RSA Certificate & Key question

Sure. The questions asked were to attempt to understand the challenges. id_rsa keys are not used for TLS traffic, so you would not apply these to BIG-IP SSL profiles. You would normally use this type of key for SSH remote access to some system. You could also see these keys used in an AFM SSH proxy configuration:

• https://support.f5.com/csp/article/K27335364
• https://techdocs.f5.com/en-us/bigip-15-1-0/big-ip-network-firewall-policies-and-implementations/afm-protocol-security/ssh-protocol-security/authenticating-ssh-proxy-traffic/defining-ssh-proxy-password-or-keyboard-interactive-authentication.html

You might have also used id_rsa keys for SSH public key auth to the BIG-IP: https://support.f5.com/csp/article/K13454

Here's some additional information you might find useful regarding TLS certs/keys:

• BIG-IP SSL administration: https://techdocs.f5.com/en-us/bigip-15-1-0/big-ip-system-ssl-administration.html
• Overview of client SSL profiles: https://support.f5.com/csp/article/K14783
• Overview of server SSL profiles: https://support.f5.com/csp/article/K14806
• Managing BIG-IP SSL certificates and keys: https://support.f5.com/csp/article/K17379

Otherwise, AD remote user logon (to the BIG-IP) does not use id_rsa (SSH) keys: https://techdocs.f5.com/en-us/bigip-17-0-0/big-ip-systems-user-account-administration/remote-user-account-management.html

No, don't think so. 

id_rsa and id_rsa.pub are typically how SSH public/private keys are stored. Assuming you're creating client SSL profiles for TLS traffic, those certs are loaded under System ›› Certificate Management : Traffic Certificate Management : SSL Certificate List.

Sorry for misinformation.

I have created profiles, uploaded certificates as well. There are many profiles and for them, I have uploaded total 3 certificate like abc.com, xyz.cn and mno.ru.

When we upgrade the software, we download the keys id_rsa and id_rsa.pub and then upload after upgrade.

I need the clarificatiion what those files contains. As per me, those files contains keys for all three certificate private and public keys. is it true or what os in those two files?

Just cat the files to see what's inside.

cat id_rsa 
cat id_rsa.pub

My guess is you'lll see a single SSH cert and single SSH key, which is not what you're looking for. These are normally key file you'd use to SSH remote into a machine.

The TLS certificates you import for client SSL profiles are generally stored in the file system and will have a .crt or .cer extension.