Peer cert verificaiton error

Sure. Here is my iRule:

when CLIENTSSL_HANDSHAKE
    {
    set my_serial_number [X509::serial_number [SSL::cert 0]]
    if { [matchclass $my_serial_number eq $::RMS_blacklist] }
        {
        log local0. [concat "BLACKLISTED serial: " $my_serial_number]
        reject
        }
    else
        {
        log local0. [concat "DEBUG - serial: " $my_serial_number]
        }
    }

And some additional info:

- RMS_blacklist is an external data group containing integers. It's meant to contain certificate serial numbers.

- This iRule is assigned to one of our virtual servers, which is enabled only on External traffic (if that counts).

How do I know which side our script is running on? I automatically assumed that it would be running on client-side, but now I'm uncertain.

Thanks for your help in advance,

Tote