Hello everybody!

I have six NW servers in one tree. Four servers of NW 5.1 SP7 + Edir and two servers of NW 6.5 SP7 + Edir 8.8 SP2. About 1000 Novell Clients starting from 4.83 SP3 till 4.91 SP4
Master replica of the tree is on NW 5.1 SP7 server.

I want clients to allow to log into the network even if only 1 NW server is alive.
What is the best practice to achieve this?