Is it possible to query against the ldap server stored in drupal without reconnecting?
So I assume that you are using the LDAP module?

I've not looked into the code they use however I would expect that they will close the connection before your module runs, and even if they don't the connection won't be a global variable so your module will not have access to it.

If you are writing a custom module then you do have access to the DB - just use db_query and fetch the results, or look in your settings file for your connection details. Then you can connect directly to your DB using software like Navicat.

The table ldap_servers has a field called address. This is where you will find the address to your ldap server.