Convert ip ranges to CIDR netblocks Post: 303015047

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Top Forums Shell Programming and Scripting Convert ip ranges to CIDR netblocks Post 303015047 by Chubler_XL on Monday 26th of March 2018 10:30:35 PM

03-26-2018

Moderator

Quote:

Originally Posted by rgopichand

Hi, I have list of IP's ~3k, which are from very small to large subnets. So, I want the IPs to be grouped into subnets that makes sense. The scenario is several groups get IP's based on availability and none of the group should not touch or scan the other IP's. We get the list of IPs based on manual inventory from each group and the key to this part is the provider doesn't manage which set of IPs belong to which group.
So the task is I collected manually all the IPs (which are around 3K) and want to make them into subnets to the nearest class. For example if I have a single IP address it should round off to /32 or if it has 4 ip's it should round off to /29 or /30. I have CIDR tools to do this task, but it needs manual input each time.

I'm looking for a way if I put the 3K ip's into excel or any format the script should round off to nearest subnet class.

You could try sorting the IPs in ascending order and continue to add IPs to the subnet until the standard deviation exceeds a limit and rule the subnet of at that point.

Below I've chosen limit at 200, you can play with different values and see how the grouping comes out (somewhere between 100 and 3000 seems fairly good).

Note: just the starting and ending IPs are output for each subnet found, it wouldn't be too complex to determine the closest mask that covers both of these, if needed.

Code:

@include "lib_netaddr.awk"

function sanitize(ip) {
    split(ip, slice, ".")
    return slice[1]/1 "." slice[2]/1 "." slice[3]/1 "." slice[4]/1
}

function grpstd(val, tot, cnt, mean, sqtot) {
    for(val in grp) {
       tot=tot + grp[val]
       cnt++
    }
    mean = tot / cnt
    for(val in grp) {
       sqtot = sqtot + (grp[val] - mean) * (grp[val] - mean)
    }
    return sqrt(sqtot / cnt)
}

BEGIN { limit=200 }

{ k[NR]=ip2dec(sanitize($1)) }

END {
    n=asort(k)

    for(idx=1; idx <= n ; idx++) {
       grp[++have]=k[idx]
       if(grpstd() > limit) {
          print "Subnet from " dec2ip(grp[1]) " to " dec2ip(grp[have-1])
          have=split(grp[have], grp)
       }
    }
    if (have)
          print "Subnet from " dec2ip(grp[1]) " to " dec2ip(grp[have])
}

Also note I'm not a statistician and there are probably much more efficient ways this sort of thing could be achieved.

Last edited by Chubler_XL; 03-27-2018 at 12:16 AM.. Reason: Calculation error in standard deviation function - updated default limit value

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