Generic Protocol Extension for VXLAN (VXLAN-GPE)

3.1. VXLAN-GPE Header

 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|R|R|Ver|I|P|B|O|       Reserved                |Next Protocol  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                VXLAN Network Identifier (VNI) |   Reserved    |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Flags (8 bits):

The first 8 bits of the header are the flag field. The bits designated "R" above are reserved flags. These MUST be set to zero on transmission and ignored on receipt.¶

Version (Ver):

Indicates VXLAN-GPE protocol version. The initial version is 0. If a receiver does not support the version indicated it MUST drop the packet.¶

Instance Bit (I bit):

The I bit MUST be set to indicate a valid VNI.¶

Next Protocol Bit (P bit):

The P bit is set to indicate that the Next Protocol field is present.¶

BUM Traffic Bit (B bit):

The B bit is set to indicate that this is ingress-replicated BUM Traffic (ie, Broadcast, Unknown unicast, or Multicast).¶

OAM Flag Bit (O bit):

The O bit is set to indicate that the packet is an OAM packet.¶

Next Protocol:

This 8 bit field indicates the protocol header immediately following the VXLAN-GPE header.¶

VNI:

This 24 bit field identifies the VXLAN overlay network the inner packet belongs to. Inner packets belonging to different VNIs cannot communicate with each other (unless explicitly allowed by policy).¶

Reserved:

Reserved fields MUST be set to zero on transmission and ignored on receipt.¶

3.2. Multi Protocol Support

This draft defines the following two changes to the VXLAN header in order to support multi-protocol encapsulation:¶

P Bit:

Flag bit 5 is defined as the Next Protocol bit. The P bit MUST be set to 1 to indicate the presence of the 8 bit next protocol field.¶

When UDP dest port=4790, P = 0 the "Next Protocol" field must be set to zero and the payload MUST be ETHERNET(L2) as defined by [RFC7348].¶

Flag bit 5 was chosen as the P bit because this flag bit is currently reserved in VXLAN.¶

Next Protocol Field:

When the P-bit is set to 1, the lower 8 bits of the first word are used to carry a Next Protocol. This 'Next Protocol' field contains the protocol of the encapsulated payload packet. Values are tracked by the IANA "LISP-GPE Next Protocol" registry, defined in Section 6.1 of [RFC9305], that VXLAN-GPE shares with the LISP-GPE protocol. At the time this document is edited the IANA "LISP-GPE Next Protocol" registry specifies the following Next Protocol values:¶

0x00 :

Reserved¶

0x01 :

IPv4¶

0x02 :

IPv6¶

0x03 :

Ethernet¶

0x04 :

Network Service Header [RFC8300]¶

0x05 to 0x7D:

Unassigned¶

0x7E, 0x7F:

Experimentation and testing¶

0x80 to 0xFD:

Unassigned (shim headers)¶

0xFE, 0xFF:

Experimentation and testing (shim headers)¶

Next protocol values 0x7E, 0x7F and 0xFE, 0xFF are assigned for experimentation and testing as per [RFC3692].¶

Next protocol values from Ox80 to 0xFD are assigned to protocols encoded as generic shim headers. All shim protocols MUST use the header structure in Figure 3, which includes a 'Next Protocol' field. When shim headers are used with other protocols identified by Next Protocol values from 0x0 to 0x7F, all the shim headers MUST come first.¶

Shim headers can be used to incrementally deploy new GPE features, keeping the processing of shim headers known to a given VTEP implementation in the 'fast' path (typically an Application- Specific Integrated Circuit (ASIC)) while punting the processing of the remaining new GPE features to the 'slow' path.¶

Shim protocols MUST have the first 32 bits defined as:¶

 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     Type      |    Length     |   Reserved    | Next Protocol |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                                                               |
~                    Protocol Specific Fields                   ~
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Where:¶

Type:

This field identifies the different messages of this protocol.¶

Length:

This field indicates the length, in in 4-octet units, of this protocol message not including the first 4 octets.¶

Reserved:

The use of this field is reserved to the protocol defined in this message.¶

Next Protocol Field:

This field contains the protocol of the encapsulated payload. The values are tracked in the IANA "LISP-GPE Next Protocol" registry, defined in Section 6.1 of [RFC9305].¶

3.3. Replicated BUM Traffic

Flag bit 6 is defined as the B bit. When the B bit is set to 1, the packet is marked as an an ingress-replicated BUM Traffic (i.e. Broadcast, Unknown unicast, or Multicast) to help egress VTEP to differentiate between known and unknown unicast. The details of using the B bit are out of scope for this document, but please see [RFC8365] for an example in the EVPN context. As with the P-bit, bit 6 is currently a reserved flag in VXLAN.¶

3.4. OAM Support

Flag bit 7 is defined as the O bit. When the O bit is set to 1, the packet is an OAM packet and OAM processing MUST occur. Other header fields including Next Protocol MUST adhere to the definitions in Section 3. The OAM protocol details are out of scope for this document. As with the P-bit, bit 7 is currently a reserved flag in VXLAN.¶

