[nycbug-talk] CIDR Network Subtraction Tool?

[Tim A.]

Scenario:
spamd blacklisting from foreign.txt source file with a list of all 
non-US IP space.
Problem:
Occasionally we spark up a new non-US vendor relationship and need to 
receive email from their email servers but their IP addresses have been 
blacklisted in foreign.txt
Solution:
Subtract their IPs / ISPs netblock from the /8 entry.
Currently, I do this by hand. Googling for network calculators spits 
back a ton of tools that calculate subnets but none of which do this 
sort of network subtraction.
If anyone is aware of such a tool, please share.

Example:
       89 .  0 .  0 .  0   /8
-      89 .208 .106 .  0   /24
-------------------------------



89.0.0.0/9
89.128.0.0/10
89.192.0.0/12
89.208.0.0/18
89.208.128.0/18
89.208.192.0/18
89.208.64.0/19
89.208.96.0/21
89.208.104.0/24
89.208.105.0/24
89.208.107.0/24
89.208.108.0/24
89.208.109.0/24
89.208.110.0/24
89.208.111.0/24
89.208.112.0/20
89.224.0.0/11


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