ppp -ddial my_lable twice brings tun0 and tun1, how to close one?

I'm learn how to use ppp to connect to Internet,
I tried the command twice, and got tun0 and tun1,
but find no way to close them?
You shouldn't worry about tun1 existence as long as interface isn't UP (i.e. you have killed ppp using that interface). If you really don't want to see tun1 in ifconfig output, try `ifconfig tun1 destroy`.