How to connect Ethernet Switch IC with ARM9 CPU
There are three solutions at least: 


Solution 2 (hard) as Xiong describes, a'm only picturing it:


Solution 1 (easy) as Xiong recommends, the picture is:


Solution 0 (ready-to-run): take a SoC with 1xARM9, 1xWAN and 4xLAN switch all embedded:

 

http://www.micrel.com/index.php/products/lan-solutions/arm-based-ethernet-soc.html


I'm surprised seeing this question downvoted because it addresses an architecture very popular even today. And i'm surprised seeing the Xiong's answer downvoted too because except mis-writing "PHY" instead of "SWITCH" (that could be corrected from the context, imo) he was right in full.