4 files changed, 8 insertions, 4 deletions
diff --git a/pkg/tcpip/header/gre.go b/pkg/tcpip/header/gre.go
index 326d03ba8..f5c52cd1b 100644
--- a/pkg/tcpip/header/gre.go
+++ b/pkg/tcpip/header/gre.go
@@ -14,6 +14,8 @@ const (
 type GRE []byte
 
 const (
+        GREHeaderSize = 4
+
 	// GREProtocolNumber is GRE's transport protocol number.
 	GREProtocolNumber tcpip.TransportProtocolNumber = 47
 )
diff --git a/pkg/tcpip/header/parse/parse.go b/pkg/tcpip/header/parse/parse.go
index de3a91227..7ac5168c7 100644
--- a/pkg/tcpip/header/parse/parse.go
+++ b/pkg/tcpip/header/parse/parse.go
@@ -175,7 +175,7 @@ func TCP(pkt *stack.PacketBuffer) bool {
 //
 // Returns true if the header was successfully parsed.
 func GRE(pkt *stack.PacketBuffer) bool {
-	_, ok := pkt.TransportHeader().Consume(4)
+	_, ok := pkt.TransportHeader().Consume(header.GREHeaderSize)
 	pkt.TransportProtocolNumber = header.GREProtocolNumber
 	return ok
 }
diff --git a/pkg/tcpip/sample/tun_tcp_connect/main.go b/pkg/tcpip/sample/tun_tcp_connect/main.go
index 138941afd..06ee5110b 100644
--- a/pkg/tcpip/sample/tun_tcp_connect/main.go
+++ b/pkg/tcpip/sample/tun_tcp_connect/main.go
@@ -156,7 +156,7 @@ func (info *GreHandlerInfo) greRead(ep *channel.Endpoint) {
         for {
                 pi, err := ep.ReadContext(context.Background());
                 linkHdr := pi.Pkt.LinkHeader()
-                greHdr := header.GRE(linkHdr.Push(4)) //header.IPv4MinimumSize + 4)
+                greHdr := header.GRE(linkHdr.Push(header.GREHeaderSize))
                 greHdr.SetProtocolType(pi.Proto)
                 log.Printf("greRead %d %v %v %v", pi.Proto, pi, err, greHdr)
                 opts := tcpip.WriteOptions{
@@ -253,7 +253,8 @@ func main() {
         // Create GRE
         greEP := grelink.New(mtu - 24)
         chEP := greEP.GetChannel()
-        greEP.NMaxHeaderLength = 4 + 20
+        // TODO detect IPv4/IPv6
+        greEP.NMaxHeaderLength = header.IPv6FixedHeaderSize + header.GREHeaderSize
 
         greInfo := GreHandlerInfo{
 //                Ep: loEP,
diff --git a/pkg/tcpip/transport/gre/protocol.go b/pkg/tcpip/transport/gre/protocol.go
index a2182cfe4..b98b5df93 100644
--- a/pkg/tcpip/transport/gre/protocol.go
+++ b/pkg/tcpip/transport/gre/protocol.go
@@ -69,7 +69,8 @@ func (p *protocol) NewRawEndpoint(netProto tcpip.NetworkProtocolNumber, waiterQu
 
 // MinimumPacketSize returns the minimum valid gre packet size.
 func (*protocol) MinimumPacketSize() int {
-	return 4 //header.GREMinimumSize
+        // TODO ?
+	return header.GREHeaderSize
 }
 
 // ParsePorts returns the source and destination ports stored in the given gre