icnd22s02l01
TRANSCRIPT
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Extending Switched Networks withVirtual LANs
Introducing VLAN Operations
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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
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VLAN = Broadcast Domain = Logical Network (Subnet)
VLAN Overview
Segmentation
Flexibility
Security
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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
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VLAN Membership Modes
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802.1Q Trunking
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Importance of Native VLANs
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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, andbetween 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 configurationinformation
Maintains VLAN configuration consistency throughout a commonadministrative domain
Sends advertisements on trunk ports only
VTP Protocol Features
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Cannot create,change, or deleteVLANs
Forwardsadvertisements
Synchronizes
Not saved inNVRAM
Creates VLANs Modifies VLANs
Deletes VLANs
Sends and forwardsadvertisements
Synchronizes
Saved in NVRAM
Creates local VLANs only
Modifies local VLANs only
Deletes local VLANs only
Sends and forwardsadvertisements
Does notsynchronize
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
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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
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Summary
A VLAN permits a group of users to share a common broadcastdomain regardless of their physical location in theinternetwork. VLANs improve performance and security inswitched networks.
In a network, a Catalyst switch operates in a network like a
traditional bridge. Each VLAN configured on the switchimplements address learning, forwarding and filteringdecisions, and loop avoidance mechanisms.
Ports belonging to a VLAN are configured with a membershipmode that determines to which VLAN the ports belong. Catalyst
switches support two VLAN membership modes: static anddynamic.
The IEEE 802.1Q protocol is used to transport frames formultiple VLANs between switches and routers and for definingVLAN topologies.
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Summary (Cont.)
ISL is a Cisco proprietary protocol to transport multiple VLANsbetween switches and routers. ISL provides VLAN taggingcapabilities while maintaining full wire-speed performance.
VTP is a Layer 2 messaging protocol that maintains VLANconfiguration 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 VLANsare not propagated over the network until a managementdomain name is specified or learned.
VTP advertisements are sent throughout the managementdomain every 5 minutes or when there is a change. Theconfiguration revision number that is included in eachadvertisement identifies the most current information.
VTP pruning uses VLAN advertisements to determine when a
trunk connection is flooding traffic needlessly.
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