SD-WAN Edge and Underlay Tunnel Discovery Using BGP

The BGP mechanisms defined in this document support two types of advertisements: A BGP speaker supporting SD-WAN re-advertises routes received from client routers with the Next_HOP address set to its own IP address (due to the SD-WAN feature configuration) and includes a BGP attribute indicating the SD-WAN Hybrid Tunnel. Client routes MAY be advertised using the following AFI/SAFIs: Unicast IPv4/IPv6 (1/1, 2/1) and L3VPN IPv4/IPv6 (1/128, 2/128). The SD-WAN tunnel indication can be conveyed using either the Encapsulation Extended Community or the Tunnel Encapsulation Attribute. A BGP speaker advertises SD-WAN Underlay Routes using AFI/SAFI 1/74 or 2/74. The NEXT_HOP is set to a reachable address of the advertising SD-WAN edge node, typically its loopback address, and the UPDATE includes a Tunnel Encapsulation Attribute containing an SD-WAN Hybrid Tunnel TLV. The SD-WAN NLRI identifies the WAN port or ports, SD-WAN Color, and SD-WAN Node ID to which the advertised tunnel properties apply. The associated SD-WAN Hybrid Tunnel TLV carries the corresponding tunnel-related information, including IPsec SA properties and, optionally, NAT-related information. In this document, "Client Route" refers to the first type of advertisement, and "SD-WAN Underlay Route" refers to the second. The term "SD-WAN NLRI" refers specifically to the NLRI encoding used for an SD-WAN Underlay Route. For Client Routes, the Tunnel Encapsulation Attribute procedures of [RFC9012] apply. For SD-WAN Underlay Routes using SAFI 74, which is outside the applicability scope defined by [RFC9012], the use and processing of the Tunnel Encapsulation Attribute are defined by this document. This document does not update [RFC9012]. This section describes the SD-WAN Hybrid Tunnel, the SD-WAN NLRIs, the new sub-TLVs for SD-WAN Tunnel IPsec SA, sub-TLVs for Port attributes, the procedures for the client routes, the procedures for underlay routes, error handling, and considerations for managing SD-WAN technologies.

SD-WAN Hybrid Tunnel 25 (IANA assigned) The SD-WAN Hybrid Tunnel identifies a virtual tunnel that overlays a path across a set of underlay links between two BGP peers. These underlay links may use various technologies (e.g., MPLS, Layer 2 direct connections, or Layer 3 public Internet). The term hybrid reflects that different types of underlay links can be used simultaneously. Per [RFC9012], the following two BGP attributes that MAY encode a Tunnel Encapsulation attribute information: the Tunnel Encapsulation Attribute, and the Encapsulation Extended Community as a "barebones" tunnel identification. The encoding for the SD-WAN Hybrid Tunnel is described for both BGP attributes. The SD-WAN encoding uses the Encapsulation Extended Community defined in with the tunnel type set to 25 (IANA assigned). The NextHop Field in the BGP update indicates the tunnel egress endpoint and this field SHOULD be set to the BGP Peer Address for the SD-WAN Peer. The tunnel TLV has a type set to 25 (IANA assigned). The valid Sub-TLVs for client routes are the Color Sub-TLV (defined in ), and the following Sub-TLVs defined in sections 2.2 and 2.3 of this document: IPSec SEC ID, IPsec SA Rekey Cnt, IPsec Public Key, IPsec SA Proposal, and Simplified IPsec SA. The valid Sub-TLVs for underlay tunnels are the Tunnel Egress End Point defined in [RFC9012] and the following Sub-TLVs defined in sections 2.2 and 2.3 of this document: IPSec SEC ID, IPsec SA Rekey Cnt, Extended Port Attr, Underlay Type, IPsec Public Key, IPsec SA Proposal, and Simplified IPsec SA. For SD-WAN Underlay Routes using SAFI 74, if a Tunnel Egress Endpoint Sub-TLV is not included in the SD-WAN Hybrid Tunnel TLV, it is treated as if a Tunnel Egress Endpoint Sub-TLV with an Address Family value of 0 were included. For Client Routes, Tunnel Egress Endpoint processing follows [RFC9012]. Figure 1 summarizes this Sub-TLV support in a tabular format.

The Color Sub-TLV defined in [RFC9012] is not used by the SD-WAN procedures defined in this document. Client Routes carry the Color Extended Community, while SD-WAN Underlay Routes carry the SD-WAN-Color field in the SAFI-74 NLRI. The receiving BGP speaker correlates these values as described in Sections 2.4.1, 2.4.3, and 3.1.

The SD-WAN Hybrid Tunnel TLV and its Sub-TLVs MUST first be validated for correct encoding and applicability as specified in this section and Section 2.3. Route-specific validation procedures are specified in Section 2.4.2 for Client Routes and Section 2.5.2 for SD-WAN Underlay Routes. Error handling is specified in Section 2.6. After the SD-WAN Hybrid Tunnel TLV has been validated, the receiving BGP speaker processes it according to the applicable route procedure.

