router question

I have two ethernet cards in my SuSE 7.3 system and can't get packets to forward between them. I have IP_FORWARD="yes" in my rc.config file. Is anything else necessary? -- inet: john@wilkes.com | addr: 321 High School Rd. NE #367 | "The man who views the world at 50 the city: Bainbridge Island, Washington | same as he did at 20 has wasted 30 code: 98110-1697 | years of his life." icbm: 47 37 48 N / 122 29 52 W | - Muhammad Ali