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Network Administration: Configure VLAN and InterVLAN Routing

Lab Environment:

  • Router: Cisco 2951
  • Switch: Cisco C3750G PoE
  • 2 VLANs

Method 1: router-on-a-stick

Topology: C3750G (GigabitEthernet3/0/1) -- CISCO2951(GigabitEthernet0/1) -- INTERNET(GigabitEthernet0/0)

On CISCO2951:

CISCO2951(config)#interface GigabitEthernet 0/0
CISCO2951(config-if)#no shutdown
CISCO2951(config-if)#speed 1000
CISCO2951(config-if)#duplex full
CISCO2951(config-if)#exit

CISCO2951(config)#interface GigabitEthernet 0/0.10
CISCO2951(config-subif)#encapsulation dot1Q 10
CISCO2951(config-subif)#ip address 192.168.10.1 255.255.255.0
CISCO2951(config-subif)#exit

CISCO2951(config)#interface GigabitEthernet 0/0.20
CISCO2951(config-subif)#encapsulation dot1Q 20                 
CISCO2951(config-subif)#ip address 192.168.20.1 255.255.255.0

On C3750G:

C3750G(config)#interface GigabitEthernet 3/0/1
C3750G(config-if)#switchport mode trunk
C3750G(config-if)#switchport trunk encapsulation dot1q
C3750G(config-if)#no shutdown
C3750G(config-if)#speed 1000
C3750G(config-if)#duplex full
C3750G(config-if)#exit

C3750G(config)#vlan 10
C3750G(config-vlan)#name VLAN10
C3750G(config-vlan)#exit
C3750G(config)#vlan 20
C3750G(config-vlan)#name VLAN20
C3750G(config-vlan)#exit

# Assign ports to the VLANs as needed:
C3750G(config)#interface GigabitEthernet 3/0/2
C3750G(config-if)#switchport mode access
C3750G(config-if)#switchport access vlan 10
C3750G(config-if)#no shutdown
C3750G(config-if)#speed 1000
C3750G(config-if)#duplex full
C3750G(config-if)#exit

C3750G(config)#interface GigabitEthernet 3/0/3
C3750G(config-if)#switchport mode access
C3750G(config-if)#switchport access vlan 20
C3750G(config-if)#no shutdown
C3750G(config-if)#speed 1000
C3750G(config-if)#duplex full
C3750G(config-if)#exit

Method 2: SVI (Switch Virtual Interface) and InterVLAN routing on C3750G switch.

Topology: C3750G (GigabitEthernet3/0/1) -- CISCO2951(GigabitEthernet0/1) -- INTERNET(GigabitEthernet0/0)

CISCO2951 Configs:

# Configure GigabitEthernet 0/0 (connected to ISP's device for internet access) to use DHCP.
CISCO2951(config)#interface GigabitEthernet 0/0
CISCO2951(config-if)#ip address dhcp
CISCO2951(config-if)#ip nat outside
CISCO2951(config-if)#ip virtual-reassembly in
CISCO2951(config-if)#no shutdown
CISCO2951(config-if)#speed 1000
CISCO2951(config-if)#duplex full
CISCO2951(config-if)#exit

# Configure GigabitEthernet0/1 (connected to C3750G).
CISCO2951(config)#interface GigabitEthernet 0/1
CISCO2951(config-if)#ip address 192.168.0.1 255.255.255.0
CISCO2951(config-if)#ip access-group NAT_ACL in
CISCO2951(config-if)#ip nat inside
CISCO2951(config-if)#ip virtual-reassembly in
CISCO2951(config-if)#no shutdown
CISCO2951(config-if)#speed 1000
CISCO2951(config-if)#duplex full
CISCO2951(config-if)#exit

# Configure ACL and NAT.
CISCO2951(config)#ip dns server
CISCO2951(config)#ip name-server 1.1.1.1
CISCO2951(config)#ip access-list extended NAT_ACL
CISCO2951-K9(config-ext-nacl)#permit ip 192.168.0.0 0.0.0.255 any
CISCO2951-K9(config-ext-nacl)#exit
CISCO2951(config)#ip nat inside source list NAT_ACL interface GigabitEthernet0/0 overload

# Enable routing and configure EIGRP (optional, depending on your configs)
CISCO2951(config)#ip routing
CISCO2951(config)#router eigrp 100
CISCO2951(config-router)#network 192.168.0.0 0.0.0.255

C3750G Configs:

# Enable routing:
C3750G(config)#ip routing

# Configure cef (Cisco Express Forwarding
) for better performance:
C3750G(config)#ip cef distributed
C3750G(config)#ip cef optimize neighbor resolution

#Configure DNS
C3750G(config)#ip domain-lookup
C3750G(config)#ip name-server 192.168.0.1

# Enable spanning-tree protocol.
C3750G(config)#spanning-tree mode rapid-pvst

# Configure VLANs
C3750G(config)#vlan 10
C3750G(config-vlan)#name VLAN10
C3750G(config-vlan)#exit
C3750G(config)#vlan 20
C3750G(config-vlan)#name VLAN20
C3750G(config-vlan)#exit

C3750G(config)#interface vlan 10
C3750G(config-if)#ip address 192.168.10.1 255.255.255.0
C3750G(config-if)#ip helper-address 192.168.0.1
C3750G(config)#interface vlan 20
C3750G(config-if)#ip address 192.168.20.1 255.255.255.0
C3750G(config-if)#ip helper-address 192.168.0.1

# Configure trunk port
C3750G(config)#interface GigabitEthernet 3/0/1
C3750G(config-if)#no switchport
C3750G(config-if)#ip address 192.168.0.2 255.255.255.0
C3750G(config-if)#no shutdown
C3750G(config-if)#speed 1000
C3750G(config-if)#duplex full

# Configure default route.
C3750G(config)#ip route 0.0.0.0 0.0.0.0 GigabitEthernet 3/0/1

# Assign ports to VLANs
C3750G(config)#interface range GigabitEthernet 3/0/2 - 5
C3750G(config-if-range)#switchport access vlan 10
C3750G(config-if-range)#switchport mode access
C3750G(config-if-range)#speed 1000
C3750G(config-if-range)#duplex full
C3750G(config-if-range)#no shut

C3750G(config)#interface range GigabitEthernet 3/0/6 - 12
C3750G(config-if-range)#switchport access vlan 20
C3750G(config-if-range)#switchport mode access
C3750G(config-if-range)#speed 1000
C3750G(config-if-range)#duplex full
C3750G(config-if-range)#no shut