Answer
VPLS uses a dynamic virtual tunnel logical interface on a tunnel PIC to model traffic from a remote PE router site in a VPLS domain. All traffic coming from the remote site is treated as if it is coming over the virtual port that represents this remote site, for the purposes of Ethernet flooding, forwarding, and learning.
In this approach, an MPLS lookup based on the inner VPN label is done on a PE router in the CF chip or R-chip. The label is stripped and the Layer 2 Ethernet frame it contained is forwarded to a tunnel PIC. The tunnel PIC loops the packet back, then a lookup is performed based on Ethernet MAC addresses.
Drawbacks to this approach include creating a bottleneck at the tunnel PIC and requiring the PE router to perform two lookups.
By default, VPLS uses a tunnel PIC. If the no-tunnel-services statement is configured under a VPLS instance, it uses an LSI and does not require a tunnel PIC.
The current label numbering assignment is listed in the following table:
|
Services
|
Label Values
|
|
Reserved
|
0 - 15
|
|
LSI VPN
|
16 - 2047
|
|
LSP VPLS
|
2048 - 4095
|
|
Unassigned
|
4096 - 10,000
|
|
Static LSP
|
10,000-99,999
|
|
Global
|
100000-799999
|
|
Block Allocation
|
800000-899999
|
|
Per Intf
|
900000-999999
|
For more information, click Layer 2 VPNs and VPLS Feature Guide.