Understanding Mpls Services - Cisco 3845 - Security Bundle Router Software Manual

Understanding MPLS Services

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The switch supports hierarchical virtual private LAN service (H-VPLS) architecture to simulate LAN
services over the MPLS network. The switch supports H-VPLS using IEEE 802.1Q tunneling or Ethernet
over multiprotocol label switching (EoMPLS). For more information, see these software documents:
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Understanding MPLS Services
In conventional Layer 3 forwarding, as a packet travels across the network, each router extracts the
packet-forwarding information from the Layer 3 header and uses this information as a key for a routing
table lookup to determine the packet's next hop. In most cases, the only relevant field in the header is the
destination address field, but in some cases other header fields are also relevant. For this reason, each
router through which the packet passes must analyze the packet header.
With MPLS, the Layer 3 header is analyzed only once and then is mapped into a fixed-length,
unstructured value called a label. Many different headers can map to the same label, as long as those
headers always result in the same choice of next hop. In effect, a label represents a
forwarding-equivalence class (FEC)—that is, a set of packets that can be very different but that are
indistinguishable to the forwarding function.
The initial choice of label can be based exclusively on the contents of the Layer 3 header, or it can be
based on policy, allowing forwarding decisions at subsequent hops to be based on policy. After a label
is chosen, a short label header is put at the front of the Layer 3 packet and carried across the network as
part of the packet. At subsequent hops through each MPLS router in the network, labels are exchanged,
and the router uses MPLS forwarding-table lookups for the label to make forwarding decisions. It is not
necessary to re-analyze the packet header. Because the label is a fixed length and unstructured, the MPLS
forwarding-table lookup process is straightforward and fast.
Cisco ME 3800X and 3600X Switch Software Configuration Guide
34-2
Configuring MPLS VPNs, page 34-7
Understanding MPLS Traffic Engineering and Fast Reroute, page 34-17
Configuring MPLS Traffic Engineering and Fast Reroute, page 34-20
Understanding EoMPLS, page 34-26
Enabling EoMPLS, page 34-30
Support for H-VPLS, page 34-41
Understanding MPLS OAM, page 34-42
Configuring MPLS OAM and IP SLAs MPLS, page 34-45
Monitoring and Maintaining MPLS and EoMPLS, page 34-60
For information about EoMPLS, see
on page 34-60.
For information about configuring EoMPLS, see the
For information about IEEE 802.1Q tunneling, see the
(EVCs)" chapter.
For information about configuring H-VPLS on Cisco 7600 routers, see the "Configuring
Multiprotocol Label Switching on the Optical Services Modules" section in the OSM Configuration
Note, 12.2SX at:
http://www.cisco.com/en/US/docs/routers/7600/install_config/12.2SR_OSM_config/mpls_ps368_
TSD_Products_Module_Configuration_Guide_Chapter.html#wp1423607
Chapter 34 Configuring MPLS, MPLS VPN, MPLS OAM, and EoMPLS
the"Monitoring and Maintaining MPLS and EoMPLS" section
"Enabling EoMPLS" section on page
"Configuring Ethernet Virtual Connections
34-30.
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