H3C Technologies H3C S12500-X Series Switches - Manual (Page 294)

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packet is forwarded to the correct VSI. The outer label is the public LSP or MPLS TE tunnel label,
which makes sure the packet is correctly forwarded to the remote PE.
• VPLS instance—A customer network might include multiple geographically dispersed sites (such as
site 1 and site 3 in
Figure 74 .) The service provider uses VPLS to connect all the sites to create a
single Layer 2 VPN, which is referred to as a "VPLS instance." Sites in different VPLS instances
cannot communicate with each other at Layer 2.
• VSI—A virtual switch instance provides Layer 2 switching services for a VPLS instance on a PE. A VSI
acts as a virtual switch that has all the functions of a conventional Ethernet switch, including source
MAC address learning, MAC address aging, and flooding. VPLS uses VSIs to forward Layer 2 data
packets in VPLS instances.
VPLS implementation
Creating a PW
PEs use PWs to forward packets among VPN sites. PWs include static PWs, LDP PWs, BGP PWs, and
BGP auto-discovery LDP PWs.
• Static PW
To create a static PW, specify the address of the remote PE, the incoming label, and the outgoing
label.
• LDP PW
To create an LDP PW, specify the address of the remote PE, and use LDP to advertise the PW-label
binding to the remote PE. After the two PEs receive the PW-label binding from each other, they
establish an LDP PW. The FEC type in the LDP message is PWid FEC Element that includes the PW
ID field (FEC 128). The PW ID identifies the PW bound to the PW label.
• BGP PW
To create a BGP PW, BGP advertises label block information to the remote PE. After the two PEs
receive label block information from each other, they use the label block information to calculate
the incoming and outgoing labels and create the BGP PW. A PE also uses the received label block
information to automatically find the remote PE.
• BGP auto-discovery LDP PW
To create a BGP auto-discovery LDP PW, a PE uses BGP to automatically find the remote PE, and
uses LDP to advertise the PW-label binding to the remote PE. After the two PEs receive the PW-label
binding from each other, they establish a BGP auto-discovery LDP PW.
The information advertised by BGP includes the ID (for example, LSR ID) and VPLS ID of the
advertising PE. The receiving PE compares the received VPLS ID with its own VPLS ID. If the two
VPLS IDs are identical, the two PEs use LDP to establish a PW. If not, the PEs do not establish a PW.
The FEC type in the LDP message is Generalized PWid FEC Element (FEC 129), which contains the
VPLS ID, Source Attachment Individual Identifier (SAII), and Target Attachment Individual Identifier
(TAII). The SAII is the LSR ID of the advertising PE. The TAII identifies the remote PE and is advertised
by the remote PE. VPLS ID+SAII+TAII uniquely identifies a PW in a VPLS instance.
MAC address learning, aging, and withdrawal
VPLS provides reachability through source MAC learning. A PE maintains a MAC address table for each
VSI.
As shown in
Figure 75 , a PE learns source MAC addresses in the following ways:
• Learning the source MAC addresses of directly connected sites: