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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"
"errors"
"net"
"github.com/google/gopacket"
)
/*
This layer provides decoding for Virtual Router Redundancy Protocol (VRRP) v2.
https://tools.ietf.org/html/rfc3768#section-5
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version| Type | Virtual Rtr ID| Priority | Count IP Addrs|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Auth Type | Adver Int | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP Address (1) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| . |
| . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP Address (n) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Authentication Data (1) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Authentication Data (2) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
*/
type VRRPv2Type uint8
type VRRPv2AuthType uint8
const (
VRRPv2Advertisement VRRPv2Type = 0x01 // router advertisement
)
// String conversions for VRRP message types
func (v VRRPv2Type) String() string {
switch v {
case VRRPv2Advertisement:
return "VRRPv2 Advertisement"
default:
return ""
}
}
const (
VRRPv2AuthNoAuth VRRPv2AuthType = 0x00 // No Authentication
VRRPv2AuthReserved1 VRRPv2AuthType = 0x01 // Reserved field 1
VRRPv2AuthReserved2 VRRPv2AuthType = 0x02 // Reserved field 2
)
func (v VRRPv2AuthType) String() string {
switch v {
case VRRPv2AuthNoAuth:
return "No Authentication"
case VRRPv2AuthReserved1:
return "Reserved"
case VRRPv2AuthReserved2:
return "Reserved"
default:
return ""
}
}
// VRRPv2 represents an VRRP v2 message.
type VRRPv2 struct {
BaseLayer
Version uint8 // The version field specifies the VRRP protocol version of this packet (v2)
Type VRRPv2Type // The type field specifies the type of this VRRP packet. The only type defined in v2 is ADVERTISEMENT
VirtualRtrID uint8 // identifies the virtual router this packet is reporting status for
Priority uint8 // specifies the sending VRRP router's priority for the virtual router (100 = default)
CountIPAddr uint8 // The number of IP addresses contained in this VRRP advertisement.
AuthType VRRPv2AuthType // identifies the authentication method being utilized
AdverInt uint8 // The Advertisement interval indicates the time interval (in seconds) between ADVERTISEMENTS. The default is 1 second
Checksum uint16 // used to detect data corruption in the VRRP message.
IPAddress []net.IP // one or more IP addresses associated with the virtual router. Specified in the CountIPAddr field.
}
// LayerType returns LayerTypeVRRP for VRRP v2 message.
func (v *VRRPv2) LayerType() gopacket.LayerType { return LayerTypeVRRP }
func (v *VRRPv2) DecodeFromBytes(data []byte, df gopacket.DecodeFeedback) error {
v.BaseLayer = BaseLayer{Contents: data[:len(data)]}
v.Version = data[0] >> 4 // high nibble == VRRP version. We're expecting v2
v.Type = VRRPv2Type(data[0] & 0x0F) // low nibble == VRRP type. Expecting 1 (advertisement)
if v.Type != 1 {
// rfc3768: A packet with unknown type MUST be discarded.
return errors.New("Unrecognized VRRPv2 type field.")
}
v.VirtualRtrID = data[1]
v.Priority = data[2]
v.CountIPAddr = data[3]
if v.CountIPAddr < 1 {
return errors.New("VRRPv2 number of IP addresses is not valid.")
}
v.AuthType = VRRPv2AuthType(data[4])
v.AdverInt = uint8(data[5])
v.Checksum = binary.BigEndian.Uint16(data[6:8])
// populate the IPAddress field. The number of addresses is specified in the v.CountIPAddr field
// offset references the starting byte containing the list of ip addresses
offset := 8
for i := uint8(0); i < v.CountIPAddr; i++ {
v.IPAddress = append(v.IPAddress, data[offset:offset+4])
offset += 4
}
// any trailing packets here may be authentication data and *should* be ignored in v2 as per RFC
//
// 5.3.10. Authentication Data
//
// The authentication string is currently only used to maintain
// backwards compatibility with RFC 2338. It SHOULD be set to zero on
// transmission and ignored on reception.
return nil
}
// CanDecode specifies the layer type in which we are attempting to unwrap.
func (v *VRRPv2) CanDecode() gopacket.LayerClass {
return LayerTypeVRRP
}
// NextLayerType specifies the next layer that should be decoded. VRRP does not contain any further payload, so we set to 0
func (v *VRRPv2) NextLayerType() gopacket.LayerType {
return gopacket.LayerTypeZero
}
// The VRRP packet does not include payload data. Setting byte slice to nil
func (v *VRRPv2) Payload() []byte {
return nil
}
// decodeVRRP will parse VRRP v2
func decodeVRRP(data []byte, p gopacket.PacketBuilder) error {
if len(data) < 8 {
return errors.New("Not a valid VRRP packet. Packet length is too small.")
}
v := &VRRPv2{}
return decodingLayerDecoder(v, data, p)
}
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