I am using IPSet to managed tens of thousands of IPv4 CIDR/netmask ranges that then get linked to IPTables rules. This setup is working great, but I would like to get a good, high-level overview count of the IP host addresses IPSet acts on for client reporting purposes.

The IPSet entry formatting is consistently like this:

123.456.0.0/16 timeout 86400

So I can grep on the lines that have timeout to get values to act on the CIDR/netmask ranges that the entry contains.

For example, if I save the IPSet output (via ipset -L -n > ipset-20181228.txt) to a text file named ipset-20181228.txt and then run a combination of grep and wc -l like this:

grep  "timeout" ipset-20181228.txt  | wc -l

I get a count of 39,000+ items which equate to 39,000+ CIDR/netmask ranges. But that is (of course) only counting the CIDR/netmask ranges and not full counts of IP host addresses in that range.

I attempted to use prips (which expands CIDR/netmask values to actual IP addresses in Bash) with grep to cull out only items with CIDR/netmask ranges like this:

grep -oE '(([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])\.){3}([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])\/([0-9]{1,2})' ipset-20181228.txt | awk 'NF { system( "prips " $0)  }' | wc -l

And after a whopping 20 to 30 minutes (!!!) on my 2018 MacBook Air (with the fans kicking in), the count I got was 736,000,000+ which is what I am going for… But 20 to 30 minutes is way too long. I want this to be as scriptable and non-intrusive as possible, and can’t trust a command like that to run on a production server without eating up resources; I mean look at how it behaves on my local 2018 MacBook Air development setup.

Is there any way to just calculate the CIDR/netmask range count based on simply the CIDR/netmask value? I am hoping there is just some command line tool—or option in existing tools I am using—that I am unaware of that can help.

  • Which conversion do you want? Option A. to Option B. to Nmap, traceroute has some features. – Biswapriyo Dec 29 '18 at 7:19
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    @Biswapriyo Neither. Did you even read the question? I am simply asking to get a count of IP addresses based on CIDR/netmask notation. Not convert from one form of range notation to another. – JakeGould Dec 29 '18 at 12:30
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    If I understood correctly, you want to know how many hosts are in a given ip/mask pair. The hosts number is 2^(32-mask)-2. The mask represents the net bits, so the other part represents the hosts bits. -2 is for the net address and broadcast ips. If you have ipcalc installed run it to see those information. (Excuse-me if I misunderstood your question). – Paulo Dec 29 '18 at 12:57
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    @Paulo: Do not subtract 2; do not assume that each range directly corresponds to a subnet. Routes and filter lists have no correspondence to physical layout – an entry might match just part of a subnet, or cover multiple subnets at once, or even apply to networks which have no concept of "subnet" in the first place (e.g. point-to-point links). And really, whether an address represents a host or not isn't even relevant in filtering. Each prefix has exactly 2^(32-mask) addresses and that's it. – grawity Dec 29 '18 at 15:58
  • @grawity I see your point, I think I was stuck to the concept of a subnet range. That range from the question can be a range of ips, just like you said. Thanks for clarifying. I subscribe to 2^(32-mask). – Paulo Dec 29 '18 at 18:21

If your grep command outputs lines like 123.456.0.0/16, then you need to pipe them to

awk -F / '{ count[$2]++ } END { for (mask in count) total+=count[mask]*2^(32-mask); print total }'

The command only extracts masks (i.e. what is after /) and counts occurrences of each mask. At the end the number of hosts is calculated for each encountered mask (2^(32-mask)), multiplied by the number of occurrences and summed up.


  • No sanity check is performed. E.g. input like will be accepted, non-integer output will be calculated. Improve your preliminary grep filter if needed.
  • Each range independently contributes to the total number. If your ranges overlap then you will get an inflated result (I think your try with prips was no better in this).
  • This is excellent. Running it as follows works quite quickly and the final command I used this with is: grep -oE '(([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])\.){3}([0-9]|[1-9][0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])\/([0-9]{1,2})' ipset-*.txt | awk -F / '{ count[$2]++ } END { for (mask in count) total+=count[mask]*2^(32-mask); print total }' – JakeGould Dec 30 '18 at 0:07

I thought something like this would work since the original poster is running grep to get the CIDR from lines with timeout:

awk -F'[ /]' '/timeout/ {hosts+=2^(32-$2)};ENDFILE{print "Hosts number in "FILENAME": "hosts;total+=hosts;hosts=0};END {print "Total: "total}' ipset*.txt

EDIT- The awk program above runs ok only with GNU awk. ENDFILE is a GNU extension.

I guess BSD awk ignores ENDFILE and runs that section if it was part of the main program section.

This is compatible with GNU and BSD awk.

awk -F'[ /]' '{if (filename != FILENAME) hosts=0};/timeout/ {hosts+=2^(32-$2)};{filename=FILENAME;file_total[filename]=hosts};END{for (i in file_total) {print "Hosts number in "i": "file_total[i];total+=file_total[i]};{print "Total: "total};}' ipset*.txt
  • Your revised script works in macOS, but as I explained previously it’s horribly over counting in macOS now as well as Linux: I am getting a hosts number of 8,500,000,000,000+ using your script instead of the expected 736,000,000+ I am using in a live sample test file with the accepted answer as well as prips. Sorry, thanks for the effort but this is not working to say the least. – JakeGould Dec 30 '18 at 4:33
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    @jakegould Ok, not a problem at all. Probably I didn't understand the output to filter it correctly. Besides I couldn't get an easy way to install prips and take a look how it works and it's output. Anyway it worth the exercise to get the awk report without any GNU extension. – Paulo Dec 30 '18 at 4:39

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