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Cisco 7600 Series Router Cisco IOS Software Configuration Guide, Release 12.2SX
OL-4266-08
Chapter 24 Configuring PFC3BXL and PFC3B Mode Multiprotocol Label Switching
PFC3BXL and PFC3B Mode MPLS Label Switching
•
Supported Cisco IOS Features, page 24-5
•
MPLS Guidelines and Restrictions, page 24-7
•
Configuring MPLS, page 24-8
•
MPLS Per-Label Load Balancing, page 24-8
•
MPLS Configuration Examples, page 24-8
Understanding MPLS
MPLS uses label switching to forward packets over various link-level technologies such as
Packet-over-SONET (POS), Frame Relay, ATM, and Ethernet. Labels are assigned to packets based on
groupings or forwarding equivalence classes (FECs). The label is added between the Layer 2 and the
Layer 3 header.
In an MPLS network, the label edge router (LER) performs a label lookup of the incoming label, swaps
the incoming label with an outgoing label, and sends the packet to the next hop at the label switch router
(LSR). Labels are imposed (pushed) on packets only at the ingress edge of the MPLS network and are
removed (popped) at the egress edge. The core network LSRs (provider, or P routers) read the labels,
apply the appropriate services, and forward the packets based on the labels.
Incoming labels are aggregate or nonaggregate. The aggregate label indicates that the arriving MPLS
packet must be switched through an IP lookup to find the next hop and the outgoing interface. The
nonaggregate label indicates that the packet contains the IP next hop information.
Figure 24-1
shows an MPLS network of a service provider that connects two sites of a customer network.
Figure 24-1 MPLS Network
For additional information on MPLS, see this publication:
http://www.cisco.com/en/US/docs/ios/12_2/switch/configuration/guide/xcftagov_ps1835_TSD_Produc
ts_Configuration_Guide_Chapter.html
Understanding PFC3BXL and PFC3B Mode MPLS Label Switching
PFC3BXL or PFC3B mode supports Layer 3 Multiprotocol Label Switching (MPLS) virtual private
networks (VPNs), and Layer 2 Ethernet over MPLS (EoMPLS), with quality of service (QoS) and
security.
CE1
119118
PE1
P1
P2
PE2
CE2
IP
network
MPLS
network
IP
network
MPLS
network
Host A
Host B
Owned by
service provider