When Encapsulation Extended Community with a SD-WAN Hybrid Tunnel Type is attached to a client route, the detailed SD-WAN tunnel attributes are not included in the same BGP UPDATE message, but are advertised separately using the SD-WAN NLRI. Section 2.2 and 2.3 describe the processing. The SD-WAN NLRI is originated by the C-PE, and the BGP Next Hop is set to a reachable address of the C-PE, typically its loopback address. The remote BGP speaker uses this loopback address to associate the client route with the corresponding logical SD-WAN Hybrid Tunnel, and the SD-WAN NLRI SD-WAN Node ID and port to the underlay tunnel within the logial SD-WAN Hybrid Tunnel. This separation allows for independent advertisement rates and avoids bloating BGP UPDATE messages with the large amount of data required for IPsec SA, cryptographic keys, and related parameters. When the Tunnel Encapsulation Attribute with SD-WAN Hybrid Tunnel TLV is attached to the client route, the detailed underlay tunnel attributes, such as IPsec-related parameters, are included directly in the same BGP UPDATE as the client route. As a result, there is no need for a separate UPDATE message associated with the C-PE loopback address. However, this approach means that any changes to underlay attributes (e.g., IPsec keys or cryptographic parameters) necessitate re-advertising the client route with an updated Tunnel Encapsulation Attribute, which can increase both the frequency and size of BGP UPDATE messages.

An Edge BGP Peer using BGP SD-WAN discovery advertises an SD-WAN Underlay Route whose NLRI is encoded as specified in Section 2.2.1. The route carries a Tunnel Encapsulation Attribute containing an SD-WAN Hybrid Tunnel TLV to advertise the detailed properties associated with the public-facing WAN port or ports and their associated IPsec tunnels. The SD-WAN Underlay Route carries control-plane information describing an SD-WAN WAN port and its tunnel properties; the SD-WAN NLRI is not itself installed as a route for forwarding user traffic. The Edge BGP Peer sends this information to its designated RR via a secure transport connection. Each BGP UPDATE containing an SD-WAN Underlay Route MUST include a Tunnel Encapsulation Attribute with an SD-WAN Hybrid Tunnel TLV. If an SD-WAN Underlay Route is received without the required Tunnel Encapsulation Attribute and SD-WAN Hybrid Tunnel TLV, the route MUST be handled as Treat-as-withdraw as specified in Section 2.6.3. The SD-WAN Hybrid tunnel TLV within the Tunnel Encapsulation Attribute can include sub-TLVs for Extended Port attribute (see Section 2.3.6) or IPsec information (see Section 2.3). The IPsec information sub-TLVs include: IPsec SA ID, IPsec SA Rekey Counter, IPsec Public Key, IPsec SA Proposal, and Simplified IPsec SA.

A new NLRI SAFI (SD-WAN SAFI=74) is introduced within the MP_REACH_NLRI Path Attribute of [RFC4760] for advertising the detailed properties of SD-WAN tunnels terminated at the WAN ports of the edge nodes. The SD-WAN SAFI uses the Tunnel Encapsulation Attribute and Tunnel TLV/sub-TLV encodings defined in [RFC9012]. Because SAFI 74 is outside the AFI/SAFIs for which [RFC9012] defines applicability procedures, this document defines the use of the Tunnel Encapsulation Attribute with SAFI 74, including the associated next-hop, propagation, and validation procedures. This is a "typed" NLRI (similar to other "typed" NLRIs as described in [RFC7606]). The format is shown in figure 2. For AFI/SAFI 1/74, the MP_REACH_NLRI Next Hop Network Address field MUST contain a 4-octet IPv4 address. For AFI/SAFI 2/74, it MUST contain a 16-octet IPv6 address. The Next Hop MUST contain a reachable address of the advertising SD-WAN edge node, typically its loopback address or SD-WAN Node ID.

where: A 2-octet value that defines the encoding of the reminder of the SD-WAN the NLRI. 2 octets indicating the length of the value field in octets. This document defines the following SD-WAN Route type: For advertising the detailed properties of the SD-WAN tunnels terminated at the edge, where the transport network port can be uniquely identified by a tuple of three values (Port-Local-ID, SD-WAN-Color, SD-WAN Node ID). The SD-WAN NLRI Route Type =1 has the following encoding:

The value of the Length field for Route-Type 1 MUST be either 12 octets (when the SD-WAN Node ID is an IPv4 address) or 24 octets (when the SD-WAN Node ID is an IPv6 address). Any other value is invalid. Error handling for an invalid Length field is specified in Section 2.6.2.. SD-WAN edge node Port identifier, which is locally significant. If the SD-WAN NLRI applies to multiple WAN ports, this field is zero. identifies a group of Hybrid SD-WAN tunnels that may span multiple SD-WAN logical tunnels co-located at the same site. The BGP Peer supporting SD-WAN uses this SD-WAN-Color value to allow local policy to correlate client routes identified by the Color Extended Community to a specific group of Hybrid SD-WAN tunnels or a specific set of underlay tunnels within the Hybrid SD-WAN tunnel. If the SD-WAN-Color represents all tunnels at a site, it effectively serves as a site-level identifier. If no matching SD-WAN-Color is found, the client route is not be forwarded over any SD-WAN tunnels. However, local configuration MAY remove this restriction. This field carries the IPv4 or IPv6 address of the SD-WAN edge node (C-PE). For IPv4 SD-WAN NLRI (AFI/SAFI 1/74), this field contains a 4-octet IPv4 address representing a /32 host address. For IPv6 SD-WAN NLRI (AFI/SAFI 2/74), this field contains a 16-octet IPv6 address representing a /128 host address. The SD-WAN Node ID identifies the IP address (usually the loopback address) used by the SD-WAN edge node to advertise its tunnel attributes of a tunnel underlay route within the logical SD-WAN Hybrid logical tunnel.

