subnet-tools

POSIX-compliant shell scripts for detection, calculation and aggregation of ipv4 and ipv6 subnets.

trim-subnet.sh

Trims an ipv4 or ipv6 address to a given length (expressed in CIDR mask bits) and outputs the resulting subnet.

Examples:

• Input: sh trim-subnet.sh 192.168.4.111/12. Output: 192.160.0.0/12
• Input: sh trim-subnet.sh 2001:4567:1111:56ff::1/42. Output: 2001:4567:1100::/42

aggregate-subnets.sh

Calculates an efficient configuration for subnets given as an input by trimming down each input subnet to its mask bits and removing subnets that are encapsulated inside other subnets on the list. Intended for easier automated creation of firewall rules. Utilizes the above trim-subnet.sh script as a library.

Options:

-f <family>: force processing subnets for specified family (inet for ipv4 or inet6 for ipv6). If not specified, auto-detects families for input subnets and processes each family separately.

Examples:

• Input: sh aggregate-subnets.sh 192.168.1.1/24 192.168.2.2/16 192.169.3.3/8.

Output: 192.0.0.0/8

• Input: sh aggregate-subnets.sh 192.168.1.1/24 192.168.2.2/16 192.169.3.3/16 fd16:1234:5678:ab:1:1:1:1/64 fd16:1234:5678:ab:2:2:2:2/64 fd16:1234:5678:ab::1/128 fd16:1234:5678:cd:9:9:9:9/60.

Output:

192.168.0.0/16
192.169.0.0/16
fd16:1234:5678:c0::/60
fd16:1234:5678:ab::/64

detect-local-subnets.sh

Detects local area ipv4 and ipv6 subnets, regardless of the device it's running on (router or host). Outputs all found local ip addresses and aggregated subnets these addresses belong to. Some heuristics are employed which are likely to work on Linux but for other Unixes, testing is recommended. Tested on Debian-based Linux distributions and on OpenWRT.

Requires the aggregate-subnets.sh and the trim-subnet.sh scripts to process found ip addresses.

Options:

-s: only output aggregated subnets

-f <family>: only check subnets for specified family (inet for ipv4 or inet6 for ipv6)

detect-local-subnets-AIO.sh

Same as above but as a stand-alone script (does not require aggregate-subnets.sh and trim-subnet.sh). Works faster but skips printing found ip's (only prints the aggregated subnets).

Dependencies

• grep, sed, tr and sort.
• All scripts require the ip-regex.sh script which sets regex variables.

The code is POSIX-compliant (tested on ash, dash and bash) and avoids using non-POSIX extensions of the aforementioned utilities. However, only tested with the GNU variants, and only on Linux. Probably should work on other Unixes but may require slight modifications.

Notes

• These scripts do not make any changes to the system they're running on, do not gather any user data and do not send it anywhere. trim-subnet.sh and aggregate-subnets.sh simply take input, do some calculations and report the results back to console. detect-local-subnets.sh and detect-local-subnets-AIO.sh examine the network configuration on the specific machine they're running on (without making any external connections), do some calculation and report the results back to console.
• If you find any bugs or have a suggestion for code improvement, please let me know.
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