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Hardware Routing Engine (HRE)
page -14 OmniSwitch Troubleshooting Guide September 2005
Router MACs
Helps identify candidate traffic for classification. The HRE only operates on traffic that is identified as
requiring layers 3 and 4 classification. Candidate traffic for such classification must be of the type IP or
IPX and must have its layer 2 destination MAC be a router MAC for this switch or be a bridged MAC that
has been marked for layer 3 and 4 classification or be an IP multicast MAC. This feature only manages
router MACs. Bridged MACs are managed by layer 2 source learning and IP multicast MACs are
managed by the IP multicast routing and switching (IPMS) feature. These resources are used to imple-
ment the forwarding features - IP and IPX unicast routing, IP multicast routing and switching, bridging
based on layers 3 and 4 information, and IP firewall.
IP and IPX Unicast Routing
When an IP or IPX packet is addressed to a router MAC on the switch, the HRE attempts to classify the
packet using data in the pseudoCAMs. If a match is found, the packet is updated and forwarded using
information from header cache entry. If not, the packet is routed using one of two default header cache
entries (one each for IP and IPX). These are configured to route the packet to either the IP or IPX soft-
ware process on the Coronado.
IP Multicast Routing and Switching
When an IP multicast packet is received, the HRE attempts to classify the packet using data in the pseudo-
CAMs. If a match is found, the packet is sent to egress processing which uses the information stored in the
header cache entry as well as other Coronado tables updated by the IPMS feature to forward the packet. If
no match is found, the packet is forwarded to the IPMS software process on the Coronado.
Bridging Based on Layer 3 and 4 Information
When an IP packet is addressed to a MAC with an entry in the layer 2 DA pseudo-CAMs that indicates the
treatment for the bridged packet depends on layer 3 and 4 information, the HRE attempts to classify the
packet using data in the pseudo-CAMs. If a match is found, the packet is not modified but is forwarded
using information from the header cache entry. If a match is not found, the packet is forwarded to the QoS
software task.
IP Firewall
The HRE has the capability to match TCP traffic with particular flag bits set. This capability can be
enabled based on the destination MAC of the packet, the destination host IP address of the packet, or the
final matching pseudo-CAM entry for a flow. When this is enabled and the packet has the appropriate flag
bit set, the packet is forwarded normally and a copy is sent to the IP software process on the Coronado.