I think is the gateway setting cause the problem. Many users were facing the same problem since upgrade to 10.2

I think that's right. I've had this issue with multiple Slack boxes being upgraded from 10.1 to 10.2. Good to know a way around it though

Even after I make a new installation, the problem was same too.

I've found that Slackware is the installation that you really have to make notes about how you did things so when you install somewhere else you can remember what you've done. I remember on the 10.1 that mySQL would never load right. I eventually made a check list of things I needed to do to get it running. I installed it the same way on 4 machines. All had the problem. So either I messed up 4 times the same way or there was some sort of issue with the way I was doing it or how it was compiled. (I'd guess I was the problem first, but who knows. )

Slackware, gotta love it!