Converts a list of CIDRs to an encoded file for time efficient lookups on is a given IP address in any of the CIDR blocks. Each CIDR block is on its own line in the input file. The output file is a binary file that can be read by the cidr-encoder program for searching. The lookup time is O(1) for any IP address. However, to achieve this the output file can easily be several GBs if there are a wide range of CIDR blocks across the IPv4 addresses space.
The calculation for how big a file would take is effectively the largest IP - the smallest IP. As the algorithm uses file offsets to determine if an IP is in a list of CIDR blocks, the largest IP is the largest offset in the file. We use the smallest IP to normalize everything to first offset of a file. This is done to reduce the size of the file so the difference between the two is the size of the file.
$ cidr-encoder -h
Usage of cidr-encoder:
-calc
Calculate the size of the encoded file. Reads from STDIN.
-encode
Encode the CIDRs. Reads from STDIN.
-name string
The file base name to use as the ACL file name(e.g test.acl name is test).
-search string
Search for a IP in the CIDRs.-calc, encode, and search are all mutually exclusive but the priority in the event that all are specified are calc then encode then search.