I've purchased a Cisco ASA5510. I currently have 3 of the 4 licensed interfaces being used. My third port on the ASA is configured as the internal interface. I would like to have the 4th port set up to be an internal interface too. This would allow me to connect two devices that live inside the internal network and it prevents me from purchasing an additional switch. The PIX 501's did this by default, will the ASA5510 allow me to do this?
No, the ASA will not allow you to do this in a way the Pix501 did. The 4 ports on the Pix501 are a built-in switch, the 4 ports on the ASA are real configurable interfaces.
You can configure the 4th interface for a new internal network, but this network has to be different from the internal network you already have.
You are probably better off buying a small switch instead, it will probably cost more man-hours than it will cost you a small switch!
Please rate if the post helps!