What is 100.100.100.100?
100.100.100.100 or Quad100 is a special Tailscale IP address in your Tailscale network (known as a tailnet) that provides essential local services. It operates similarly to the localhost address (127.0.0.1) but serves only Tailscale-specific services and has network-aware functionality. These services include a DNS resolver and a device management interface.
Quad100 operates as a device-local service, meaning local traffic connecting to 100.100.100.100 doesn’t leave your device unless it’s necessary to provide a service, such as when forwarding DNS requests. Other devices cannot access your device using 100.100.100.100, and Tailscale has no visibility over its contents.
Quad100 also has the IPv6 address fd7a:115c:a1e0::53.
DNS resolver
One of the services provided by Quad100 is a DNS resolver running on port 53 (100.100.100.100:53). A DNS resolver is a service that translates IP addresses to hostnames like google.com or macbook.tailnetname.ts.net. Quad100 is a stub resolver, similar to systemd-resolved, except with extra features.
The Quad100 DNS resolver resolves hostnames in your tailnet locally using MagicDNS and forwards DNS requests to exit nodes (when configured). It also provides DNS-over-HTTPS (DoH) encryption when available and implements settings like overriding local DNS and split DNS (for Android).
While Quad100's DNS resolver operates locally without logging, forwarded requests might be logged by configured nameservers.
Device management interface
Quad100 provides a device management interface on port 80. The interface lets you configure settings for the local device from a web browser. These include device-specific settings, exit node settings, Tailscale SSH settings, and subnet routes.
You can access the interface at http://100.100.100.100 locally, even if your device doesn't have a native Tailscale client.
For Tailscale v1.64.0 and later, the device management interface is enabled by default. For earlier versions, you can enable it manually.