TUN-6339: Add config for IPv6 support

cmd/cloudflared/tunnel/cmd.go

@@ -514,6 +514,12 @@ func tunnelFlags(shouldHide bool) []cli.Flag {
 			Usage:   "Cloudflare Edge region to connect to. Omit or set to empty to connect to the global region.",
 			EnvVars: []string{"TUNNEL_REGION"},
 		}),
+		altsrc.NewStringFlag(&cli.StringFlag{
+			Name:    "edge-ip-version",
+			Usage:   "Cloudflare Edge ip address version to connect with. {4, 6, auto}",
+			EnvVars: []string{"TUNNEL_EDGE_IP_VERSION"},
+			Hidden:  true,
+		}),
 		altsrc.NewStringFlag(&cli.StringFlag{
 			Name:    tlsconfig.CaCertFlag,
 			Usage:   "Certificate Authority authenticating connections with Cloudflare's edge network.",

cmd/cloudflared/tunnel/configuration.go

@@ -18,6 +18,7 @@ import (
 	"golang.org/x/crypto/ssh/terminal"
 
 	"github.com/cloudflare/cloudflared/cmd/cloudflared/cliutil"
+	"github.com/cloudflare/cloudflared/edgediscovery/allregions"
 
 	"github.com/cloudflare/cloudflared/config"
 	"github.com/cloudflare/cloudflared/connection"
@@ -324,6 +325,10 @@ func prepareTunnelConfig(
 		CompressionSetting: h2mux.CompressionSetting(uint64(c.Int("compression-quality"))),
 		MetricsUpdateFreq:  c.Duration("metrics-update-freq"),
 	}
+	edgeIPVersion, err := parseConfigIPVersion(c.String("edge-ip-version"))
+	if err != nil {
+		return nil, nil, err
+	}
 
 	tunnelConfig := &supervisor.TunnelConfig{
 		GracePeriod:     gracePeriod,
@@ -332,6 +337,7 @@ func prepareTunnelConfig(
 		ClientID:        clientID,
 		EdgeAddrs:       c.StringSlice("edge"),
 		Region:          c.String("region"),
+		EdgeIPVersion:   edgeIPVersion,
 		HAConnections:   c.Int("ha-connections"),
 		IncidentLookup:  supervisor.NewIncidentLookup(),
 		IsAutoupdated:   c.Bool("is-autoupdated"),
@@ -404,3 +410,18 @@ func dedup(slice []string) []string {
 	}
 	return keys
 }
+
+// ParseConfigIPVersion returns the IP version from possible expected values from config
+func parseConfigIPVersion(version string) (v allregions.ConfigIPVersion, err error) {
+	switch version {
+	case "4":
+		v = allregions.IPv4Only
+	case "6":
+		v = allregions.IPv6Only
+	case "auto":
+		v = allregions.Auto
+	default: // unspecified or invalid
+		err = fmt.Errorf("invalid value for edge-ip-version: %s", version)
+	}
+	return
+}