IP-Router Microengine, Ethernet Receive Microengine

IXP1200 Network Processor Family ATM OC-3/12/Ethernet IP Router Example Design

3.3IP-Router Microengine

The IP Router microengine consumes packets from the ATM receive microengine via a message queue, and routes them to the appropriate Ethernet transmit packetq. In the IXP1200 software-CRC configuration, this function is carried out by two threads residing on the ATM Receive microengine rather than on a dedicated IP router microengine.

3.3.1Structure

All threads are identical. In hardware-CRC configurations, four IP Router threads reside on the dedicated IP-router microengine. In the software-CRC configuration, two IP Router threads reside on the ATM Receive microengine.

3.3.2High Level Algorithm

Figure 14. IP Router High Level Algorithm

while(1)

msgq_receive() packet from ATM RX engine ip_filter() out SNMP, IGMP

ip_addr_validation() to discard packets from reserved addresses

ip_dbcast_check() to filter out packets from directed broadcast addresses ip_proc()

ip_verify() check TTL and checksum ip_modify() update TTL

ip_route_lookup()

port_enabled_check() to discard packets from disabled port update Ethernet MAC Source Address with our own

#ifdef ATM_LOOPBACK //Allow hardware configurations with ATM outputs //connected directly to ATM inputs

if(output port == ATM port)

over-ride ATM destination port with round-robin Ethernet port

#endif

packetq_send() packet to destination Ethernet port

3.4Ethernet Receive Microengine

The Ethernet Receive microengine is based on rx_ether100m.uc, an extended version of the Ethernet receive threads from the Software Development Kit’s (SDK's) 16-port Ethernet example design1. While the code looks quite different from that on the SDK, most of the changes required a simple move to a more efficient structure, without changing the logical function of the microengine. For example, the threads take advantage of updated APIs for the RFC1812 macros to lower the overhead of RFC1812 support.

Semantically, there are only a few differences from the SDK Ethernet design.

•IP lookup can return an ATM destination port, or an Ethernet destination port.

•For ATM destinations, prepend the LLC/SNAP to the payload.

•For ATM destinations, append the AAL5 trailer.

1.The SDK (Software Development Kit) 2.01 CD contains a number of earlier IXP1200 Ethernet example designs that have remained relatively unchanged from previous releases of the SDK. The Ethernet receive and transmit code in this example design reuses that code with few modifications

Application Note

Modified on: 3/20/02,