Clean-installation of Leopard having issues with OD but upgrading not

Question

The server is a 10.4.11 with open directory, dns and AFP that it was working fine with 20 iMac (10.4.11) for long time, we are considering to update the clients to Leopard, the big problem is coming to connect with the OD, if I upgraded a tiger imac to leopard it works perfectly taking 10 seconds to connect. But if I do a clean installation it takes 10-20 min or sometimes doesn't connect. Curiously if I try to add the OD in the Directory Utility using the name it takes 5 mins but using the IP is immediately. Please, ready what I check before to tell me that it is a dns problem.
-- I've checked all the network settings, /etc/resolv.conf, /etc/hosts , etc being the same that the client upgrated from tiger that works fine.
-- I've checked all settings in the Directory Utility.
-- The client is up-to-date with the server
-- The file /Library/Preferences/edu.mit.Kerberos is right.
-- nslookup,ping and trace work fine and with good timing.
-- I've stopped the OD server (setting standalone and starting again), without any help.
-- Physical connection obviously is ok
Any help could be valuable, thanks in advance

Answer 1

first at all thanks for your help.
All the clients have in the primary dns the server ip, and the server doesn't have dhcp server because all the machines use fixed ip. Btw I'm using the same settings that the tiger clients, and these always work perfectly..
the result of the changeip is:
[server.ds.perico] /Users/macroot > sudo changeip -checkhostname
Password:
Primary address = 192.168.7.20
Current HostName = server.ds.perico
DNS HostName = server.ds.perico
The names match. There is nothing to change.
Thanks in advance