Cisco Q-in-Q Configuration Example:
Cisco switches(not all
of them) supports IEEE 802.1Q tunneling(Q-in-Q) and Layer 2 protocol
tunneling features to carry customer’s multiple vlans across the service
provider’s L2 backbone.
In this example, we will do Q-in-Q
configuration.
Here is the topology for this
example:
Q-in-Q configuration
on PE Switch-1:
interface GigabitEthernet0/2
port-type nni
switchport access
vlan 100
switchport mode
dot1q-tunnel
Q-in-Q configuration
on PE Switch-2:
interface GigabitEthernet0/2
port-type nni
switchport access
vlan 100
switchport mode
dot1q-tunnel
Uplink Port Configuration
of CE Switch-1
interface FastEthernet3
switchport mode trunk
interface Vlan10
ip address 10.10.10.1
255.255.255.0
interface Vlan20
ip address 20.20.20.1
255.255.255.0
Uplink Port Configuration
of CE Switch-2
interface FastEthernet3
switchport mode trunk
interface Vlan10
ip address 10.10.10.2
255.255.255.0
interface Vlan20
ip address 20.20.20.2
255.255.255.0
Lets test the
L2TP(Layer2 Tunneling Protocol) configuration:
CE –Switch-1#ping 10.10.10.2
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.10.10.2, timeout is 2
seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max =
1/1/4 ms
We see that connection
works.
Lets increase the size
of the packet:
CE –Switch-1#ping 10.10.10.2 size 1496 df-bit
Type escape sequence to abort.
Sending 5, 1496-byte ICMP Echos to 10.10.10.2, timeout is 2
seconds:
Packet sent with the DF bit set
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max =
1/2/4 ms
It’s ok again..
Lets increase the size 1-byte more..
CE –Switch-1#ping 10.10.10.2 size 1497 df-bit
Type escape sequence to abort.
Sending 5, 1497-byte ICMP Echos to 10.10.10.2, timeout is 2
seconds:
Packet sent with the DF bit set
.....
Success rate is 0 percent (0/5)
It doesn’t
work.Because PE switch adds a new 802.1q
header.The size of this heades is 4-byte.So, the MTU must be increased at all switches of the Service Provider.New value must be 1504 or more.
