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