Virtual Private LAN Services
7750 SR OS Services Guide Page 421
Figure 58: Access Port Ingress Packet Format and Lookup
b. PE-Router-A learns the source MAC address in the packet and creates an entry in the FIB
table that associates the MAC address to the service access point (SAP) on which it was
received.
c. The destination MAC address in the packet is looked up in the FIB table for the VPLS in-
stance. There are two possibilities: either the destination MAC address has already been
learned (known MAC address) or the destination MAC address is not yet learned (unknown
MAC address).
For a Known MAC Address (Figure 59):
d. If the destination MAC address has already been learned by PE-Router-A, an existing entry
in the FIB table identifies the far-end PE-router and the service VC-label (inner label) to
be used before sending the packet to far-end PE-Router-C.
e. PE-Router-A chooses a transport LSP to send the customer packets to PE-Router-C. The
customer packet is sent on this LSP once the IEEE 802.1Q tag is stripped and the service
VC-label (inner label) and the transport label (outer label) are added to the packet.
For an Unknown MAC Address (Figure 59):
f. If the destination MAC address has not been learned, PE-Router-A will flood the packet to
both PE-Router-B and PE-Router-C that are participating in the service by using the VC-
labels that each PE-Router previously signaled for the VPLS instance. Note that the packet
is not sent to PE-Router-D since this VPLS service does not exist on that PE-router.
PE A
Customer
Location A
IP/MPLS Network
Ingress look-up based on
access port or port/VLAN-ID.
Dest
MAC
Src
MAC
VLAN
ID
Customer
Packet
OSSG202
B
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