@ -17,6 +17,7 @@ import (
"net/http"
"net/http"
"net/netip"
"net/netip"
"net/url"
"net/url"
"runtime"
"sort"
"sort"
"strings"
"strings"
"sync"
"sync"
@ -740,18 +741,37 @@ func (f *forwarder) sendUDP(ctx context.Context, fq *forwardQuery, rr resolverAn
return out , nil
return out , nil
} }
var optDNSForwardUseRoutes = envknob . RegisterOptBool ( "TS_DNS_FORWARD_USE_ROUTES" )
// ShouldUseRoutes reports true if the DNS resolver should use the peer or system dialer
// for forwarding DNS queries to upstream nameservers via TCP, based on the destination
// address and configured routes. Currently, this requires maintaining a [bart.Table],
// resulting in a slightly higher memory usage.
//
// It reports false if the system dialer should always be used, regardless of the
// destination address.
//
// TODO(nickkhyl): Update [tsdial.Dialer] to reuse the bart.Table we create in net/tstun.Wrapper
// to avoid having two bart tables in memory, especially on iOS. Once that's done,
// we can get rid of the nodeAttr/control knob and always use UserDial for DNS.
//
// See https://github.com/tailscale/tailscale/issues/12027.
func ShouldUseRoutes ( knobs * controlknobs . Knobs ) bool {
switch runtime . GOOS {
case "android" , "ios" :
// On mobile platforms with lower memory limits (e.g., 50MB on iOS),
// this behavior is still gated by the "user-dial-routes" nodeAttr.
return knobs != nil && knobs . UserDialUseRoutes . Load ( )
default :
// On all other platforms, it is the default behavior,
// but it can be overridden with the "TS_DNS_FORWARD_USE_ROUTES" env var.
doNotUseRoutes := optDNSForwardUseRoutes ( ) . EqualBool ( false )
return ! doNotUseRoutes
}
}
func ( f * forwarder ) getDialerType ( ) netx . DialFunc { func ( f * forwarder ) getDialerType ( ) netx . DialFunc {
if f . controlKnobs != nil && f . controlKnobs . UserDialUseRoutes . Load ( ) {
if ShouldUseRoutes ( f . controlKnobs ) {
// It is safe to use UserDial as it dials external servers without going through Tailscale
// and closes connections on interface change in the same way as SystemDial does,
// thus preventing DNS resolution issues when switching between WiFi and cellular,
// but can also dial an internal DNS server on the Tailnet or via a subnet router.
//
// TODO(nickkhyl): Update tsdial.Dialer to reuse the bart.Table we create in net/tstun.Wrapper
// to avoid having two bart tables in memory, especially on iOS. Once that's done,
// we can get rid of the nodeAttr/control knob and always use UserDial for DNS.
//
// See https://github.com/tailscale/tailscale/issues/12027.
return f . dialer . UserDial
return f . dialer . UserDial
}
}
return f . dialer . SystemDial
return f . dialer . SystemDial
Nick Khyl
7 months ago
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