Subnet info is lost when converting to v4 address.

[momchil-anachkov]

Hi there,

It seems when converting to a v4 from a v6 address the the resulting v4 address does not retain any of the subnet information even when coming from a "v4 in v6" address.

Steps to reproduce:

const a = Address6.fromAddress4('192.168.0.1/24'); // 24 bit mask
console.log(a.address); // ::ffff:192.168.0.1/120
console.log(a.subnet); // '/120'
console.log(a.subnetMask); // 120
console.log(a.is4()); // true
console.log(a.v4); // true

// This is where the funkiness starts

console.log(a.parsedAddress4); // '192.168.0.1' -- no mask
console.log(a.address4.address); // '192.168.0.1' -- no mask
console.log(a.to4().subnet); // '/32'
console.log(a.to4().subnetMask); // 32

I was expecting if the address is a valid v4 address for it to be preserved with the subnet (24), and not get the default (32).
Am I missing something?

Cheers

[asergeyev]

What would imply /24 as the default for you? An address without netmask normally means "host" address, even one that ends in .0 could be a host in a lots of cases.

Quick quest for an example gives me
mx1.calmtug.com has address 40.76.49.0, host in 40.76.0.0/14 network

When operating with different addresses it's best to assume nothing and treat all addresses without netmask as individual hosts, which is an equivalent of /32 subnet

[beaugunderson]

Hmm, I'm not sure if I foresaw that use case, of instantiating from an Address4 with a subnet and then converting back to an Address4… will have to figure out how to work correctly! if I remember correctly `parsedAddress4` should be viewed as internal, though

…

On Thu, Nov 05, 2020 at 5:10 AM, momchil-anachkov ***@***.***> wrote: Hi there, It seems when converting to a v4 from a v6 address the the resulting v4 address does not retain any of the subnet information even when coming from a "v4 in v6" address. Steps to reproduce: const a = Address6.fromAddress4('192.168.0.1/24'); // 24 bit maskconsole.log(a.address); // ::ffff:192.168.0.1/120console.log(a.subnet); // '/120'console.log(a.subnetMask); // 120console.log(a.is4()); // trueconsole.log(a.v4); // true // This is where the funkiness starts console.log(a.parsedAddress4); // '192.168.0.1' -- no maskconsole.log(a.address4.address); // '192.168.0.1' -- no maskconsole.log(a.to4().subnet); // '/32'console.log(a.to4().subnetMask); // 32 I was expecting if the address is a valid v4 address for it to be preserved with the subnet (24), and not get the default (32). Am I missing something? — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#123>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAAPCX2NXIQAEMSN3QY7L23SOKP3PANCNFSM4TLK66DA> .

[momchil-anachkov]

What would imply /24 as the default for you? An address without netmask normally means "host" address, even one that ends in .0 could be a host in a lots of cases.

Quick quest for an example gives me
mx1.calmtug.com has address 40.76.49.0, host in 40.76.0.0/14 network

When operating with different addresses it's best to assume nothing and treat all addresses without netmask as individual hosts, which is an equivalent of /32 subnet

@asergeyev

Nothing implies that. /24 is a pretty poor default. /32 probably should be the default.
That's not at all what the ticket is about. The issue is that you start from an address with specifically /24, and you lose that information.

Please read the code example. 🙂

[momchil-anachkov]

if I remember correctly parsedAddress4 should be viewed as internal,
though

I see. Thanks. I'll keep that in mind.

Hmm, I'm not sure if I foresaw that use case, of instantiating from an
Address4 with a subnet and then converting back to an Address4… will have
to figure out how to work correctly!

That's okay. It's easy-enough to do some math as a consumer and figure things out.

In this case the ipv6 address has a mask of 120 (8 bits off from 128, which is the max),
So the ipv4 address should have a mask 8 bits off from 32, which would end at 24.

It's just some weird behaviour that I noticed, and thought I'd bring it up. 🙂

Thanks for looking into it.
And thanks for the great library!

Cheers 🥂