Blocking IPs

[Dan]

I'm building a list of IP ranges (currently CIDRs) and want to use  
them to:

1) Tag/block messages that arrive (directly and indirectly) from IPs  
in these ranges

2) Tag/block messages with URIs that point to IPs in these ranges


What is the best way to define specific/fixed IP ranges for  
blocking?  Can the URI lookup system be configured to check A-record  
IPs against these lists or if needed, separately defined IP range lists?

Thanks,
Dan