802.1Q-in-Q Tunneling
Traditionally, VLANs accept not continued above the WAN boundary. VLANs in one campus
extend to a WAN bend router, but VLAN protocols are not acclimated on the WAN.
Today, several arising alternatives abide for the access of VLAN cartage beyond a WAN,
including 802.1Q-in-Q, Ethernet over MPLS (EoMPLS), and VLAN MPLS (VMPLS). While
these capacity are added applicative to the CCIE Account Provider certification, you should at least
know the abstraction of 802.1 Q-in-Q tunneling.
Also accepted as Q-in-Q or Layer 2 agreement tunneling, 802.1Q-in-Q allows an SP to preserve
802.1Q VLAN tags beyond a WAN service. By accomplishing so, VLANs absolutely amount multiple
geographically broadcast sites. Figure 2-5 shows the basal idea.
Figure 2-5 Q-in-Q: Basal Operation
C1-SW1
C2-SW1
SP:
Customer1: VLAN 5
Customer2: VLAN 6
VLANs 100-199
VLANs 100-500
C1-SW2
C2-SW2
SP-SW2
VLAN
ID 100
Data
VLAN
ID 6
Eth.
Header
VLAN
ID 100
Data
VLAN
ID 5
Eth.
Header
SP-SW1
VLAN
ID 100
Data
Eth.
Header
VLAN
ID 100
Data
Eth.
Header
VLAN
ID 100
Data
Eth.
Header
VLAN
ID 100
Data
Eth.
Header
The admission SP about-face takes the 802.1Q frame, and again tags anniversary anatomy entering the interface with
an added 802.1Q header. In this case, all of Customer1’s frames are tagged as VLAN 5 as they
pass over the WAN; Customer2’s frames are tagged with VLAN 6. After removing the tag at
egress, the chump about-face sees the aboriginal 802.1Q frame, and can adapt the VLAN ID
correctly. The accepting SP about-face (SP-SW2 in this case) can accumulate the assorted customers’ traffic
separate based on the added VLAN tags.
Using Q-in-Q, an SP can action VLAN services, alike back the barter use overlapping VLAN
IDs. Barter get added adaptability for arrangement architecture options, decidedly with busline Ethernet
services. Plus, CDP and VTP cartage passes clearly over the Q-in-Q service.