Upon receiving an SD-WAN NLRI, the following validation steps are performed: The Route Type field MUST be equal to 1. An SD-WAN NLRI with an unrecognized Route Type MUST be discarded and MUST NOT be propagated, as specified for typed NLRIs in Section 5.4 of [RFC7606]. For Route type1, the Length field MUST contain a value of either 12 or 24 octets, as defined in Section 2.2.1. Any other value renders the SD-WAN NLRI malformed. Error handling is specified in Section 2.6.2. If Length = 12, the SD-WAN Node-ID field contains an IPv4 Unicast address. If Length = 24, the SD-WAN Node-ID field contains an IPv6 Unicast address. The SD-WAN Node-ID MUST be a valid unicast address. Otherwise, the NLRI must be discarded.

The Path Attributes attached to the SD-WAN NLRIs apply to the WAN-facing tunnel endpoints being advertised, not to client routes. These attributes describe properties of the WAN ports (e.g., encapsulation, transport role, or color) that may be used in establishing SD-WAN underlay tunnels between edge nodes. Client routes, which represent customer prefixes, are propagated using separate BGP NLRIs (e.g., IPv4/IPv6 unicast or L3VPN), with their own associated Path Attributes. The SD-WAN NLRI and client route NLRI are independent but may be correlated by the receiving BGP speaker for tunnel selection and service mapping.

The IPsec SA Property Sub-TLVs defined in this section specify encodings that allow BGP UPDATE messages to carry IPsec-related parameters associated with SD-WAN Hybrid Tunnels to authorized peers. BGP does not establish, negotiate, derive, or maintain IPsec SAs. BGP validation of these Sub-TLVs is limited to their encoding and syntactic validity. The creation and operation of an IPsec SA, including algorithm validation, key derivation, SA state management, rekeying, and packet protection, are performed by the IPsec implementation according to [RFC4301] and, when IKEv2 is used, [RFC7296], together with local policy. While these Sub-TLV formats could potentially be reused in other applications that require IPsec SA signaling over BGP, this document defines their semantics and behavior specifically within the SD-WAN Edge Discovery framework. If any sub-TLV is malformed, error handling MUST follow the procedure in Section 13 of . To support key rotation (e.g., updating IPsec keys or parameters), the SD-WAN NLRI (identified by Port-Local-ID, SD-WAN-Color, and SD-WAN Node ID) can be re-advertised via a BGP UPDATE message containing updated IPsec SA information. In the centrally controlled SD-WAN model described in this document, IPsec SA parameters and keying material can be distributed to authorized SD-WAN edge nodes through the RR/Controller. Therefore, peer-to-peer key negotiation between SD-WAN edge nodes is not required by this mechanism. A deployment MAY use IKEv2 or another key-management mechanism instead.

The IPsec SA ID Sub-TLV is used to reference one or more previously established IPsec SAs between SD-WAN nodes. This Sub-TLV carries one or more 32-bit Security Parameter Index (SPI) values assigned at the receiving node (i.e., the inbound SPI). When combined with the SD-WAN Node-ID (which identifies the underlay tunnel endpoint address), each SPI uniquely identifies an existing IPsec SA, consistent with the SA identification described in [RFC4301]. Multiple SPIs MAY be included within the Sub-TLV to reference multiple pre-established IPsec SAs available for the SD-WAN overlay. This enables advertisement of SA updates, key rotations, or operational state changes without resending full SA parameter sets, and allowing pairwise IPsec rekeying to proceed independently for each SA. IPsec SA ID 64 (IANA assigned)

where: IPsec SA ID (8 bits): 64(IANA Assigned). Length (8 bits): Specifies the total length in octets of the value field (not including the Type and Length fields). For the IPsec SA ID Sub-Type, the Length field MUST be equal to 2 + 4 *(number of IPsec SA Identifier fields). Reserved: Reserved for future use. MUST be set to zero on transmission and MUST be ignored on receipt. A sequence of IPsec SA Identifier fields follows the reserved field. Each IPsec SA Identifier field is 4 octets long, and identifies a pre-established IP security association. An IPsec SA ID Sub-TLV whose Length field is not equal to 2 + 4 x (number of IPsec SA Identifier fields) is malformed and is handled according to [RFC9012].

The IPsec SA Rekey Counter Sub-TLV carries rekey-related information associated with a specific IPsec Security Association (SA). The SA is identified by the 32-bit Security Parameter Index (SPI) carried in this Sub-TLV. Together with the IPsec protocol and destination address associated with the advertised tunnel endpoint, the SPI identifies the inbound IPsec SA as described in . The Rekey Counter and Nonce Data defined in this Sub-TLV are SD-WAN-specific fields. They are not IKEv2 protocol fields and do not require IKEv2 signaling. BGP carries these fields as part of the SD-WAN tunnel information but does not interpret them for route selection or BGP processing. IPsec SA Rekey Counter 67 (IANA assigned)

