Hello every body
here is my problem
we have a 3 DNS servers (powerEdge 4000)1 primary and 2 secondary , to serve about 4000 simultanious access average
but sometimes the clients says that they can not resolv names , sounds like if the 3 servers are insuffisant
on the RAS routers we configured the 3 dns IP thus all clients have the 3 servers
what i think to do is either :

Do some tunning on the DNS servers ( restrict the zone transfert , recurtion .....ext )
setup an LVS cluster which will work as a primary server ( but for this issue i read that LVS for dns is not really recommanded cause DNS is build to do failover and loadbalancing )

i wonder to know ur opinion about he best way to hold this huge number of DNS request .

thnx from the advance .