Extreme Networks ExtremeWare Command Reference Manual page 1227

21
ARM Commands
The Accounting and Routing Module (ARM) is a self-contained module for the BlackDiamond switch.
Unlike other BlackDiamond modules, there are no external network interfaces on the ARM. Instead, the
ARM provides advanced IP services for the other input/output (I/O) modules installed in the chassis.
The ARM 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.
The two main features of the ARM are: IP unicast forwarding with selective longest prefix match and
destination-sensitive accounting.
IP unicast packets are routed in the ARM hardware using a longest prefix match algorithim. This differs
from the BlackDiamond's switch fabric, which uses an exact match algorithim. The BlackDiamond's
switch fabric has greater forwarding capacity, but the ARM module has better handling of large
numbers (hundreds of thousands) of IP routes to match each packet's destination IP address. To take
advantage of the BlackDiamond switch fabric's forwarding capacity and the ARM module's scalability,
the ARM module can be configured to use the BlackDiamond switch fabric for some routes, and the
ARM's longest prefix match for others. This feature is called Selective-LPM.
The second feature, destination-sensitive accounting collects statistics that are maintained for forwarded
IP traffic to support billing on a destination basis. To configure destination-sensitive accounting, a bin
number can be assigned to one or more IP route entries using the ExtremeWare command.
route-map
Bin numbers are integers that range from 0-7 and their only intrinsic meaning is to identify a particular
set of accounting statistics. Each bin contains a 64-bit count of the number of packets that have been
forwarded and a 64-bit count of the number of bytes that have been forwarded. When the ARM or
MPLS module forwards an IP packet, the bin number from the forwarding database entry for the IP
destination is used to identify the set of counters to be updated.
Eight unique bins are maintained for each of the possible 4096 VLAN IDs. Logically, the bins are
organized as a two-dimensional array, with the row index being a VLAN ID and the column index
being a bin number. Thus, when an IP frame is forwarded, the input VLAN ID selects the row and the
bin number from the forwarding database entry selects the column. The use of input VLAN ID enables
billing statistics to be maintained on a per customer basis where the VLAN ID identifies the customer.
This chapter documents the ARM command set. Some commands are new for the ARM; other
commands have been enhanced to support the ARM.
ExtremeWare Software 7.0.0 Command Reference Guide 1227