diff --git a/src/net/sockopt_posix.go b/src/net/sockopt_posix.go
index a380c7719b..2452f06b0a 100644
--- a/src/net/sockopt_posix.go
+++ b/src/net/sockopt_posix.go
@@ -7,7 +7,6 @@
 package net
 
 import (
-	"internal/bytealg"
 	"runtime"
 	"syscall"
 )
@@ -43,35 +42,6 @@ func interfaceToIPv4Addr(ifi *Interface) (IP, error) {
 	return nil, errNoSuchInterface
 }
 
-func setIPv4MreqToInterface(mreq *syscall.IPMreq, ifi *Interface) error {
-	if ifi == nil {
-		return nil
-	}
-	ifat, err := ifi.Addrs()
-	if err != nil {
-		return err
-	}
-	for _, ifa := range ifat {
-		switch v := ifa.(type) {
-		case *IPAddr:
-			if a := v.IP.To4(); a != nil {
-				copy(mreq.Interface[:], a)
-				goto done
-			}
-		case *IPNet:
-			if a := v.IP.To4(); a != nil {
-				copy(mreq.Interface[:], a)
-				goto done
-			}
-		}
-	}
-done:
-	if bytealg.Equal(mreq.Multiaddr[:], IPv4zero.To4()) {
-		return errNoSuchMulticastInterface
-	}
-	return nil
-}
-
 func setReadBuffer(fd *netFD, bytes int) error {
 	err := fd.pfd.SetsockoptInt(syscall.SOL_SOCKET, syscall.SO_RCVBUF, bytes)
 	runtime.KeepAlive(fd)
diff --git a/src/net/sockoptip_bsdvar.go b/src/net/sockoptip4_bsdvar.go
similarity index 100%
rename from src/net/sockoptip_bsdvar.go
rename to src/net/sockoptip4_bsdvar.go
diff --git a/src/net/sockoptip_linux.go b/src/net/sockoptip4_linux.go
similarity index 68%
rename from src/net/sockoptip_linux.go
rename to src/net/sockoptip4_linux.go
index bd7d834425..8b953ebdc6 100644
--- a/src/net/sockoptip_linux.go
+++ b/src/net/sockoptip4_linux.go
@@ -9,6 +9,16 @@ import (
 	"syscall"
 )
 
+func joinIPv4Group(fd *netFD, ifi *Interface, ip IP) error {
+	mreq := &syscall.IPMreqn{Multiaddr: [4]byte{ip[0], ip[1], ip[2], ip[3]}}
+	if ifi != nil {
+		mreq.Ifindex = int32(ifi.Index)
+	}
+	err := fd.pfd.SetsockoptIPMreqn(syscall.IPPROTO_IP, syscall.IP_ADD_MEMBERSHIP, mreq)
+	runtime.KeepAlive(fd)
+	return wrapSyscallError("setsockopt", err)
+}
+
 func setIPv4MulticastInterface(fd *netFD, ifi *Interface) error {
 	var v int32
 	if ifi != nil {
diff --git a/src/net/sockoptip4_posix_nonlinux.go b/src/net/sockoptip4_posix_nonlinux.go
new file mode 100644
index 0000000000..85e8c6dcfe
--- /dev/null
+++ b/src/net/sockoptip4_posix_nonlinux.go
@@ -0,0 +1,52 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build (unix && !linux) || windows
+
+package net
+
+import (
+	"internal/bytealg"
+	"runtime"
+	"syscall"
+)
+
+func joinIPv4Group(fd *netFD, ifi *Interface, ip IP) error {
+	mreq := &syscall.IPMreq{Multiaddr: [4]byte{ip[0], ip[1], ip[2], ip[3]}}
+	if err := setIPv4MreqToInterface(mreq, ifi); err != nil {
+		return err
+	}
+	err := fd.pfd.SetsockoptIPMreq(syscall.IPPROTO_IP, syscall.IP_ADD_MEMBERSHIP, mreq)
+	runtime.KeepAlive(fd)
+	return wrapSyscallError("setsockopt", err)
+}
+
+func setIPv4MreqToInterface(mreq *syscall.IPMreq, ifi *Interface) error {
+	if ifi == nil {
+		return nil
+	}
+	ifat, err := ifi.Addrs()
+	if err != nil {
+		return err
+	}
+	for _, ifa := range ifat {
+		switch v := ifa.(type) {
+		case *IPAddr:
+			if a := v.IP.To4(); a != nil {
+				copy(mreq.Interface[:], a)
+				goto done
+			}
+		case *IPNet:
+			if a := v.IP.To4(); a != nil {
+				copy(mreq.Interface[:], a)
+				goto done
+			}
+		}
+	}
+done:
+	if bytealg.Equal(mreq.Interface[:], IPv4zero.To4()) {
+		return errNoSuchMulticastInterface
+	}
+	return nil
+}
diff --git a/src/net/sockoptip_windows.go b/src/net/sockoptip4_windows.go
similarity index 100%
rename from src/net/sockoptip_windows.go
rename to src/net/sockoptip4_windows.go
diff --git a/src/net/sockoptip_posix.go b/src/net/sockoptip6_posix.go
similarity index 74%
rename from src/net/sockoptip_posix.go
rename to src/net/sockoptip6_posix.go
index 572ea455c0..5bbc609f7b 100644
--- a/src/net/sockoptip_posix.go
+++ b/src/net/sockoptip6_posix.go
@@ -11,16 +11,6 @@ import (
 	"syscall"
 )
 
-func joinIPv4Group(fd *netFD, ifi *Interface, ip IP) error {
-	mreq := &syscall.IPMreq{Multiaddr: [4]byte{ip[0], ip[1], ip[2], ip[3]}}
-	if err := setIPv4MreqToInterface(mreq, ifi); err != nil {
-		return err
-	}
-	err := fd.pfd.SetsockoptIPMreq(syscall.IPPROTO_IP, syscall.IP_ADD_MEMBERSHIP, mreq)
-	runtime.KeepAlive(fd)
-	return wrapSyscallError("setsockopt", err)
-}
-
 func setIPv6MulticastInterface(fd *netFD, ifi *Interface) error {
 	var v int
 	if ifi != nil {