where: IP SA-Rekey Counter (8 bits): IPsec SA Rekey Counter Sub-TLV Type = 67 (IANA assigned). length (8 bits): Specifies the total length, in octets, of the Sub-TLV value field, excluding the Type and Length fields. The Length MUST equal 18 + Nonce Length. Reserved (16 bits): Reserved for future use. The Reserved field MUST be set to zero and MUST be ignored upon receipt. Reserved2 (8 bits): Reserved for future use. The Reserved field MUST be set to zero and MUST be ignored upon receipt. Nonce Length (16 bits): Indicates the length, in octets, of the Nonce Data. The Nonce Length MUST be between 8 and 237 octets, inclusive. A Nonce Length of at least 16 octets is RECOMMENDED. The upper bound ensures that the complete Sub-TLV value fits within the 255-octet limit imposed by the one-octet Sub-TLV Length field. I Flag: When set to 1, the I Flag indicates that the advertised information is associated with a new SA instance. When set to 0, it indicates an update associated with an existing SA instance. Flags (7 bits): Reserved for future use. These bits MUST be set to zero and MUST be ignored upon receipt. Rekey Counter (64 bits): Carries an unsigned counter associated with rekeying of the identified IPsec SA. The Rekey Counter is opaque to BGP and is passed unchanged to the SD-WAN/IPsec implementation. BGP does not use this value for route selection, freshness determination, or replay detection. SPI: Carries the 32-bit Security Parameter Index of the IPsec SA. Together with the IPsec protocol and destination address associated with the advertised tunnel endpoint, the SPI identifies the inbound IPsec SA as described in . Nonce Data: Carries an SD-WAN-specific nonce associated with the advertised IPsec SA information. The nonce can be used by the receiving SD-WAN/IPsec implementation as a freshness value when processing SA information. Generation, storage, comparison, and replay handling of the nonce are outside the scope of BGP. The Sub-TLV is malformed if the Length field is not equal to 18 + Nonce Length, or if the Nonce Length is less than 8 or greater than 237 octets. A malformed IPsec SA Rekey Counter Sub-TLV is handled according to the procedures specified in .

The IPsec Public Key Sub-TLV provides the Public Key exchange information and the life span for the Diffie-Hellman Key. The encoding is shown in the figure below:

where: IPSec-PublicKey (8 bits): Type value for Sub-TLV is 68 (IANA assigned). length (8 bits): The Length field MUST equal 10 + the Key Exchange Data length. Because the fixed fields occupy 10 octets, the Key Exchange Data MUST NOT exceed 245 octets. Key Exchange Method Group Num (16 bits): identifies the key exchange method used to compute the Key Exchange Data. Values are taken from the IANA IKEv2 "Transform Type 4 - Key Exchange Method Transform IDs" registry. Additional information on the key exchange groups is provided in Appendix B of IKEv2 [RFC7296], [RFC5114], and [RFC5903] for elliptic-curve groups. Key Exchange data: This field contains a copy of the sender's Diffie-Hellman public value. Because the RFC 9012 sub-TLV Length field is one octet, the total value carried in this IPsec Public Key Sub-TLV is limited to 255 octets. Therefore, the encoded public value, together with the other fields in this Sub-TLV, MUST fit within this limit. Elliptic-curve Diffie-Hellman groups are RECOMMENDED because their public values are smaller; for example, Groups 19, 20, and 21 use public values of 64, 96, and 132 octets, respectively, as defined in [RFC5903]. If the selected Diffie-Hellman public value cannot fit within this Sub-TLV, the public key MUST be distributed by another mechanism, such as the SD-WAN controller or management system. Duration (32 bits): a 4-octet value specifying the life span of the Diffie-Hellman key in seconds. An IPsec Public Key Sub-TLV is considered malformed if any of its fields do not conform to the encoding rules specified above. Malformed Sub-TLVs are handled according to [RFC9012].

The IPsec SA Proposal Sub-TLV is used to advertise a set of cryptographic parameters that define the proposal for establishing an IPsec SA. In the centrally controlled SD-WAN model described in this document, the participating SD-WAN edge nodes operate under coordinated administrative policy, reducing the need to advertise multiple alternative proposals for negotiation. Therefore, only one IPsec SA Proposal Sub-TLV is processed for a given SD-WAN Hybrid Tunnel TLV. IPsec SA Proposal - Indicates IPsec Transform Attributes 69 (IANA assigned) A Transform Type, which identifies the function being specified (e.g., encryption, integrity). A Transform ID, which specifies the algorithm for that function. Optional Transform Attributes, which provide additional algorithm-specific parameters when necessary. The encoding is shown below:

where: IPsec SA Proposal Sub-Type (8 bits): 69 (IANA assigned) length (8 bits): Total length of the value field in octets (not including Type and Length fields). This equals 10 + the Transform attribute length. Reserved (16 bits): reserved for future use. MUST be set to zero on transmission and MUST be ignored on receipt. Transform Attr Length (16 bits): length of the Transform Attributes field in octets. Transform Type (8 bits): The function being specified. Transform Type values are defined in [RFC7296] and IANA IKEv2 Transform Type registry. Valid types include: ENCR (1), PRF (2), INTEG (3), DH (4), and ESN (5). Reserved-2 (8 bits): Reserved for future use. MUST be set to zero when transmitted and ignored upon receipt. Received values MUST be propagated without change. Transform ID (16 bits): Identifies the algorithm for the corresponding Transform Type, as defined in [RFC7296]. Reserved-3 (16 bits): Reserved for future use. MUST be set to zero when transmitted and ignored upon receipt. Received values MUST be propagated without change. Transform Attributes: This is a sequence of Transform attribute TLVs. Each transform attribute TLV is encoded as defined in [RFC7296] Section 3.3.5. The Transform Attributes field may be omitted if no additional parameters are required for the selected algorithm.

An IPsec SA Proposal Sub-TLV is considered malformed if: The Length field value does not match the actual length (Transform Attr Length + 10). The Transform Attr Length field does not total length of all Transform attributes parsed. Any Transform Attribute TLV whose type, length or value field falls outside its valid range as specified in [RFC7296]. Malformed Sub-TLVs MUST be handled according to [RFC9012]. Additional content checks for the IPsec SA Proposal Sub-TLV are described in Section 2.4 (for client routes) and Section 2.5 (for underlay routes).

