There are hundreds of such devices not having host-name and their IP
is not static. So SSL certificates may not be possible here???.
SSL client authentication certificates can be issued without a DNS resolvable name or fixed IP addresses. The server does not have to be configured to use DNS to verify them.
As Stephan suggested, standing up your own PKI for this system seems like the right approach. Unless your organization already has their own PKI, this can be as simple* as using OpenSSL to generate your own self-signed certificate, then using that CA certificate to sign all your server and client certificates. You'll have to install the custom CA certificate as a Trusted Root certificate in each of the servers and clients. (If these are part of a closed ecosystem, consider removing any trusted root certificates that the clients don't need.)
You will probably have an inventory of the devices as part of running your organization. Whatever ID is assigned to them, that would probably be appropriate to set in the DN of the certificates. But you certainly don't have to do that either, especially if you don't want to put your internal name on your certificates. Instead, you can pre-generate a large pile of certificates in advance, and hand them out to new clients when they register with you. Then keep track of the certificate ID and the client ID it was issued to, and use that relationship for granting client permissions. This keeps your issuing CA safely offline from the system that registers your clients.
If your organization has a PKI already, consult with them. They should assign an Organizational Unit reserved strictly to your devices. You can then have your server verify the client certificates have the OU valid only for your devices. That way, other groups in your org won't be able to issue certificates to rogue/unknown devices.
Remember, once devices are out in the field they can possibly be stolen, tampered with, and/or disassembled. Don't place any more trust in the client certificates than you need to. Don't allow these same device certificates to grant administrative permissions on the server. And if a device goes missing, invalidate its certificate quickly.
* I apologize for using the word "simple" in conjunction with PKI.