Cisco 7604 Configuration Manual page 353

Chapter 24 Configuring PFC3BXL and PFC3B Mode Multiprotocol Label Switching
The MSFC on the supervisor engine performs Layer 3 control-plane functions, including address
resolution and routing protocols. The MSFC processes information from the Routing and Label
Distribution Protocols and builds the IP forwarding (FIB) table and the label forwarding (LFIB) table.
The MSFC distributes the information in both tables to the PFC3BXL or PFC3B.
The PFC3BXL or PFC3B receives the information and creates its own copies of the FIB and LFIB tables.
Together, these tables comprise the FIB TCAM. The DFC looks up incoming IP packets and labeled
packets against the FIB TCAM table. The lookup result is the pointer to a particular adjacency entry. It is the
adjacency entry that contains appropriate information for label pushing (for IP to MPLS path), label swapping
(for MPLS to MPLS path), label popping (for MPLS to IP path), and encapsulation.
Figure 24-2
switching. Routing protocol generates a routing information base (RIB) that is used for forwarding IP and
MPLS data packets. For Cisco Express Forwarding (CEF), necessary routing information from the RIB is
extracted and built into a forwarding information base (FIB). The label distribution protocol (LDP) obtains
routes from the RIB and distributes the label across a label switch path to build a label forwarding information
base (LFIB) in each of the LSRs and LERs.
Figure 24-2 MPLS Forwarding, Control and Data Planes
IP forwarding
IP to MPLS
At the ingress to the MPLS network, the PFC3BXL or PFC3B examines the IP packets and performs a
route lookup in the FIB TCAM. The lookup result is the pointer to a particular adjacency entry. The
adjacency entry contains the appropriate information for label pushing (for IP to MPLS path) and
encapsulation. The PFC3BXL or PFC3B generates a result containing the imposition label(s) needed to
switch the MPLS packet.
Note If MPLS load sharing is configured, the adjacency may point to a load-balanced path. See
Load Balancing" section on page
OL-4266-08
shows the various functional blocks that support PFC3BXL and PFC3B mode MPLS label
Route
Label updates/
updates/
adjacency
adjacency
IP routing
processes
Route table
process
(RIB)
Label forwarding
table (FIB)
table (LFIB)
Cisco 7600 Series Router Cisco IOS Software Configuration Guide, Release 12.2SX
MPLS
Label bindings
(LIB)
24-8.
PFC3BXL and PFC3B Mode MPLS Label Switching
Control
Data
"Basic MPLS
24-3