feat: auto-detect WireGuard MTU from underlay interface #406
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Change the --mtu flag default from a fixed 1420 to "auto", which detects the MTU of the underlay network interface and subtracts the WireGuard overhead (80 bytes) to calculate the optimal WireGuard interface MTU. This is particularly useful in multi-cloud deployments where different locations may have different underlay MTUs (e.g. 1500 on bare metal vs 1400 on Azure). The MTU is re-detected on each reconciliation loop to handle interface changes. The flag still accepts numeric values for manual override. Co-Authored-By: Claude <noreply@anthropic.com> Signed-off-by: Andrei Kvapil <kvapss@gmail.com>
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Summary
--mtuflag default from a fixed1420to"auto", which detects the MTU of the underlay network interface and subtracts the WireGuard overhead (80 bytes)Motivation
In multi-cloud deployments, different locations may have different underlay MTUs (e.g. 1500 on bare metal vs 1400 on Azure). A fixed MTU causes packet fragmentation or drops when the underlay MTU is smaller than expected. Auto-detection eliminates the need for per-node MTU configuration.
Changes
pkg/wireguard/wireguard.go: AddWireGuardOverheadconstant (80 bytes) andSetMTU()helperpkg/mesh/mesh.go: AdddetectMTU()function,mtu/autoMTUfields, MTU re-detection inapplyTopology()cmd/kg/main.go: Change--mtuflag fromuinttostringwith"auto"default