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Chapter 6 VLAN (Code (Show results (S1(config-if)# do show vlan brief…
Chapter 6 VLAN
Code
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show vlan brief
The show vlan brief command displays the VLAN assignment and membership type for all switch ports.
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Types of VLAN
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Default VLAN
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VLAN 1 has all the features of any VLAN, except it cannot be renamed or deleted. By default, all Layer 2 control traffic is associated with VLAN 1.
Native VLAN
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The 802.1Q trunk port places untagged traffic on the native VLAN, which by default is VLAN 1.
it is not unusual to dedicate a fixed VLAN to serve the role of the native VLAN for all trunk ports in the switched domain.
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Theory
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VLANs enable the implementation of access and security policies according to specific groupings of users.
Each switch port can be assigned to only one VLAN (with the exception of a port connected to an IP phone or to another switch).
VLAN Trunks
VLAN trunks allow all VLAN traffic to propagate between switches, so that devices which are in the same VLAN,
Tagging
The standard Ethernet frame header does not contain information about the VLAN to which the frame belongs; thus, when Ethernet frames are placed on a trunk, information about the VLANs to which they belong must be added. This process, called tagging, is accomplished by using the IEEE 802.1Q header, specified in the IEEE 802.1Q standard.
Troubleshooting
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Allowed VLANs on trunks - The list of allowed VLANs on a trunk has not been updated with the current VLAN trunking requirements.
Causes lost traffic, correct list by adding VLANS to trunk
Troubleshooting
Each VLAN must correspond to a unique IP subnet. If two devices in the same VLAN have different subnet addresses, they cannot communicate.
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Inter-vlan Routing
Types
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Router-on-stick
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Subinterfaces are configured for different subnets corresponding to their VLAN assignment to facilitate logical routing.
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Code
Interface g0/0.10
Encapsulation dot1q 10
Interface g0/0.20
Encapsulation dot1q 20
Interface g0/0
No shutdown
Sub-interfaces
Subinterfaces are software-based virtual interfaces that are assigned to physical interfaces. Each subinterface is configured independently with its own IP address and prefix length
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