diff --git a/cmd/containerboot/main.go b/cmd/containerboot/main.go
index 1a11c3150..705b73bc6 100644
--- a/cmd/containerboot/main.go
+++ b/cmd/containerboot/main.go
@@ -129,6 +129,7 @@ import (
 	"os/signal"
 	"path/filepath"
 	"slices"
+	"strconv"
 	"strings"
 	"sync"
 	"sync/atomic"
@@ -147,6 +148,7 @@ import (
 	klc "tailscale.com/kube/localclient"
 	"tailscale.com/kube/metrics"
 	"tailscale.com/kube/services"
+	"tailscale.com/net/tsaddr"
 	"tailscale.com/tailcfg"
 	"tailscale.com/types/logger"
 	"tailscale.com/types/netmap"
@@ -995,7 +997,8 @@ func fetchNetMap(ctx context.Context, lc *local.Client) (*netmap.NetworkMap, err
 }
 
 // resolveTailnetFQDN resolves a tailnet FQDN to a list of IP prefixes, which
-// can be either a peer device or a Tailscale Service.
+// can be either a peer device, a Tailscale Service, or a 4via6 synthesized
+// DNS name (e.g. "10-1-0-5-via-7.tailnet.ts.net").
 func resolveTailnetFQDN(nm *netmap.NetworkMap, fqdn string) ([]netip.Prefix, error) {
 	dnsFQDN, err := dnsname.ToFQDN(fqdn)
 	if err != nil {
@@ -1014,6 +1017,19 @@ func resolveTailnetFQDN(nm *netmap.NetworkMap, fqdn string) ([]netip.Prefix, err
 		return svcIPs, nil
 	}
 
+	// If not found yet, check for a matching 4via6 DNS name.
+	if addr, ok := resolveViaDomain(dnsFQDN); ok {
+		prefix := netip.PrefixFrom(addr, addr.BitLen())
+		for _, nn := range nm.Peers {
+			for _, allowedIP := range nn.AllowedIPs().All() {
+				if allowedIP.Contains(addr) {
+					return []netip.Prefix{prefix}, nil
+				}
+			}
+		}
+		return nil, fmt.Errorf("resolved 4via6 address %v for %q but no peer advertises a route containing it", addr, fqdn)
+	}
+
 	return nil, fmt.Errorf("could not find Tailscale node or service %q; it either does not exist, or not reachable because of ACLs", fqdn)
 }
 
@@ -1055,3 +1071,40 @@ func serviceIPsFromNetMap(nm *netmap.NetworkMap, fqdn dnsname.FQDN) []netip.Pref
 
 	return prefixes
 }
+
+// resolveViaDomain parses an FQDN as a 4via6 in the format "<ipv4-with-hyphens>-via-<siteID>[.domain]"
+// and returns the IPv6 via address.
+// This borrows heavily from net/dns/resolver.(*Resolver).resolveViaDomain.
+// TODO(beckypauley): consider a refactor of the above to remove duplication.
+func resolveViaDomain(fqdn dnsname.FQDN) (netip.Addr, bool) {
+	// The minimum length of a valid 4via6 FQDN i.e. "via-X.0.0.0.0".
+	const minFQDNLength = 13
+	name := string(fqdn.WithoutTrailingDot())
+	// This is not a  fqdn.
+	if !strings.Contains(name, "-via-") {
+		return netip.Addr{}, false
+	}
+	if len(name) < minFQDNLength {
+		return netip.Addr{}, false // too short to be valid
+	}
+	firstLabel, domain, _ := strings.Cut(name, ".")
+	if !(domain == "" || dnsname.HasSuffix(domain, "ts.net") || dnsname.HasSuffix(domain, "tailscale.net")) {
+		return netip.Addr{}, false
+	}
+	v4hyphens, siteIDStr, ok := strings.Cut(firstLabel, "-via-")
+	if !ok {
+		return netip.Addr{}, false
+	}
+	ip4Str := strings.ReplaceAll(v4hyphens, "-", ".")
+	ip4, err := netip.ParseAddr(ip4Str)
+	if err != nil || !ip4.Is4() {
+		return netip.Addr{}, false
+	}
+	siteID, err := strconv.ParseUint(siteIDStr, 0, 32)
+	if err != nil {
+		return netip.Addr{}, false
+	}
+	// MapVia will never error when given an IPv4 netip.Prefix.
+	out, _ := tsaddr.MapVia(uint32(siteID), netip.PrefixFrom(ip4, ip4.BitLen()))
+	return out.Addr(), true
+}
diff --git a/cmd/k8s-operator/connector.go b/cmd/k8s-operator/connector.go
index 0c2d32482..323dc7b86 100644
--- a/cmd/k8s-operator/connector.go
+++ b/cmd/k8s-operator/connector.go
@@ -29,6 +29,8 @@ import (
 	tsoperator "tailscale.com/k8s-operator"
 	tsapi "tailscale.com/k8s-operator/apis/v1alpha1"
 	"tailscale.com/kube/kubetypes"
+	"tailscale.com/net/netutil"
+	"tailscale.com/net/tsaddr"
 	"tailscale.com/tstime"
 	"tailscale.com/util/clientmetric"
 	"tailscale.com/util/set"
@@ -356,6 +358,11 @@ func validateRoutes(routes tsapi.Routes) error {
 		if pfx.Masked() != pfx {
 			errs = append(errs, fmt.Errorf("route %s has non-address bits set; expected %s", pfx, pfx.Masked()))
 		}
+		if tsaddr.IsViaPrefix(pfx) {
+			if err := netutil.ValidateViaPrefix(pfx); err != nil {
+				errs = append(errs, err)
+			}
+		}
 	}
 	return errors.Join(errs...)
 }
diff --git a/cmd/k8s-operator/connector_test.go b/cmd/k8s-operator/connector_test.go
index 69e8e287d..b366dac38 100644
--- a/cmd/k8s-operator/connector_test.go
+++ b/cmd/k8s-operator/connector_test.go
@@ -145,6 +145,22 @@ func TestConnector(t *testing.T) {
 	expectReconciled(t, cr, "", "test")
 	expectEqual(t, fc, expectedSTS(t, fc, opts), removeResourceReqs)
 
