Utility script to show unused gaps in IP space within a list of networks.
This script was born out of a need to find unused subnet space within a large, micro-segmented VPC in AWS. Sorting the subnets and looking for spaces manually isn't easy on the eyes. The first iteration of this script used a file input which was accomplished by copying and pasting subnets out of the AWS UI and then massaging the data to remove the extra information. Once I proved that the logic worked, I added the functionality necessary to get the subnet information straight from the source. I hope you find it useful.
The script takes either the filename or the vpcid argument... not both.
usage: subnet_gap_finder.py [-h] [--filename FILENAME] [--loglevel LOGLEVEL]
[--vpcid VPC_ID]
Utility script to show unused gaps in IP space within a list of networks.
optional arguments:
-h, --help show this help message and exit
--filename FILENAME, -f FILENAME
Path to a file containing a list of IP networks.
EITHER "filename" OR "vpcid" IS REQUIRED
--loglevel LOGLEVEL, -l LOGLEVEL
Specify log level as text string: ERROR, WARNING,
INFO, DEBUG
--vpcid VPC_ID, -i VPC_ID
ID of a VPC in AWS to query. Subnets will be checked
as the list of networks. EITHER "filename" OR "vpcid"
IS REQUIRED.
File input expects a newline-separated list of subnets in the file. Any line containing other text is thrown out, so you don't need to clean up your data too much.
$ python3 subnet_gap_finder.py --filename tests/example.txt
| Gap Start | Gap End | Gap CIDRs |
|-------------+------------+---------------|
| 10.0.6.128 | 10.0.6.255 | 10.0.6.128/25 |
| 10.0.7.32 | 10.0.7.63 | 10.0.7.32/27 |
| 10.0.7.128 | 10.0.7.159 | 10.0.7.128/27 |
VPC mode basically works the same way, with the exception that we can also see unused space at the end of the last subnet until the end of the VPC address space. This is (currently) only shown if there aren't any gaps between subnets.
NOTE: We're not handling AWS authentication in the script. Ensure that you authenticate via the AWS CLI prior to running.
$ python3 subnet_gap_finder.py --vpcid vpc-a675b09
| Gap Start | Gap End | Gap CIDRs |
|-------------+-------------+---------------|
| 10.0.8.0 | 10.0.15.255 | 10.0.8.0/21 |