Subordinate CA role transition from 2008R2 to 2012R2

Hi,

I have two PKI. Enterprise CA -2012R2 and SUB CA in 2008R2.

I am going to transition subordinate CA role from 2008R2 to 2012R2.I have only minimal knowledge in Certificate Authority.

Please assist with your answer for my query. if you know the step by step guide for SUB CA transition feel free to share.

Steps:

1. Exporting the Sub CA backup and import into new SUB CA server. After that any modification /changes have to be done for CRL URL
2. Both SUB CA are using different FQDN name. Let me know any changes have to be done after the CA database export.
3. what type of certificates need to exchanged between SUB CA and Enterprise CA
4. Post migration how do I check communication between Enterprise CA and SubCA