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105 lines
3.7 KiB
Go
105 lines
3.7 KiB
Go
// Copyright (c) Tailscale Inc & AUTHORS
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// SPDX-License-Identifier: BSD-3-Clause
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package packet
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import (
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"encoding/binary"
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"errors"
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"io"
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)
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const (
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// GeneveFixedHeaderLength is the length of the fixed size portion of the
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// Geneve header, in bytes.
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GeneveFixedHeaderLength = 8
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)
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const (
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// GeneveProtocolDisco is the IEEE 802 Ethertype number used to represent
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// the Tailscale Disco protocol in a Geneve header.
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GeneveProtocolDisco uint16 = 0x7A11
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// GeneveProtocolWireGuard is the IEEE 802 Ethertype number used to represent the
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// WireGuard protocol in a Geneve header.
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GeneveProtocolWireGuard uint16 = 0x7A12
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)
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// GeneveHeader represents the fixed size Geneve header from RFC8926.
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// TLVs/options are not implemented/supported.
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//
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// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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// |Ver| Opt Len |O|C| Rsvd. | Protocol Type |
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// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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// | Virtual Network Identifier (VNI) | Reserved |
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// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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type GeneveHeader struct {
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// Ver (2 bits): The current version number is 0. Packets received by a
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// tunnel endpoint with an unknown version MUST be dropped. Transit devices
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// interpreting Geneve packets with an unknown version number MUST treat
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// them as UDP packets with an unknown payload.
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Version uint8
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// Protocol Type (16 bits): The type of protocol data unit appearing after
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// the Geneve header. This follows the Ethertype [ETYPES] convention, with
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// Ethernet itself being represented by the value 0x6558.
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Protocol uint16
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// Virtual Network Identifier (VNI) (24 bits): An identifier for a unique
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// element of a virtual network. In many situations, this may represent an
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// L2 segment; however, the control plane defines the forwarding semantics
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// of decapsulated packets. The VNI MAY be used as part of ECMP forwarding
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// decisions or MAY be used as a mechanism to distinguish between
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// overlapping address spaces contained in the encapsulated packet when load
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// balancing across CPUs.
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VNI uint32
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// O (1 bit): Control packet. This packet contains a control message.
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// Control messages are sent between tunnel endpoints. Tunnel endpoints MUST
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// NOT forward the payload, and transit devices MUST NOT attempt to
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// interpret it. Since control messages are less frequent, it is RECOMMENDED
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// that tunnel endpoints direct these packets to a high-priority control
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// queue (for example, to direct the packet to a general purpose CPU from a
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// forwarding Application-Specific Integrated Circuit (ASIC) or to separate
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// out control traffic on a NIC). Transit devices MUST NOT alter forwarding
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// behavior on the basis of this bit, such as ECMP link selection.
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Control bool
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}
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// Encode encodes GeneveHeader into b. If len(b) < GeneveFixedHeaderLength an
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// io.ErrShortBuffer error is returned.
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func (h *GeneveHeader) Encode(b []byte) error {
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if len(b) < GeneveFixedHeaderLength {
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return io.ErrShortBuffer
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}
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if h.Version > 3 {
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return errors.New("version must be <= 3")
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}
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b[0] = 0
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b[1] = 0
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b[0] |= h.Version << 6
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if h.Control {
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b[1] |= 0x80
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}
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binary.BigEndian.PutUint16(b[2:], h.Protocol)
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if h.VNI > 1<<24-1 {
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return errors.New("VNI must be <= 2^24-1")
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}
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binary.BigEndian.PutUint32(b[4:], h.VNI<<8)
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return nil
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}
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// Decode decodes GeneveHeader from b. If len(b) < GeneveFixedHeaderLength an
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// io.ErrShortBuffer error is returned.
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func (h *GeneveHeader) Decode(b []byte) error {
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if len(b) < GeneveFixedHeaderLength {
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return io.ErrShortBuffer
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}
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h.Version = b[0] >> 6
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if b[1]&0x80 != 0 {
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h.Control = true
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}
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h.Protocol = binary.BigEndian.Uint16(b[2:])
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h.VNI = binary.BigEndian.Uint32(b[4:]) >> 8
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return nil
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}
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