst switches support two VLAN membership modes: static and dynamic.
• The IEEE 802.1Q protocol is used to transport frames for multiple VLANs between switches and routers and for defining VLAN topologies.
© 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—2-17
Summary (Cont.)
• ISL is a Cisco proprietary protocol to transport multiple VLANs between switches and routers. ISL provides VLAN tagging capabilities while maintaining full wire-speed performance.
• VTP is a Layer 2 messaging protocol that maintains VLAN configuration consistency by managing the additions, deletions, and name changes of VLANs across networks.
• VTP operates in one of three modes: server, client, or transparent. The default VTP mode is server mode, but VLANs are not propagated over the network until a management domain name is specified or learned.
• VTP advertisements are sent throughout the management domain every 5 minutes or when there is a change. The configuration revision number that is included in each advertisement identifies the most current information.
• VTP pruning uses VLAN advertisements to determine when a trunk connection is flooding traffic needlessly.
© 2006 Cisco Systems, Inc. All rights reserved. ICND v2.3—2-18