Inside The Provision Asic Architecture; Classification And Lookup; Policy Enforcement Engine; Network Switch Engine Programmability - HP ProCurve 3500-24 Reference Manual

Figure 1 illustrates an example of the logical interconnection of the ProVision ASICs on the 6-slot Switch 5406zl .
All of the key elements are connected to the active backplane . The active backplane contains the switch fabric
and distributes power to all modules . The HP ProCurve Switch 5400zl, 3500, and 6200yl series have similar
architectural components . The primary difference in the illustration would be the number of ports supported .
The Switch 8200zl series offers a comparable architecture with modular switch fabric and redundant switch
management modules .

Inside the ProVision ASIC architecture

Each line interface module contains a full ASIC-based Layer 3 routing switch engine as well as Layer 4 filtering
and metering . These new ProVision ASICs are HP ProCurve's 4th-generation switching ASICs . This network
switch engine, in the ProVision ASICs, provides all the packet processing: Layer 2 and Layer 3 lookups; filtering
and forwarding decisions; and VLAN, trunking, and priority queuing determinations . The ProVision ASIC on
each line card contains its own CPU . These features of the ProVision ASIC are common for all products in the
HP ProCurve Switch 3500, 5400zl, 6200yl, and 8200zl series .

Classification and lookup

When a packet first comes in, the classifier section determines the packet characteristics, its addresses, VLAN
affiliation, any priority specification, etc . The packet is stored in input memory; lookups into the table memory
are done to determine routing information; and a ProVision ASIC-specific packet header is created for the
packet with this information . This header is then forwarded to the Policy Enforcement Engine .

Policy Enforcement Engine

The ProVision ASICs on each line interface module contain the Policy Enforcement Engine . This engine provides
fast packet classification to be applied to ACLs, QoS, Rate Limiting, and some other features through an
onboard Ternary Content Addressable Memory (TCAM) . Some of the variables that can be used include source
and destination IP addresses (can follow specific users), TCP/UDP port numbers, and ranges (apply ACLs to
an application that uses fixed port numbers or ranges) . Over 14 different variables can be used to specify the
packets to which ACL and QoS rules, rate limiting counters, and others are to be applied .
Partially implemented in the initial software release, the Policy Enforcement Engine will provide a common front
end for the user interface to ACLs, QoS, rate limiting, and some other services . In subsequent software releases
for the switches, more features can take advantage of the Policy Enforcement Engine to provide a powerful,
flexible method for controlling the network environment . For example, traffic from a specific application can be
raised in priority for some users, blocked for some other users, and limited in bandwidth for yet other users .
After going to the Policy Enforcement Engine, the header is then forwarded to the programmable section of the
network switch engine .

Network switch engine programmability

Each ProVision ASIC switch engine contains multiple programmable units, making them truly Network
Processor Units (NPUs) . One of the functions of the NPU is to analyze the header of each packet as it comes
into the switch . The packet's addresses can be read with the switch making forwarding decisions based on
this analysis . For example, if a packet's 802 . 1 Q tag needs to be changed to re-map the packet priority, the
ProVision ASIC needs to look at each packet to see if any particular one needs to be changed . This packet-by-
packet processing has to occur very quickly to maintain overall wire-speed performance—a capability of the
ProVision ASICs .
To broaden the flexibility of the ProVision ASICs, a programmable function is included for its packet processing .
This NPU function allows the HP ProCurve designers the opportunity to make some future changes or additions
in the packet processing features of the ASIC by downloading new software to it . Thus, new features needing
high-performance ASIC processing can be accommodated, extending the useful life of the switch without the
need to upgrade or replace the hardware .
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