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Hardware Routing Engine (HRE)
OmniSwitch Troubleshooting Guide September 2005 page -13
Hardware Routing Engine (HRE)
This feature is responsible for managing the Coronado HRE resources that perform IP and IPX packet
classification and forwarding.
This functionality employees five principal Coronado resources—header cache entries, pseudo-CAM
entries, hash function registers, modes, and router MACs.
Header Cache Entries
Contain the information necessary to modify and forward a packet, including both modifications to the
packet’s content and Coronado-specific handling information.
Pseudo-CAM Entries
Used for classifying traffic based on its IP or IPX address information and, in the case of IPMS, some
layer 2 information. The HRE does not have Content Addressable Memory (CAMs) for storing address
information. Instead it uses hash tables (called pseudo-CAMs) that can be interpreted by the Coronado.
The entries in these hash tables contain both address information to be matched against the content of the
packet and the resulting action to take when the entry is matched. There are two basic actions:
• Forward the packet using information in a specified header cache entry.
• Perform another refining lookup to match additional, more specific address information.
Hash Function Registers
Used to define the hash algorithms used to lookup pseudo- CAM entries in the hash tables.
Modes are used to govern the classification process:
Mode 0 For IP entries, full IP destination host address. For IPX, destination
network number.
Mode 1 For IP entries, full IP destination and source host addresses. For IPX,
not used.
Mode 2 For IP entries, full IP destination and source host addresses and TCP/
UDP destination port number. For IPX, IPX destination network
number and IPX destination node.
Mode 3 For IP entries, full IP destination and source host addresses and TCP/
UDP destination and source ports. For IPX, not used.
Mode 4 Only used for IP firewalling. Uses same matching criteria as Mode 3.
Mode 5 Only used for IPMS. Matches full IP destination and source host
addresses, source port number, and source VLAN identifier.
Mode 6 Unused.
They identify which hash table is to be used, which hash function is to be used, and what portions of the
address information in the packet are required to match that in the pseudo-CAM entry. There are seven
modes, each represented by a configuration register. Some of these have special meaning. For example,
mode 0 is the initial mode. Each packet classification starts in this mode. Each pseudo-CAM entry that has
as its action to perform another lookup includes a number representing the mode to be used in that subse-
quent lookup.