Issuing CA installation

Hi All,

I have basic question on Subordinate CA installation.

I have a 2 tier hierarchy for PKI in my test lab. As per the procedure, after the subca is installed, the .req file will need to be carried to rootca server. ROOTCA server will issue the certificate. we will export the certificate and install it in SUBCA.

However my question is, when we are exporting the certificate from rootca, we will export it in .cer or .p7b format and why not other format.?