Dan [the] Salmon | Windows Kills SMB Speeds When Using Tailscale
The NAS can definitely saturate a gigabit link which is what my desktop connects to the switch over. I had seen this behavior before and had a feeling it was related to having Tailscale running - the last time it happened I quit Tailscale and my fast transfers returned.
Well, in my home network I have a Proxmox VM that, among other things, runs Tailscale as a subnet router. I set it up this way so that my homelab services (especially Pi-hole) are available to my laptop and phone from outside my house.
Consequently, my desktop now has 2 interfaces that can both reach my trusted 10.10.1.1/24 network - the gigabit NIC connected to the switch and the Tailscale virtual adapter.
I learned that Windows has a system for determining which interface will handle a request when multiple interfaces could be used. Just like dynamic routing protocols calculate the “cost” of each route to a remote network, Windows has a system to calculate which interface to use. Windows refers to this cost as the “Interface Metric” which is calculated based on the physical interface medium and its link speed (as documented here in the last table).
Since the Tailscale interface advertises a link speed of 100Gbps, Windows assigns it a much lower interface metric than the integrated gigabit NIC on my motherboard. Lower metric = lower “cost” associated.
