IPv6 CIDR contains() returns true when it should return false

[natesilva]

Here’s an example:

ip.cidrSubnet('2001:db8:f53b::/48').contains('2001:db8:f53a::1');
// returns: true, should return false

ip.cidrSubnet('2001:db8:f53b::/128').contains('2001:db8:f53a::1');
// returns: true, should return false

This seems obvious so, probably I’m using the library incorrectly, but I can’t see how to fix it.

[willdougadams]

+1

Looks to me like the mask always assumes v4, any mask value over 32 will produce a subnet with numHosts < 1

> for (var i=0; i<128; i++) {
...  console.log('cidr ::1/' + i + '  numHosts: ' + ip.cidrSubnet(`::1/${i}`).numHosts)
...}
cidr ::1/0  numHosts: 4294967294
cidr ::1/1  numHosts: 2147483646

... etc ...

cidr ::1/29  numHosts: 6
cidr ::1/30  numHosts: 2
cidr ::1/31  numHosts: 2
cidr ::1/32  numHosts: 1
cidr ::1/33  numHosts: 0.5
cidr ::1/34  numHosts: 0.25
cidr ::1/35  numHosts: 0.125

... etc ...

cidr ::1/127  numHosts: 2.524354896707238e-29

The tests for the cidrSubnet method here don't test for v6, so it may be that this was intended.

What we can do with v6 is ip.cidr('1111:2222:3333:4444:5555:6666:7777:8888/128') and do some string comparison with the result.

> ip.cidr('1111:2222:3333:4444:5555:6666:7777:8888/128')
'1111:2222:3333:4444:5555:6666:7777:8888'
> ip.cidr('1111:2222:3333:4444:5555:6666:7777:8888/64')
'1111:2222:3333:4444::'
> ip.cidr('1111:2222:3333:4444:5555:6666:7777:8888/32')
'7777:8888::'
> ip.cidr('1111:2222:3333:4444:5555:6666:7777:8888/16')
'7777::'
> ip.cidr('1111:2222:3333:4444:5555:6666:7777:8888/1')
'::'

Would be nice if cidrSubnet() threw an error/warning about this behavior when it detects a v6 address :)

[clarsen]

FWIW, I've found that https://www.npmjs.com/package/subnet-check seems to work for both ipv4 and ipv6 for my purposes.

[natesilva]

That looks like a fork of my package https://www.npmjs.com/package/is-in-subnet — yes, I wrote that specifically for this use case. I’m glad it works for you!