The Simplified IPsec SA Sub-TLV provides a compact way to signal IPsec SA parameters in a centrally controlled SD-WAN environment where the SD-WAN Controller or management system pre-configures the participating SD-WAN nodes with the required IPsec algorithms, keying methods, and other security parameters. Because these parameters are configured consistently across the SD-WAN domain, this Sub-TLV does not carry all of the information required for IPsec negotiation. It carries the parameters and keying material needed to install and operate the applicable SA instance. Simplified IPsec SA 70 (IANA assigned)

where: Simplified IPsec SA Sub-TLV type (70)[IANA assigned] Specifies the total length, in octets, of the Sub-TLV value field, excluding the Type and Length fields. The Length MUST equal 18 + Key 1 Length + Key 2 Length + Nonce Length. Therefore, the combined lengths of Key 1, Key 2, and Nonce MUST NOT exceed 237 octets. Reserved for future use. MUST be set to zero on transmission and MUST be ignored on receipt. SA-Type = 1 means AH, SA-Type = 2 means ESP All other SA-Type values are invalid. Mode = 1 indicates that the Tunnel mode is used. Mode = 2 indicates that the Transport mode is used. Only Mode values 1 and 2 are valid. All other modes are invalid. Identifies the cryptographic algorithm used by the advertised SA. When SA-Type = 1 (AH), the Algorithm field identifies the AH integrity algorithm using the corresponding value from the IANA Integrity Algorithm registry. When SA-Type = 2 (ESP), the Algorithm field identifies the ESP encryption algorithm using the corresponding value from the IANA Encryption Algorithm registry. Carries an unsigned counter associated with key rotation for the advertised IPsec SA. The Rekey Counter identifies the key generation associated with the advertised keying material. Interpretation of the counter and selection of the active key are performed by the SD-WAN/IPsec implementation. The Rekey Counter is opaque to BGP. Specifies the length, in octets, of the Key 1 field. The required key length is determined by the selected Algorithm and the configured IPsec security profile. Carries one generation of keying material for the advertised IPsec SA. The encoding and required length of the keying material are determined by the selected Algorithm and the configured IPsec security profile. Specifies the length, in octets, of the Key 2 field. The required key length is determined by the selected Algorithm and the configured IPsec security profile. Carries an alternate generation of keying material for the advertised IPsec SA. Key 1 and Key 2 allow keying material for a new generation to be distributed while the previous generation remains available during rekeying. Selection and retirement of the active key generation are performed by the SD-WAN/IPsec implementation and are outside the scope of BGP. Specifies the length, in octets, of the Nonce field. The Nonce is an SD-WAN-specific value. The Nonce Length MUST be at least 8 octets. A Nonce Length of at least 16 octets is RECOMMENDED. The combined Key 1, Key 2, and Nonce lengths MUST satisfy the Sub-TLV Length constraint specified above. Carries an SD-WAN-specific nonce associated with the advertised IPsec SA information. Generation and processing of the nonce are performed by the SD-WAN/IPsec implementation and are outside the scope of BGP. Specifies the lifetime of the advertised IPsec SA in seconds. A Simplified IPsec SA Sub-TLV is considered MALFORMED if any of its fields are not properly encoded, do not conform to the specified value ranges above, or contain invalid field lengths. Any MALFORMED Sub-TLV is processed according to .

The Extended Port Attribute Sub-TLV advertises NAT-related properties associated with a public Internet-facing WAN port on an SD-WAN edge node. This information enables peer SD-WAN nodes to establish secure tunnels even when one or both peers are behind NAT devices. An SD-WAN edge node may query a STUN server (Session Traversal Utilities for NAT [RFC8489]) to determine its NAT properties, including its public IP address and public port number. These properties are then advertised to peer nodes using the Extended Port Attribute Sub-TLV. In SD-WAN deployments, NAT devices may exist at one or both ends of the tunnel path. The possible deployment scenarios include: Only one SD-WAN edge node is located behind a NAT device, while its peer is directly reachable. Both SD-WAN edge nodes are behind NAT devices (symmetric or independent NATs). The external address and port assigned to an edge node may change dynamically, either due to ISP address allocation or when traversing NAT devices that use dynamic address pools. Because an SD-WAN edge node may have multiple WAN ports with independent NAT characteristics, the NAT properties are associated with individual WAN ports and are advertised independently for each port using this Sub-TLV. This per-port advertisement allows remote peers to construct appropriate NAT traversal parameters for each potential tunnel endpoint. Unlike pairwise NAT traversal mechanisms such as IKEv2 [RFC7296], in which NAT-related information is discovered between peers during tunnel establishment, the BGP-controlled SD-WAN architecture enables an SD-WAN edge node to advertise its NAT properties through the RR to authorized SD-WAN peers before individual tunnels are established. This avoids requiring the same NAT-related information to be discovered independently during the establishment of each SD-WAN tunnel and can reduce repeated parameter exchange in deployments where an SD-WAN edge establishes tunnels with many peers. Extended Port Attribute 65 (IANA assigned) The encoding is shown in the figure below:

