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952 | Service Provider Bridging
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In at the access point of a VLAN-stacking network, service providers add a VLAN tag, the S-Tag, to each
frame before the 802.1Q tag. From this point, the frame is double-tagged. The service provider uses the
S-Tag, to forward the frame traffic across its network. At the egress edge, the provider removes the S-Tag,
so that the customer receives the frame in its original condition (Figure 46-1).
Figure 46-1. VLAN Stacking in a Service Provider Network
Important Points to Remember
• Interfaces that are members of the Default VLAN and are configured as VLAN-Stack access or trunk
ports do not switch untagged traffic. To switch traffic, these interfaces must be added to a non-default
VLAN-Stack-enabled VLAN.
• Dell Force10 cautions against using the same MAC address on different customer VLANs, on the
same VLAN-Stack VLAN.
• You can ping across a trunk port only if both systems on the link are an E-Series. You cannot ping
across the link if one or both of the systems is a C-Series or S-Series.
• This limitation becomes relevant if you enable the port as a multi-purpose port (carrying single-tagged
and double-tagged traffic).
VLAN
300
VLAN100
I
N
T
E
R
N
E
T
S
E
R
V
R
R
I
C
E
P
R
O
V
I
D
E
R
w
R
/
V
L
A
N
S
T
A
T
T
C
K
I
N
G
VL
AN
200
V
LAN
1
0
0
VLAN 100
V
L
A
N
1
00
tagged 100
tagged 100
TPID
(0x8100)
PCP
CFI
(0)
VID
(VLAN Red)
TPID
(0x9100)
PCP
DEI
VID
(VLAN 300)
access port
trunk port