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Derive LAN subnets and validate addressing at build time

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Add an IPv4 helper lib (parse, netmask, cidr, overlap) and derive
router.lans.<name>.ipv4.subnet from address and prefixLength instead of
requiring it twice. New assertions reject invalid addresses, DHCP pools that
are reversed, outside the subnet or contain the router address, and
overlapping LANs.

Add `lib` unit tests and an `assertions` check that evaluates broken configs
and compares the exact error messages.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
This commit is contained in:
nils
2026-10-27 15:00:24 +01:00
co-authored by Claude Sonnet 5.5
parent 0ba4d49766
commit 96e5b7b859
9 changed files with 362 additions and 47 deletions
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modules/router/options.nix
+52 -41
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@@ -1,6 +1,7 @@
{ lib, ... }:
let
inherit (lib) mkOption mkEnableOption types;
rlib = import ./lib.nix { inherit lib; };
in
{
options.router = {
@@ -18,55 +19,65 @@ in
default = { };
description = "LAN segments served by this router, keyed by name.";
type = types.attrsOf (
types.submodule {
options = {
interface = mkOption {
type = types.str;
example = "eth1";
description = "Interface (or bridge/VLAN device) carrying this LAN.";
};
ipv4 = {
address = mkOption {
types.submodule (
{ config, ... }:
{
options = {
interface = mkOption {
type = types.str;
example = "192.168.10.1";
description = "Router address on this LAN.";
example = "eth1";
description = "Interface (or bridge/VLAN device) carrying this LAN.";
};
prefixLength = mkOption {
type = types.ints.between 8 30;
default = 24;
};
subnet = mkOption {
type = types.str;
example = "192.168.10.0/24";
description = "Network in CIDR notation; must contain `address`.";
};
};
dhcp = {
enable = mkOption {
ipv4 = {
address = mkOption {
type = types.str;
example = "192.168.10.1";
description = "Router address on this LAN.";
};
prefixLength = mkOption {
type = types.ints.between 8 30;
default = 24;
};
subnet = mkOption {
type = types.str;
readOnly = true;
description = "Network in CIDR notation, derived from `address` and `prefixLength`.";
};
};
dhcp = {
enable = mkOption {
type = types.bool;
default = true;
};
pool = {
start = mkOption {
type = types.str;
example = "192.168.10.100";
};
end = mkOption {
type = types.str;
example = "192.168.10.199";
};
};
};
allowManagement = mkOption {
type = types.bool;
default = true;
};
pool = {
start = mkOption {
type = types.str;
example = "192.168.10.100";
};
end = mkOption {
type = types.str;
example = "192.168.10.199";
};
description = "Whether clients on this LAN may reach SSH on the router.";
};
};
allowManagement = mkOption {
type = types.bool;
default = true;
description = "Whether clients on this LAN may reach SSH on the router.";
};
};
}
# "invalid" is only ever seen when assertions.nix is already failing.
config.ipv4.subnet =
if rlib.ipv4.parse config.ipv4.address == null then
"invalid"
else
rlib.ipv4.cidr config.ipv4.address config.ipv4.prefixLength;
}
)
);
};