where: Length: Specifies the total length, in octets, of the Sub-TLV value field, excluding the Type and Length fields. The Length MUST equal: 10 + Local-IP-Length + Public-IP-Length + the total encoded length of all included Extended Sub-Sub-TLVs. The Local-IP-Length is 4 octets when the I bit is 0 and 16 octets when the I bit is 1. The Public-IP-Length is 4 octets when the O bit is 0 and 16 octets when the O bit is 1. Flags (16 bits): Flags field starts with 8 bits which are reserved for future use. MUST be set to 0, and ignored upon reception. I bit (C-PE port address or Inner address scheme): If set to 0, the Local IP Address field contains a 4-octet IPv4 address. If set to 1, the Local IP Address field contains a 16-octet IPv6 address. O bit (Outer address scheme): If set to 0, the Public IP Address field contains a 4-octet IPv4 address. If set to 1, the Public IP Address field contains a 16-octet IPv6 address. R bits: reserved for future use. MUST be set to 0, and ignored upon reception. NAT Type (8 bits): an unsigned integer indicating the NAT behavior observed for this WAN port. The values are derived from the legacy NAT classification model described in RFC 8489 Section 5. The assigned values are: 1: without NAT ; 2: 1-to-1 static NAT; 3: Full Cone; 4: Restricted Cone; 5: Port Restricted Cone; 6: Symmetric; or 7: Unknown (e.g. no response from the STUN server). The NAT Type value is determined by the sender using NAT discovery procedures (e.g., STUN [RFC8489] with legacy tests [RFC8489]) or local administrative configuration. The receiver is not required to verify NAT behavior but MUST validate that the received NAT Type field is within the range 1-7. Values outside this range are considered invalid and result in the Sub-TLV being treated as malformed. Encap-Type (8 bits): An unsigned integer indicating the encapsulation type supported for this WAN port. The Encap-Type identifies the encapsulation protocol used within the IPsec payload when IPsec SA Sub-TLVs (IPsec SA ID, IPsec SA Rekey Counter, IPsec Public Key, IPsec SA Proposal, or Simplified IPsec SA) are present in the SD-WAN Hybrid Tunnel. This field is distinct from the Tunnel Type field in the BGP Tunnel Encapsulation Attribute [RFC9012]. The encapsulation types are: Encap-Type=1: GRE; Encap-Type=2: VxLAN; Notes: This document defines Encap-Type values 1 (GRE) and 2 (VXLAN). Additional values may be assigned in the future through the IANA registry. An unrecognized Encap-Type value does not by itself make the Sub-TLV malformed; however, an implementation MUST NOT use an encapsulation type that it does not support. The Encap-Type identifies the encapsulation protocol used within the IPsec payload when IPsec SA Sub-TLVs (IPsec SA ID, IPsec SA Rekey Counter, IPsec Public Key, IPsec SA Proposal, or Simplified IPsec SA) are present in the SD-WAN Hybrid Tunnel. The Extended Port Attribute Sub-TLV does not support NAT traversal scenarios involving IPv4/IPv6 translation (e.g., NAT64 or 6to4). Trans NetworkID (Transport Network ID) (8 bits): An identifier assigned by the SD-WAN Controller to indicate the transport network that this WAN port belongs to. All values from 0 to 255 are valid. RD ID: The Routing Domain ID is a globally unique identifier assigned to the routing domain associated with this WAN port. All values from 0 to 255 are valid. Some SD-WAN deployments may define multiple levels, zones, or regions that are represented as logical routing domains or transport networks. Operational policies may govern whether SD-WAN Hybrid tunnels or underlay tunnels are allowed between nodes in different logical routing domains. The definition, distribution, and enforcement of such policies are outside the scope of this document. Local IP: The local or private IP address of the WAN port. The address family and field length are determined by the I bit. If I = 0, this field contains a 4-octet IPv4 address. If I = 1, this field contains a 16-octet IPv6 address. Local Port: The port number associated with the local IP address of the WAN endpoint. Together with the Local IP address, it identifies the local endpoint of the NAT mapping. A value of 0 indicates that no port number is specified or applicable. Valid values: 0x00 - 0xFFFFFFFF. Public IP: The public IP address of the WAN port after NAT processing. The address family and field length are determined by the O bit. If O = 0, this field contains a 4-octet IPv4 address. If O = 1, this field contains a 16-octet IPv6 address. If NAT is not used, this field MUST be set to all zeros. Public Port: The port number associated with the Public IP address after NAT processing. Together with the Public IP address, it identifies the public endpoint of the NAT mapping. If NAT is not used, this field MUST be set to zero. Otherwise, the value can be 0x01 to 0xFFFFFFFF. If NAT is not used for the WAN port, both the Public IP and Public Port fields MUST be set to zero. If one field is set to zero and the other is non-zero, the Sub-TLV is considered malformed. Extended Sub-Sub-TLV: Carries additional information about the underlay networks. If the Extended Port Attribute Sub-TLV is malformed (e.g., incorrect length, invalid address format, or unrecognized NAT type), it MUST be ignored per the procedures described in [RFC9012]. Multiple Extended Port Attribute Sub-TLVs are allowed. If the informsation from multiple Extended Port Attribute Sub-TLVs is the same, the first one is processed, the rest is ignored.

