hi all,
i want to check the security of DNS server on our LAN which is connected to internet ,but i have no knowlege about this issue,whould some one explain what are the common attacks on DNS servers and what are the preventation actions against them ?
i have seen some information about creating chroot jail for increasing the security .

This is a huge topic. But basically, make sure that you're running an up to date version of BIND with all security fices enabled. Also make sure that only DNS slaves are allowed to do zone transfers (if it's a master server for any zones). Consider setting up RNDC (I think's that's the name...) for secure zone transfers and to prevent malicious people from trying to spoof your slave. DNS security is a huge field, encompassing stuff like this plus cache poisioning etc. Chrooting only helps a bit by limiting damage to the DNS server if there is a break in, but there's lots more that can go on. I would suggest doing a Web search on the topic for more details.

Of course, you need to follow general best practices for host security too (i.e. if root's password is toor, then you have a problem).