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// Copyright 2016 Google, Inc. All rights reserved.
//
// Use of this source code is governed by a BSD-style license
// that can be found in the LICENSE file in the root of the source
// tree.
package layers
import (
"encoding/binary"
"fmt"
"github.com/google/gopacket"
)
// VXLAN is specifed in RFC 7348 https://tools.ietf.org/html/rfc7348
// G, D, A, Group Policy ID from https://tools.ietf.org/html/draft-smith-vxlan-group-policy-00
// 0 1 2 3
// 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
// 0 8 16 24 32
// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// |G|R|R|R|I|R|R|R|R|D|R|R|A|R|R|R| Group Policy ID |
// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// | 24 bit VXLAN Network Identifier | Reserved |
// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// VXLAN is a VXLAN packet header
type VXLAN struct {
BaseLayer
ValidIDFlag bool // 'I' bit per RFC 7348
VNI uint32 // 'VXLAN Network Identifier' 24 bits per RFC 7348
GBPExtension bool // 'G' bit per Group Policy https://tools.ietf.org/html/draft-smith-vxlan-group-policy-00
GBPDontLearn bool // 'D' bit per Group Policy
GBPApplied bool // 'A' bit per Group Policy
GBPGroupPolicyID uint16 // 'Group Policy ID' 16 bits per Group Policy
}
// LayerType returns LayerTypeVXLAN
func (vx *VXLAN) LayerType() gopacket.LayerType { return LayerTypeVXLAN }
func decodeVXLAN(data []byte, p gopacket.PacketBuilder) error {
vx := &VXLAN{}
// VNI is a 24bit number, Uint32 requires 32 bits
var buf [4]byte
copy(buf[1:], data[4:7])
// RFC 7348 https://tools.ietf.org/html/rfc7348
vx.ValidIDFlag = data[0]&0x08 > 0 // 'I' bit per RFC7348
vx.VNI = binary.BigEndian.Uint32(buf[:]) // VXLAN Network Identifier per RFC7348
// Group Based Policy https://tools.ietf.org/html/draft-smith-vxlan-group-policy-00
vx.GBPExtension = data[0]&0x80 > 0 // 'G' bit per the group policy draft
vx.GBPDontLearn = data[1]&0x40 > 0 // 'D' bit - the egress VTEP MUST NOT learn the source address of the encapsulated frame.
vx.GBPApplied = data[1]&0x80 > 0 // 'A' bit - indicates that the group policy has already been applied to this packet.
vx.GBPGroupPolicyID = binary.BigEndian.Uint16(data[2:4]) // Policy ID as per the group policy draft
// Layer information
const vxlanLength = 8
vx.Contents = data[:vxlanLength]
vx.Payload = data[vxlanLength:]
p.AddLayer(vx)
return p.NextDecoder(LinkTypeEthernet)
}
// SerializeTo writes the serialized form of this layer into the
// SerializationBuffer, implementing gopacket.SerializableLayer.
// See the docs for gopacket.SerializableLayer for more info.
func (vx *VXLAN) SerializeTo(b gopacket.SerializeBuffer, opts gopacket.SerializeOptions) error {
bytes, err := b.PrependBytes(8)
if err != nil {
return err
}
// PrependBytes does not guarantee that bytes are zeroed. Setting flags via OR requires that they start off at zero
bytes[0] = 0
bytes[1] = 0
if vx.ValidIDFlag {
bytes[0] |= 0x08
}
if vx.GBPExtension {
bytes[0] |= 0x80
}
if vx.GBPDontLearn {
bytes[1] |= 0x40
}
if vx.GBPApplied {
bytes[1] |= 0x80
}
binary.BigEndian.PutUint16(bytes[2:4], vx.GBPGroupPolicyID)
if vx.VNI >= 1<<24 {
return fmt.Errorf("Virtual Network Identifier = %x exceeds max for 24-bit uint", vx.VNI)
}
binary.BigEndian.PutUint32(bytes[4:8], vx.VNI<<8)
return nil
}