Autofs hang processas

Question

I use CentOS 5.5 with Xen. I created RedHat 5.3 DomU and exported some directories through nfs.
In clien side (Dom0) I configured autofs for automatically mounting server's directories.
Server side (DomU):

---

/ets/exports:

/etc            *.rodnower.org(rw,sync,no_root_squash)
/var            *.rodnower.org(rw,sync,no_root_squash)
/administration *.rodnower.org(rw,sync,no_root_squash)

/etc/sysconfig/nfs:

RQUOTAD_PORT=4002
LOCKD_TCPPORT=4003
LOCKD_UDPPORT=4004
MOUNTD_PORT=4005
STATD_PORT=4006
STATD_OUTGOING_PORT=4007

---

Client side (Dom0):

---

/etc/auto.master:

/misc           /etc/auto.misc
/-              /etc/auto.systems
/net    -hosts
+auto.master

/etc/autosystems:

/mnt/dns/administration         -rw,hard,intr   nameserver.rodnower.org:/administration
/mnt/dns/etc                    -rw,hard,intr   nameserver.rodnower.org:/etc
/mnt/dns/var                    -rw,hard,intr   nameserver.rodnower.org:/var

Now, every time I lost connectivity (block all ports with iptables for example) with server, every action in /mnt/dns/* (like ls) will hang the shell.
I tried various combination of soft, hard and intr parameters, but this not change nothing, more of this, even if I mistake in name of parameter (write int instead of intr) there is no any error in any place...

Any one knows what I need to do?

Thank you for ahead.