PLANET XGS3-24040 - Manual (Page 122)

Chapter 14 VLAN Configuration
14-11
14.2.4 GVRP Troubleshooting
The GARP counter setting in for Trunk ports in both ends of Trunk link must be the same, otherwise GVRP will
not work properly. It is recommended to avoid enabling GVRP and RSTP at the same time in switch. If GVRP
is to be enabled, RSTP function for the ports must be disabled first.
14.3 Dot1q-tunnel Configuration
14.3.1 Introduction to Dot1q-tunnel
Dot1q-tunnel is also called QinQ (802.1Q-in-802.1Q), which is an expansion of 802.1Q. Its dominating idea is
encapsulating the customer VLAN tag (CVLAN tag) to the service provider VLAN tag (SPVLAN tag). Carrying
the two VLAN tags the packet is transmitted through the backbone network of the ISP internet, so to provide a
simple layer-2 tunnel for the users. It is simple and easy to manage, applicable only by static configuration,
and especially adaptive to small office network or small scale metropolitan area network using layer-3 switch
as backbone equipment.
Figure 1-5 Dot1q-tunnel based Internetworking 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. Same SPVID should be assigned for 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 receives 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.
SP networks
P
PE1
PE2
CE1
CE2
Trunk connection
Trunk connection
Unsymmetrical
connection
Unsymmetrical
connection
Customer
networks1
Customer
networks2
On the customer port
Trunk VLAN 200-300
This port on PE1 is enabled
QinQ and belong to VLAN3
On the customer port
Trunk VLAN 200-300
This port on PE1 is enabled
QinQ and belong to VLAN3