SGS-6341-Series User Manual

20-80
SP network
P
PE1
PE2
CE1
CE2
Trunk connection
Trunk connection
Unsymmetrical
connection
Unsymmetrical
connection
This port on PE1 is enabled
Q-in-Q and belong to VLAN3
On the customer port
Trunk VLAN 200-300
On the customer port
Trunk VLAN 200-300
Customer
net
work 2
Customer network 1
This port on PE1 is enabled
Q-in-Q and belong to VLAN3
Figure 20-4: Dot1q-tunnel based Intern
etworking mode
As shown in above, after being enabled on the user port, dot1q-tunnel assigns each user an
SPVLAN identification (SPVID). Here the identification of user is 3. The same SPVID should
be assigned to the same network user on different PEs. When packet reaches PE1 from CE1,
it carries the VLAN tag 200-300 of the user internal network. Since the dot1q-tunnel function is
enabled, the user port on PE1 will add on the packet another VLAN tag, of which the ID is the
SPVID assigned to the user. Afterwards, the packet will only be transmitted in VLAN3 when
traveling in the ISP internet network while carrying two VLAN tags (the inner tag is added when
entering PE1, and the outer is SPVID), whereas the VLAN information of the user network is
open to the provider network. When the packet reaches PE2 and before being forwarded to
CE2 from the client port on PE2, the outer VLAN tag is removed, then the packet CE2 received
is absolutely identical to the one sent by CE1. For the user, the role the operator network plays
between PE1 and PE2, is to provide a reliable Layer 2 link.
The technology of Dot1q-tuunel provides the ISP internet the ability of supporting many client
VLANs by only one VLAN of themselves. Both the ISP internet and the clients can configure
their own VLAN independently.
It is obvious that the dot1q-tunnel function has got the following characteristics:
 Applicable through simple static configuration, no complex configuration or
maintenance is needed.
 Operators will only have to assign one SPVID for each user, which increases the
number of concurrent supportable users while the users has got the ultimate
freedom in selecting and managing the VLAN IDs (select within 1~4094 at users’
will).
User’s Manual of SGS-6341 series