NIS Slave doesn't work while master goes done??

[Cray]

I have setup ready two servers as:

[server 1] NIS Master, NIS Client
[server 2] NIS Slave, NIS Client

When server 1 is down (nis server stop), server 2 will not work as expected to query NIS service to Slave (server2).

What can I do??
----------------------------------------
server1# /sbin/init.d/nis.server stop
...
server2# ypwhich
Domain DEP not bound on server2
server2# domainname
DEP
server2# ypcat hosts.byname
ypcat: can't bind to an NIS server for domain DEP.
Reason: can't bind to a server that serves NIS domain
-------------------------------
NIS client setting on server2:
-------------------------------
server2# ypinit -c
...
next host to add: server2
next host to add: server1
...

server2# cat /etc/rc.config.d/namesvrs
...
NIS_MASTER_SERVER=0
NIS_SLAVE_SERVER=1
NIS_CLIENT=1
NIS_DOMAIN=DEP
MAX_NISCHECKS=2
YPSERV_OPTIONS=""
YPBIND_OPTIONS=""
YPPASSWDD_OPTIONS="/etc/passwd -m passwd PWFILE=/etc/passwd"
KEYSERV_OPTIONS=""
YPUPDATED_OPTIONS=""
YPXFRD_OPTIONS=""
YPSET_ADDR=""
...

[Cray]

server2# cat /var/yp/binding/DEP/ypservers
server2
server1