Intel IXP1200 3.3 IP-Router Microengine, 3.4 Ethernet Receive Microengine

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

Application Note 23

Modified on: 3/20/02,

3.3 IP-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 A TM Receive micr oengine

rather than on a dedicated IP router microengine.

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.

3.4 Ethernet 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.

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

1. The SDK (Softwa re Development Kit) 2.01 CD contains a number of earlier IXP1200 Ethernet example de sign s that have remained

relatively unchanged from previous releases of the SDK. The Eth ernet receive and transmit code in this example design reuses that code w ith

few modifications