From 300103f2ba9e04e9510dcf394ca35432476b73a3 Mon Sep 17 00:00:00 2001 From: Jack O'Sullivan Date: Mon, 20 Jul 2026 10:57:13 +0100 Subject: [PATCH] nixos/home: Correct river wan-vlan-outer MTU to 1512 The outer WAN VLAN carries the inner VLAN's frames, whose 4B 802.1Q tag counts as payload at this layer. To fit the inner's 1508B baby-jumbo payload plus that tag it needs 1512, not 1508. Harmless before only because the physical `lan` (9000) absorbed the extra bytes; this makes the outer's MTU literally reflect what it transports. Co-Authored-By: Claude Opus 4.8 --- nixos/boxes/home/palace/vms/river.nix | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/nixos/boxes/home/palace/vms/river.nix b/nixos/boxes/home/palace/vms/river.nix index 32d34d1..26a3dd9 100644 --- a/nixos/boxes/home/palace/vms/river.nix +++ b/nixos/boxes/home/palace/vms/river.nix @@ -174,8 +174,9 @@ matchConfig.Name = "wan-vlan-outer"; vlan = [ "wan-vlan-inner" ]; networkConfig = networkd.noL3; - # baby jumbo: 1508 so the inner VLAN below can also carry it - linkConfig.MTUBytes = "1508"; + # baby jumbo: carries the inner VLAN's frames, whose 4B tag counts as payload + # at this layer, so it needs 1512 (inner's 1508B payload + the inner 802.1Q tag) + linkConfig.MTUBytes = "1512"; }; # pppd attaches PPPoE to this; just needs to be up with no L3 "71-wan-vlan-inner" = {