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Service Provider Bridging | 957
Figure 46-6. TPID Match and First-byte Match on the E-Series TeraScale
TPID 0x8100 on E-Series TeraScale Systems
E-Series TeraScale treats TPID 0x8100 as a normal VLAN even when on the outer tag. E-Series TeraScale
makes forwarding decisions based strictly on the protocol type, without regard for whether the port is an
access port. Therefore, when the outer tag has TPID 0x8100, the system does not remove it from frames
egressing an access port. Still, although the frames cannot be decapsulated, the system is able to switch
them. In Figure 46-7, the frame originating from Building A is double tagged on egress at R4 and is
switched towards Building B, but is not decapsulated on egress at R2 because its TPID is 0x8181.
FTOS Behavior: The E-Series ExaScale and TeraScale forward frames with TPID 0x8100 even when
its own TPID is not 0x8100. This behavior is required to service ARP and PVST packets, which use
TPID 0x8100.
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E
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V
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C
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P
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O
V
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E
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VL
AN GREE
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, VLAN PURP
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VLAN G
REEN
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LAN
PU
RP
L
E
VL
AN
BLUE
VLAN RED
V
LAN R
E
D
VL
A
N
BLU
E
TPID
(0x8100)
PCP
CFI
(0)
VID
(VLAN Red)
TPID
(0x8100)
PCP
CFI
(0)
VID
(VLAN Red)
TPID
(0x9100)
PCP
CFI
(0)
VID
(VLAN Purple)
R4
Building A
Building B
R2-E-Series TeraScale
TPID: 0x9100
R3-E-Series TeraScale
TPID: 0x9100
R4-Non-Force10 System
TPID: 0x9100
R1-E-Series TeraScale
TPID: 0x9191
TPID 0x9191
Building C
Building D