+	// Set an invalid 4via6 route (site ID too large).
+	mustUpdate[tsapi.Connector](t, fc, "", "test", func(conn *tsapi.Connector) {
+		conn.Spec.SubnetRouter.AdvertiseRoutes = []tsapi.Route{"fd7a:115c:a1e0:b1a:1:0:a2c:0/116"}
+	})
+	expectReconciled(t, cr, "", "test")
+	// STS should still have the previous valid route, unchanged.
+	expectEqual(t, fc, expectedSTS(t, fc, opts), removeResourceReqs)
+
+	// Set a valid 4via6 route.
+	mustUpdate[tsapi.Connector](t, fc, "", "test", func(conn *tsapi.Connector) {
+		conn.Spec.SubnetRouter.AdvertiseRoutes = []tsapi.Route{"fd7a:115c:a1e0:b1a:0:1:a2c:0/116"}
+	})
+	opts.subnetRoutes = "fd7a:115c:a1e0:b1a:0:1:a2c:0/116"
+	expectReconciled(t, cr, "", "test")
+	expectEqual(t, fc, expectedSTS(t, fc, opts), removeResourceReqs)
+
 	// Delete the Connector.
 	if err = fc.Delete(context.Background(), cn); err != nil {
 		t.Fatalf("error deleting Connector: %v", err)
diff --git a/net/netutil/routes.go b/net/netutil/routes.go
index 26f2de97c..510572b6d 100644
--- a/net/netutil/routes.go
+++ b/net/netutil/routes.go
@@ -13,7 +13,11 @@ import (
 	"tailscale.com/net/tsaddr"
 )
 
-func validateViaPrefix(ipp netip.Prefix) error {
+// ValidateViaPrefix checks that the IP prefix is a valid 4via6 route.
+// It verifies that the prefix is in the Tailscale via range, has a prefix
+// length between /96 and /128, and that the embedded site ID is in the
+// range 0–65535.
+func ValidateViaPrefix(ipp netip.Prefix) error {
 	if !tsaddr.IsViaPrefix(ipp) {
 		return fmt.Errorf("%v is not a 4-in-6 prefix", ipp)
 	}
@@ -51,7 +55,7 @@ func CalcAdvertiseRoutes(advertiseRoutes string, advertiseDefaultRoute bool) ([]
 				return nil, fmt.Errorf("%s has non-address bits set; expected %s", ipp, ipp.Masked())
 			}
 			if tsaddr.IsViaPrefix(ipp) {
-				if err := validateViaPrefix(ipp); err != nil {
+				if err := ValidateViaPrefix(ipp); err != nil {
 					return nil, err
 				}
 			}