Virtual Private LAN Services
7750 SR OS Services Guide Page 329
2. Core Router Switching
a. All the core routers ('P' routers in IETF nomenclature) between PE-Router-A and PE-Rout-
er-B and PE-Router-C are Label Switch Routers (LSRs) that switch the packet based on the
transport (outer) label of the packet until the packet arrives at far-end PE-Router. All core
routers are unaware that this traffic is associated with a VPLS service.
3. PE-Router-C
a. PE-Router-C strips the transport label of the received packet to reveal the inner VC-label.
The VC-label identifies the VPLS service instance to which the packet belongs.
b. PE-Router-C learns the source MAC address in the packet and creates an entry in the FIB
table that associates the MAC address to PE-Router-A and the VC-label that PE-Router-A
signaled it for the VPLS service.
c. The destination MAC address in the packet is looked up in the FIB table for the VPLS in-
stance. Again, there are two possibilities: either the destination MAC address has already
been learned (known MAC address) or the destination MAC address has not been learned
on the access side of PE-Router-C (unknown MAC address).
Known MAC address (Figure 37)
d. If the destination MAC address has been learned by PE-Router-C, an existing entry in the
FIB table identifies the local access port and the IEEE 802.1Q tag to be added before send-
ing the packet to customer Location-C. The egress Q tag may be different than the ingress
Q tag.
Figure 5: Access Port Egress Packet Format and Lookup
B
PE C
B
Customer
Location A
IP/MPLS NETWORK
PE A
B
Pre-assigned and
signaled by PE ‘C’
PE B
Apply VC and
Tunnel Labels
Customer
Packet
Src
MAC
Dest
MAC
VC
Label X
Tunnel
Label
Customer
Packet
Src
MAC
Dest
MAC
VC
Label Y
Tunnel
Label
Pre-assigned and
signaled by PE ‘B’
B
PE C
B
Customer
Location A
IP/MPLS NETWORK
PE A
B
Pre-assigned and
signaled by PE ‘C’
PE B
Apply VC and
Tunnel Labels
Customer
Packet
Src
MAC
Dest
MAC
VC
Label X
Tunnel
Label
Customer
Packet
Src
MAC
Dest
MAC
VC
Label Y
Tunnel
Label
Pre-assigned and
signaled by PE ‘B’
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