i have small doubt on domain-tag X value.
where to use domain-tag and what should be domain-tag value.
It should be same as autonomous number or it can be any value.
It's used to prevent loops in MPLS Core when OSPF is used as a PE-CE routing protocol.
When BGP routes are redistributed into OSPF at PE; Lowest 16-bits of domain-tag are set to same value as of AS number by default. If another PE recieves the routes with same tag that is has set; will ignore those LSA's. Therefore it prevents the redistributed routes to re-enter MPLS Core.
It's not mandatory that it should match AS number. You can specify domain-tag of your own choice.