Re: [pve-devel] [RFC PATCH pve-installer 6/6] closes #5757: common: add checks for valid IPv4 address within subnet

From: "Christoph Heiss" <c.heiss@proxmox.com>
To: "Michael Köppl" <m.koeppl@proxmox.com>
Cc: Proxmox VE development discussion <pve-devel@lists.proxmox.com>
Subject: Re: [pve-devel] [RFC PATCH pve-installer 6/6] closes #5757: common: add checks for valid IPv4 address within subnet
Date: Mon, 28 Apr 2025 12:22:24 +0200	[thread overview]
Message-ID: <D9I74CTEHVFV.POZJ09D616IN@proxmox.com> (raw)
In-Reply-To: <20250422162739.255641-7-m.koeppl@proxmox.com>

On Tue Apr 22, 2025 at 6:27 PM CEST, Michael Köppl wrote:
> Implement check if the address entered by the user is valid within the
> given subnet, i.e. not a network address or broadcast address.
>
> Partially closes [0].
>
> [0] https://bugzilla.proxmox.com/show_bug.cgi?id=5757
>
> Signed-off-by: Michael Köppl <m.koeppl@proxmox.com>
> ---
> Some input / discussion would be much appreciated here, since this might
> again be considered too restrictive. Multiple questions came up during
> in-person discussion:
> * Is check for broadcast address desired or is it considered a valid
> configuration for PVE?

At least for IPv4 /31 prefixes, this check (including the network
address part) is wrong. RFC 3021 [0] explicitly allows such subnets for
point-to-point links.

E.g. 192.168.0.0/31 is a valid subnet with 2 hosts, 192.168.0.0/31 and
192.168.0.1/31.

[0] https://www.rfc-editor.org/rfc/rfc3021

> * Is IPv6 check necessary and if so, is allowing to set the address to a
> broadcast address a valid setting for IPv6?

There's no traditional broadcast in IPv6, so no check necessary.
(FWIW, multicast takes that role basically)

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