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In a bash script I have an IP address like 192.168.1.15 and a netmask like 255.255.0.0. I now want to calculate the start address of this network, that means using the &-operator on both addresses. In the example, the result would be 192.168.0.0. Does someone have something like this ready? I'm looking for an elegant way to deal with ip addresses from bash
788
To calculate the IP Address Subnet you need to perform a bit-wise AND operation (1+1=1, 1+0 or 0+1 =0, 0+0=0) on the host IP address and subnet mask. The result is the subnet address in which the host is situated.
In simple words, the Number of hosts in any network can be calculated with the formula = 2x– 2, where x is the number of host ID bits in the IP address.
IPv4 addresses are 32 bits made up of four octets of 8 bits each. To calculate the subnet mask, convert an IP address to binary, perform the calculation and then convert back to the IPv4 decimal number representation known as a dotted quad. The same subnetting procedure works for IPv6 addresses.
Use bitwise & (AND) operator:
$ IFS=. read -r i1 i2 i3 i4 <<< "192.168.1.15"
$ IFS=. read -r m1 m2 m3 m4 <<< "255.255.0.0"
$ printf "%d.%d.%d.%d\n" "$((i1 & m1))" "$((i2 & m2))" "$((i3 & m3))" "$((i4 & m4))"
192.168.0.0
Example with another IP and mask:
$ IFS=. read -r i1 i2 i3 i4 <<< "10.0.14.97"
$ IFS=. read -r m1 m2 m3 m4 <<< "255.255.255.248"
$ printf "%d.%d.%d.%d\n" "$((i1 & m1))" "$((i2 & m2))" "$((i3 & m3))" "$((i4 & m4))"
10.0.14.96
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