VLAN

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VLANs - Virtual Local Area Networks - are a way to divide a physical network into multiple, separated LANS.

To configure a VLAN you must on a switch set:

• what ports belong to a VLAN
• how to manage traffic between different switches: trunk
• how to manage communication between different VLANs: routing (needs a layer 3 device)

Every end device must be configured:

• IP coherent with VLAN
• Default Gateway = IP of VLAN
  ES: VLAN 30: 192.168.30.xx

Inter-VLAN routing

This needs a layer 3 device, there are 2 options:

Legacy: IP router - multiple ‘access’ links

One router with multiple links, one for every VLAN. This router routes between these VLANS.

Switch:

s1(config)#vlan 10
s1(config-vlan)#vlan 30
exit
interface f0/11
switchport access vlan 10
interface f0/4 ecc

Router:

# Setting up VLAN 30
interface f00
ip address 172.17.30.1 255.255.255.0
no shutdown

Router-on-a-stick:

Router connected with a single link to a switch connected to multiple VLANs.

# associating sub interface with VLAN 10
r1(config)#interface gigabitEthernet 0/0.10
r1(config-subif)#encapsulation dot1Q 10
 ip address 192.168.10.1 255.255.255.0
 
interface gigabitEthernet 0/0.20
 encapsulation dot1Q 20
 ip address 192.168.20.1 255.255.255.0

Multilayer Switch - Layer 3 Switch

This is a more modern approach.

interface vlan 10
 ip address 192.168.10.1 255.255.255.0
 
interface vlan 20
 ip address 192.168.20.1 255.255.255.0
 
ip routing

CISCO

enable
configure terminal
 
vlan 10
 name AMMINISTRAZIONE
 
vlan 20
 name TECNICI
 
# setting which ports belong to which VLAN:
interface fastEthernet 0/1
 switchport mode access
 switchport access vlan 10
 
interface fastEthernet 0/2
 switchport mode access
 switchport access vlan 20
 
# Setting a trunk: multiple VLANs working on the same interface
interface gigabitEthernet 0/1
 switchport mode trunk
 # per consentire solo alcune vlan:
 switchport mode trunk allowed 10,20
 
 
show vlan brief
show interface trunk