16-28
ATM Switch Router Software Configuration Guide
OL-7396-01
Chapter16 Configuring Tag Switching and MPLS
Configuring Label Edge Routing
Figure 16-7 shows a packet as it traverse a network from its source on network 130.0.0.0 to its
destination on network 180.0.0.0.
Figure16-7 ATM MPLS Example Network Packet Transmission
The packet from network 130.0.0.0 enters router AdminRt1 at Ethernet interface 2/3 wi th a destination
IP address on network 180.0.0.0. The router preforms a standard routing table lookup and determines
the packet should be routed out ATM interface 0/0 to the next hop interface 140.0.0.1 on interface ATM
1/0/0. By using CEF (Cisco Express Forwarding) the Layer 3 switched packet interface FIB (forwarding
information base) is queried and the next hop is determined to be out through ATM MPLS interface
3/0/0. Prior to transmission to the next LSR an MPLS label (or VPI/VCI) is appended to the packet just
before the destination IP address.
From this point on through the MPLS network, the only informat ion that is checked by the successive
LSRs is the label information in the packet. When the packet reaches the edge LSR the MPLS label is
popped off and subsequent switching is completed using Layer 3 and standard routing practices.
Configuring Label Edge Routing
This section describes label edge router (LER) for the Cisco Catalyst 8540. With LER, the Cisco Catalyst
8540 can be installed at the edge of a packet- and cell-based network with both or either of them
MPLS-enabled. LER also supports multiple TVCs to the same destination prefix and allows a TVC to
130.0.0.0
140.0.0.0
150.0.0.0
160.0.0.0
170.0.0.0
180.0.0.0
e2/3 a0/0
e0/3 a1/0 a1/1/0
a1/2/0
a3/0/0
a3/0/0
a1/0/0
a9/0/0
.1 .1
.1
.1
.2
.2
.2
.2.1 .1
68271
SalesRT1
Loopback 5.5.5.5
Routing
table
AdminLSR1
Loopback 2.2.2.2
SalesSR3
Loopback 4.4.4.4
NetLSR2
Loopback 3.3.3.3
AdminRt1
Loopback 1.1.1.1
FIB
table
LFIB
table
Routing
table
FIB
table
LFIB
table
= Packet
= Packet with VPI/VCI label