Problem is that you need 

dns_lookup_kdc = true

in your /etc/krb5.conf under the [libdefaults] section file:

[root@mysql01 ~]# kinit tom@mds.xyz
kinit: Cannot find KDC for realm "mds.xyz" while getting initial credentials
[root@mysql01 ~]#
[root@mysql01 ~]# vi /etc/krb5.conf
[root@mysql01 ~]# systemctl restart sssd
[root@mysql01 ~]# kinit tom@mds.xyz
Password for tom@mds.xyz:
[root@mysql01 ~]#

Cheers,
TK