One Extended Sub-Sub-TLVs is specified in this document: Underlay Network Type Sub-Sub-TLV. The Underlay Network Type Sub-Sub-TLV is an optional Sub-Sub-TLV used to advertise additional transport characteristics for the WAN port, including connection type, physical port type, and port bandwidth (e.g., LTE, DSL, Ethernet, and others). This information assists remote peers or controllers in selecting optimal underlay paths when multiple WAN ports are available. The Underlay Network Type Sub-Sub-TLV is only valid for the Tunnel SD-WAN Hybrid Tunnel TLV within the Extended Port Attribute Sub-TLV. Underlay Network Type. 1 (IANA Assigned). The encoding is shown in the figure below:

Where: Underlay Network Type (1 assigned by IANA) always 6 bytes 2-octet of reserved bits. It SHOULD be set to zero on transmission and MUST be ignored on receipt. An unsigned integer indicating the connection type for this WAN port. Only a single value is carried per instance. The following values are defined: 1 = Wired 2 = WIFI 3 = LTE 4 = 5G Values outside the range 1-4 are invalid and render the Sub-TLV malformed. An unsigned integer indicating the physical port type of the WAN interface. Only a single value is carried per instance. The following values are defined: 1 = Ethernet 2 = Fiber Cable 3 = Coax Cable 4 = Cellular This document defines Connection Type values 1 through 4. Additional values may be defined by future specifications and assigned through the IANA registry. Until then, values other than those defined by this document are unsupported. An implementation receiving an unsupported Connection Type value MUST NOT use that value for tunnel selection or establishment. An unsigned 16-bit integer representing the port speed in megabits per second (Mbps). For example, a value of 1000 represents a port speed of 1000 Mbps (1 Gbps). The valid range is 1-65535. A Port Speed value of 0 is invalid and renders the Sub-TLV malformed. The Underlay Network Type Sub-Sub-TLV is MALFORMED if its encoding or length is invalid. This document defines the valid Connection Type and Port Type values listed above. Additional values may be defined by future specifications and assigned through the corresponding IANA registries. Until such values are defined, other values are invalid. If a MALFORMED Sub-Sub-TLV is contained in the Extended Port Attribute Sub-TLV, then the Extended Port Attribute Sub-TLV is also MALFORMED. Per , a MALFORMED Sub-TLV is ignored.

Client routes with NLRI of AFI/SAFI IPv4 Unicast (1/1), IPv6 (2/1), L3VPN v4 Unicast (1/128), and IPv6 L3VPN (2/128) that use the SD-WAN Hybrid Tunnel Type can be advertised using one of two mechanisms: In this approach, the client route is advertised using Encapsulation Extended Community with the SD-WAN Hybrid tunnel type. The detailed tunnel properties, such as IPsec SAs, WAN port attributes, NAT properties, and other parameters, are advertised separately via BGP UPDATE messages using the SD-WAN SAFI. The SD-WAN Node ID, carried as the NextHop in client route advertisements and as the SD-WAN Node ID in SD-WAN SAFI underlay route advertisements, enables receiving BGP nodes to associate client routes with the correct underlay tunnels. Alternatively, client routes UPDATEs can include all tunnel-related information directly in the same BGP UPDATE using the Tunnel Encapsulation Attribute. The SD-WAN Hybrid Tunnel TLV specifies the outer tunnel through which the underlay tunnel identified by SD-WAN Node ID passes. This outer tunnel is identified by the Tunnel Egress Endpoint Sub-TLV. When the BGP Next Hop is used as the tunnel endpoint, the Tunnel Egress Endpoint Sub-TLV is encoded with Address Family 0 as specified in [RFC9012]. The Tunnel Encapsulation Attribute based approach, which includes all tunnel attributes within route advertisement, can simplify the processing at the receiving nodes. However, it may lead to significant BGP attribute overhead, particularly when multiple IPsec SAs are eligible to carry the same client route. In contrast, the Encapsulation Extended Community approach (the "barebones" method defined in [RFC9012]) combined with SD-WAN SAFI separates tunnel attributes from route Updates, allows tunnel properties to be reused across multiple client routes. The SD-WAN Secure Links topology is supported using unicast IPv4 and IPv6 routes. L3VPN topologies, on the other hand, support the formation of Secure SD-WAN L3VPNs as described in [SD-WAN-BGP-USAGE] and MEF specifications [MEF 70.1] and [MEF 70.2].

When client routes are advertised using the Encapsulation Extended Community with the SD-WAN Hybrid Tunnel Type, as specified in [RFC9012], the Encapsulation Extended Community identifies the tunnel type, and the NextHop field in the BGP UPDATE serves as the Tunnel Egress Endpoint. Validation of the Tunnel Egress Endpoint follows the procedures defined in Sections 13 of [RFC9012], as applied to the NextHop. The Color Extended Community is used to associate a client route with its eligible underlay tunnels. The Color value in the client route identifies the set of underlay tunnels, previously advertised with the same Color via SD-WAN SAFI, that may be used to transport the traffic. This enables SD-WAN ingress nodes or controllers to apply path selection policies based on performance, cost, or service requirements.

When client routes are advertised using the Tunnel Encapsulation Attribute with the SD-WAN Hybrid Tunnel Type, the following procedures apply for validating the BGP UPDATE message: For Client Routes, the SD-WAN Hybrid Tunnel TLV and its Tunnel Egress Endpoint Sub-TLV are validated and handled according to [RFC9012]. MALFORMED and unrecognized Sub-TLVs are handled according to [RFC9012]. The SD-WAN Hybrid Tunnel TLV processes only the first instance of each Sub-TLV, except for the IPsec SA ID Sub-TLV. Multiple IPsec SA ID Sub-TLVs MAY be processed if their IPsec SA Identifiers are unique. If a subsequent IPsec SA ID Sub-TLV contains an identifier already advertised in an earlier instance, that Sub-TLV is ignored and not propagated. Per [RFC9012] validation procedures for a Tunnel Egress Endpoint. Note: The Tunnel Egress Endpoint represents the outer tunnel through which the underlay tunnels specified by the SD-WAN NLRI operate. The tunnel link MAY be active or inactive. Multiple unique SD-WAN Hybrid Tunnel TLVs MAY be included in the Tunnel Encapsulation Attribute, but duplicate SD-WAN Hybrid Tunnel TLVs should be ignored silently. Optionally, duplicate SD-WAN Hybrid Tunnel TLVs MAY be logged. Local policy is run to validate routes. The Next Hop MUST be be reachable via the tunnel.

