Invidual DHCP static host gateway override "none" fails

[TheLinuxGuy]

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Describe the bug

A DHCPv4 service on an interface allows setting 'gateway=none' globally. When creating a static DHCP assignment for a single host/ip/mac, under gateway overrides for that host 'gateway=none' throws an error.

This is seen as unexpected, I should be able to override this one host's gateway setting that may be global. "none" works when set at interface level - therefore an override should be possible at host level.

Tip: to validate your setup was working with the previous version, use opnsense-revert (https://docs.opnsense.org/manual/opnsense_tools.html#opnsense-revert)

To Reproduce

OPNsense 21.1.3-amd64FreeBSD 12.1-RELEASE-p14-HBSDOpenSSL 1.1.1j 16 Feb 2021

Steps to reproduce the behavior:

1. Go to Services > DHCPv4 > LAN
2. Click on / add a "DHCP Static Mappings " for a single host mac and IP pair.
3. On the newly created entry, override gateway with "none" value
4. See error

The following input errors were detected:

A valid IP address must be specified for the gateway.
The gateway address none does not lie within the chosen interface's subnet.

Expected behavior

Override "none" for gateway address should NOT fail in the individual static mapping page. It does work fine on the parent interface global setting "none"

Describe alternatives you considered

There isn't any other than manual overriding at client level. We want the DHCP server to respond to DHCP DISCOVER with the override values for the mac address. It's broken.

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Additional context

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Environment

OPNsense on Promox VE 6.3.3

[AdSchellevis]

The page doesn't suggest "none" is supported, but for consistency I've added it in c4e8018.