3.5. Version Bits

VXLAN-GPE bits 2 and 3 are defined as version bits. These bits are reserved in VXLAN. The version field is used to ensure backward compatibility going forward with future VXLAN-GPE updates.¶

The initial version for VXLAN-GPE is 0.¶

6.1. VXLAN VTEP to VXLAN-GPE VTEP

A VXLAN VTEP conforms to VXLAN frame format and uses UDP destination port 4789 when sending traffic to VXLAN-GPE VTEP. As per VXLAN, reserved bits 5 and 7, VXLAN-GPE P and O-bits respectively must be set to zero. The remaining reserved bits must be zero, including the VXLAN-GPE version field, bits 2 and 3. The encapsulated payload MUST be Ethernet.¶

6.2. VXLAN-GPE VTEP to VXLAN VTEP

A VXLAN-GPE VTEP MUST NOT encapsulate non-Ethernet frames to a VXLAN VTEP. When encapsulating Ethernet frames to a VXLAN VTEP, the VXLAN-GPE VTEP MUST conform to VXLAN frame format and hence will set the P bit to 0, the Next Protocol to 0 and use UDP destination port 4789. A VXLAN-GPE VTEP MUST also set O = 0 and Ver = 0 when encapsulating Ethernet frames to VXLAN VTEP. The receiving VXLAN VTEP will treat this packet as a VXLAN packet.¶

A method for determining the capabilities of a VXLAN VTEP (GPE or non-GPE) is out of the scope of this draft.¶

6.3. VXLAN-GPE UDP Ports

VXLAN-GPE uses a IANA assigned UDP destination port, 4790, when sending traffic to VXLAN-GPE VTEPs.¶

6.4. VXLAN-GPE and Encapsulated IP Header Fields

When encapsulating IP (including over Ethernet) packets [RFC2983] provides guidance for mapping DSCP between inner and outer IP headers. The Pipe model typically fits better Network virtualization. The DSCP value on the tunnel header is set based on a policy (which may be a fixed value, one based on the inner traffic class, or some other mechanism for grouping traffic). Some aspects of the Uniform model (which treats the inner and outer DSCP value as a single field by copying on ingress and egress) may also apply, such as the ability to remark the inner header on tunnel egress based on transit marking. However, the Uniform model is not conceptually consistent with network virtualization, which seeks to provide strong isolation between encapsulated traffic and the physical network.¶

[RFC6040] describes the mechanism for exposing ECN capabilities on IP tunnels and propagating congestion markers to the inner packets. This behavior MUST be followed for IP packets encapsulated in VXLAN-GPE.¶

Though Uniform or Pipe models could be used for TTL (or Hop Limit in case of IPv6) handling when tunneling IP packets, Pipe model is more aligned with network virtualization. [RFC2003] provides guidance on handling TTL between inner IP header and outer IP tunnels; this model is more aligned with the Pipe model and is recommended for use with VXLAN-GPE for network virtualization applications.¶

When a VXLAN-GPE router performs Ethernet encapsulation, the inner 802.1Q 3-bit priority code point (PCP) field MAY be mapped from the encapsulated frame to the DSCP codepoint of the DS field defined in [RFC2474].¶

When a VXLAN-GPE router performs Ethernet encapsulation, the inner header 802.1Q VLAN Identifier (VID) MAY be mapped to, or used to determine the VXLAN Network Identitifer (VNI) field.¶

11.1. UDP Port

UDP 4790 port has been assigned by IANA for VXLAN-GPE in the "Service Name and Transport Protocol Port Number" registry.¶

11.2. VXLAN-GPE Next Protocol

VXLAN-GPE 'Next Protocol' values are tracked by the IANA "LISP-GPE Next Protocol" registry, defined in Section 6.1 of [RFC9305] that VXLAN-GPE shares with LISP-GPE. New values are assigned under the Specification Required policy [RFC8126]. The protocols that are being assigned values do not themselves need to be IETF Standards Track protocols.¶

At the time this document is edited the IANA "LISP-GPE Next Protocol" registry specifies the following Next Protocol values:¶

11.3. VXLAN-GPE Flag and Reserved Bits

There are ten flag bits at the beginning of the VXLAN-GPE header, followed by 16 reserved bits and an 8-bit reserved field at the end of the header. New bits are assigned via Standards Action [RFC5226].¶

• Bits 0-1 - Reserve6¶

• Bits 2-3 - Version¶

• Bit 4 - Instance ID (I bit)¶

• Bit 5 - Next Protocol (P bit)¶

• Bit 6 - Reserved¶

• Bit 7 - OAM (O bit)¶

• Bit 8-23 - Reserved¶

• Bits 24-31 in the 2nd Word -- Reserved¶

Reserved bits/fields MUST be set to 0 by the sender and ignored by the receiver.¶