1// Copyright 2016 Google, Inc. All rights reserved.
2//
3// Use of this source code is governed by a BSD-style license
4// that can be found in the LICENSE file in the root of the source
5// tree.
6
7package layers
8
9import (
10	"encoding/binary"
11	"fmt"
12	"github.com/google/gopacket"
13)
14
15//  VXLAN is specifed in RFC 7348 https://tools.ietf.org/html/rfc7348
16//  G, D, A, Group Policy ID from https://tools.ietf.org/html/draft-smith-vxlan-group-policy-00
17//  0                   1                   2                   3
18//  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
19//  0             8               16              24              32
20// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
21// |G|R|R|R|I|R|R|R|R|D|R|R|A|R|R|R|       Group Policy ID         |
22// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
23// |     24 bit VXLAN Network Identifier           |   Reserved    |
24// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
25
26// VXLAN is a VXLAN packet header
27type VXLAN struct {
28	BaseLayer
29	ValidIDFlag      bool   // 'I' bit per RFC 7348
30	VNI              uint32 // 'VXLAN Network Identifier' 24 bits per RFC 7348
31	GBPExtension     bool   // 'G' bit per Group Policy https://tools.ietf.org/html/draft-smith-vxlan-group-policy-00
32	GBPDontLearn     bool   // 'D' bit per Group Policy
33	GBPApplied       bool   // 'A' bit per Group Policy
34	GBPGroupPolicyID uint16 // 'Group Policy ID' 16 bits per Group Policy
35}
36
37// LayerType returns LayerTypeVXLAN
38func (vx *VXLAN) LayerType() gopacket.LayerType { return LayerTypeVXLAN }
39
40func decodeVXLAN(data []byte, p gopacket.PacketBuilder) error {
41	vx := &VXLAN{}
42
43	// VNI is a 24bit number, Uint32 requires 32 bits
44	var buf [4]byte
45	copy(buf[1:], data[4:7])
46
47	// RFC 7348 https://tools.ietf.org/html/rfc7348
48	vx.ValidIDFlag = data[0]&0x08 > 0        // 'I' bit per RFC7348
49	vx.VNI = binary.BigEndian.Uint32(buf[:]) // VXLAN Network Identifier per RFC7348
50
51	// Group Based Policy https://tools.ietf.org/html/draft-smith-vxlan-group-policy-00
52	vx.GBPExtension = data[0]&0x80 > 0                       // 'G' bit per the group policy draft
53	vx.GBPDontLearn = data[1]&0x40 > 0                       // 'D' bit - the egress VTEP MUST NOT learn the source address of the encapsulated frame.
54	vx.GBPApplied = data[1]&0x80 > 0                         // 'A' bit - indicates that the group policy has already been applied to this packet.
55	vx.GBPGroupPolicyID = binary.BigEndian.Uint16(data[2:4]) // Policy ID as per the group policy draft
56
57	// Layer information
58	const vxlanLength = 8
59	vx.Contents = data[:vxlanLength]
60	vx.Payload = data[vxlanLength:]
61
62	p.AddLayer(vx)
63	return p.NextDecoder(LinkTypeEthernet)
64}
65
66// SerializeTo writes the serialized form of this layer into the
67// SerializationBuffer, implementing gopacket.SerializableLayer.
68// See the docs for gopacket.SerializableLayer for more info.
69func (vx *VXLAN) SerializeTo(b gopacket.SerializeBuffer, opts gopacket.SerializeOptions) error {
70	bytes, err := b.PrependBytes(8)
71	if err != nil {
72		return err
73	}
74
75	// PrependBytes does not guarantee that bytes are zeroed.  Setting flags via OR requires that they start off at zero
76	bytes[0] = 0
77	bytes[1] = 0
78
79	if vx.ValidIDFlag {
80		bytes[0] |= 0x08
81	}
82	if vx.GBPExtension {
83		bytes[0] |= 0x80
84	}
85	if vx.GBPDontLearn {
86		bytes[1] |= 0x40
87	}
88	if vx.GBPApplied {
89		bytes[1] |= 0x80
90	}
91
92	binary.BigEndian.PutUint16(bytes[2:4], vx.GBPGroupPolicyID)
93	if vx.VNI >= 1<<24 {
94		return fmt.Errorf("Virtual Network Identifier = %x exceeds max for 24-bit uint", vx.VNI)
95	}
96	binary.BigEndian.PutUint32(bytes[4:8], vx.VNI<<8)
97	return nil
98}
99