samba - Aug 2013 - Additional domain controller - not answering the authentication request

Hello,

I have successfully installed samba4 with bind as active directory
controller which is working perfectly fine.

I followed
https://wiki.samba.org/index.php/Samba4/HOWTO/Join_a_domain_as_a_DC and
setup another server for  additional domain controller which is installed
successfully.

Replication from DC1 to DC2 working fine... i can see all users in DC2
within few mins.

But the problem is:

When DC1 is down; users are not able to login into system; they get error
message as "no logon server available". It look like DC2 is not able
to
authenticate the users.

On DC1 if i run:
# host your.zone.com

I get following output

your.zone.com has address 192.168.0.1

but expected output should be:

your.zone.com has address 192.168.0.1
your.zone.com has address 192.168.0.2


Can someone help me on this?

ITSAHEB