Vlans Cheat Sheet
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1VLAN
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Trunk Encapsulation
Trunk Types
802.1Q
ISL
26
6
6
2
4
ISL
Dest
Source
Header Size
4 bytes
26 bytes
ISL
Type
FCS
Header
MAC
MAC
Trailer Size
N/A
4 bytes
Dest
Source
Standard
IEEE
Cisco
Untagged
Type
MAC
MAC
Maximum VLANs
4094
1000
Dest
Source
802.1Q
802.1Q
Type
VLAN Numbers
MAC
MAC
0 Reserved
1004 fdnet
6
6
4
2
VLAN Creation
1 default
1005 trnet
1002 fddi-default
1006-4094 Extended
Switch(config)#
vlan 100
Switch(config-vlan)#
name Engineering
1003 tr
4095 Reserved
Access Port Configuration
Terminology
Trunking
Switch(config-if)#
switchport mode access
Carrying multiple VLANs over the same
Switch(config-if)#
switchport nonegotiate
physical connection
Switch(config-if)#
switchport access vlan 100
Switch(config-if)#
switchport voice vlan 150
Native VLAN
By default, frames in this VLAN are untagged
Trunk Port Configuration
when sent across a trunk
Switch(config-if)#
switchport mode trunk
Access VLAN
Switch(config-if)#
switchport trunk encapsulation dot1q
The VLAN to which an access port is assigned
Switch(config-if)#
switchport trunk allowed vlan 10,20-30
Voice VLAN
Switch(config-if)#
switchport trunk native vlan 10
If configured, enables minimal trunking to
support voice traffic in addition to data traffic
SVI Configuration
on an access port
Switch(config)#
interface vlan100
Dynamic Trunking Protocol (DTP)
Switch(config-if)#
ip address 192.168.100.1 255.255.255.0
Can be used to automatically establish trunks
between capable ports (insecure)
VLAN Trunking Protocol (VTP)
Switched Virtual Interface (SVI)
Domain
A virtual interface which provides a routed
Common to all switches participating in VTP
gateway into and out of a VLAN
Server Mode
Generates and propagates VTP advertisements to clients;
Switch Port Modes
default mode on unconfigured switches
trunk
Client Mode
Forms an unconditional trunk
Receives and forwards advertisements from servers; VLANs
dynamic desirable
cannot be manually configured on switches in client mode
Attempts to negotiate a trunk with the far end
Transparent Mode
dynamic auto
Forwards advertisements but does not participate in VTP;
Forms a trunk only if requested by the far end
VLANs must be configured manually
access
Pruning
Will never form a trunk
VLANs not having any access ports on an end switch are
Troubleshooting
removed from the trunk to reduce flooded traffic
show vlan
VTP Configuration
show interface [status | switchport]
Switch(config)#
vtp mode {server | client | transparent}
show interface trunk
vtp domain <name>
Switch(config)#
vtp password <passsword>
Switch(config)#
show vtp status
Switch(config)#
vtp version {1 | 2}
Switch(config)#
vtp pruning
show vtp password
by Jeremy Stretch
v2.0
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