Extreme Networks ExtremeWare 7.3.0, Справочник по командам

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ExtremeWare Software 7.3.0 Command Reference Guide 1751
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MPLS Commands
The MultiProtocol Label Switching (MPLS) module is a self-contained module for the BlackDiamond
switch. Unlike other BlackDiamond modules, there are no external network interfaces on the MPLS
module. Instead, the MPLS module provides advanced IP services for the other input/output (I/O)
modules installed in the chassis. The MPLS module contains a powerful set of packet processing
resources that operate in a one-armed fashion: receiving frames from the switch fabric, processing the
frames, and transmitting the frames back into the switch fabric.
MPLS encompasses a growing set of protocols defined by the IETF. True to its name, MPLS is based on
a label-switching forwarding algorithm. ATM and Frame Relay are examples of other protocols that use
label-switching forwarding algorithms.
Conceptually, label switching is straightforward. A label is a relatively short, fixed-length identifier that
is used to forward packets received from a given link. The label value is locally significant to a
particular link and is assigned by the receiving entity.
Because labels are relatively short (for example, 20 bits in a MPLS shim header), the label of a received
packet can be used as an index into a linear array containing the forwarding database. Forwarding
database entries indicate the outgoing port and any label(s) to be applied to forwarded frames. Thus,
forwarding may consist of a simple lookup and replacement of the incoming label with the appropriate
outgoing label (otherwise known as
label swapping ).
The MPLS module includes the following features:
• MultiProtocol label switching (MPLS) —MultiProtocol Label Switching (MPLS) is a forwarding
algorithm that uses short, fixed-length labels to make next-hop forwarding decisions for each packet
in a stream.
• IP unicast forwarding (longest prefix match) —IP unicast packets are forwarded in the hardware
using the longest prefix match algorithm. IP unicast forwarding is required to switch packets at
ingress or upon egressing an MPLS network domain.
• Destination-sensitive accounting —Counts of IP packets and bytes are maintained based on the IP
routes used to forward packets. Destination-sensitive accounting gives you the flexibility to bill your
customers at predetermined and different rates. The rates are based on the customers’ IP unicast
packet destinations.
The accounting feature categorizes IP unicast packets using two parameters, input VLAN ID and
accounting bin number. The VLAN ID is used to identify from which customer the packet is
received. The accounting bin number is associated with the route used to forward the packet.
External billing application servers can correlate the accounting bin number to a specific billing rate.