When a client route is advertised with the Encapsulation Extended Community that identifies the SD-WAN Hybrid Tunnel Type, the route may also include a Color Extended Community (Color-EC). This combination allows the route to be carried over multiple underlay tunnels that were previously advertised, each with the same Color value. The Color-EC serves as a correlation mechanism: all underlay tunnels that have been advertised (via SD-WAN SAFI) with the same Color value are considered eligible to carry the traffic for the client route. This approach supports flexible path selection and tunnel diversity while avoiding the need to enumerate each tunnel per route. This model is especially useful when: A site has multiple available IPsec tunnels or WAN links. A centralized controller or ingress SD-WAN edge node must select the optimal tunnel for forwarding based on performance, policy, or service constraints. The tunnel attributes, including IPsec parameters, NAT traversal info, and WAN port properties, are conveyed separately via SD-WAN SAFI updates. This keeps client route updates minimal, allowing multiple routes to reference the same tunnel attributes by using the Color-EC.

In a BGP-controlled SD-WAN network, the VPN ID distinguishes client VPNs and ensures route separation. It is conveyed in client route UPDATEs as follows: For IPv4/IPv6 Unicast (AFI/SAFI = 1/1 or 2/1), client routes received from different client-facing ports may be configured to belong to different VPNs when traversing the SD-WAN network. The Route Target Extended Community [RFC4360] SHOULD be included in the BGP advertisement to identify the VPN associated with each client route. Remote SD-WAN edge nodes use the Route Target to associate the received client route with the corresponding VPN forwarding context. If all client routes belong to a single VPN, the Route Target MAY be omitted. For VPN-IPv4/VPN-IPv6 routes (AFI/SAFI = 1/128 or 2/128), the Route Distinguisher is part of the BGP NLRI and distinguishes otherwise identical prefixes belonging to different VPNs. The Route Target controls VPN membership and route import/export policy. Overlapping prefixes belonging to different VPNs therefore use VPN-IPv4/VPN-IPv6 routes with distinct Route Distinguishers.

In the data plane, client traffic belonging to different VPNs MUST remain distinguishable while traversing the SD-WAN network. The method used to carry the VPN identifier depends on the encapsulation: For MPLS segments, an MPLS label is used to distinguish traffic belonging to different VPNs according to the applicable MPLS VPN procedures. For IPsec segments, the VPN identifier is carried within the encapsulation protected by IPsec. For GRE encapsulation, the GRE Key field is used to identify the VPN. For VXLAN encapsulation, the VNI (Virtual Network Identifier) is used to identify the VPN.

Underlay tunnel routes in a BGP-controlled SD-WAN network are advertised using the SD-WAN SAFI, with the Tunnel Encapsulation Attribute carrying a SD-WAN Hybrid Tunnel TLV. The Tunnel Egress End Point Sub-TLV (assumed or sent) indicates the other tunnel through which these underlay tunnels operate. Remote nodes use the SD-WAN information carried in the SD-WAN SAFI, together with the applicable Color and local SD-WAN policy, to associate Client Routes with the tunnel attributes advertised by the corresponding SD-WAN edge nodes. The SD-WAN Node ID identifies an individual SD-WAN edge node, while the SD-WAN-Color identifies a group of eligible SD-WAN tunnels. Tunnels associated with the same SD-WAN-Color MAY terminate on different WAN ports or different SD-WAN edge nodes. This enables multiple SD-WAN edge nodes to provide connectivity for the same Color group, subject to local policy. The BGP Next Hop identifies a reachable address of the advertising SD-WAN edge node and is not required to equal the SD-WAN Node ID. Normal BGP best-path selection applies when multiple paths for the same SD-WAN NLRI are received; the SD-WAN Hybrid Tunnel TLV and its Sub-TLVs do not participate in best-path selection. The RR reflects authorized SD-WAN Underlay Routes within the SD-WAN administrative domain according to [RFC4456].

The SD-WAN Hybrid NLRI MUST be accompanied by the Tunnel Encapsulation Attribute, and MUST NOT be accompanied by an Encapsulation Extended Community.

The procedure for processing underlay routes follows the following steps: A SD-WAN Hybrid Tunnel TLV is well-formed using only Sub-TLVs valid for association with the underlay Route (see section 2.1). The IPsec SA ID sub-TLVs MAY have multiple instances of the sub-TLV if the IPsec SA Identifiers are unique, but if the IPsec SA Identifiers are not unique the second sub-TLV is ignored and not propagated. If multiple Extended Port Sub-TLVs exist, the TLVs must be validated in step 4. For all other valid Sub-TLVs (see section 2.1), only the first instance of a Sub-TLV is processed; subsequent ones are ignored. The Tunnel Egress Endpoint validation is done per [RFC9012] rules either on the Tunnel Egress Endpoint Sub-TLV received in the UPDATE or an "assumed" Tunnel Egress Endpoint if no Tunnel Egress Endpoint Sub-TLV exists in the TLV (see section 2.1). Practically, the outer tunnel group either identifies a specific WAN interface or (in the case of the "assumed" Tunnel Egerss Endpoint) the remote SD-WAN edge node at which the outer SD-WAN Hybrid Tunnel terminates. As described in Section 2.3.6, each Extended Port Attribute sub-TLV describes the properties of a single WAN port. Therefore, multiple Extended Port sub-TLVs may be present when the SD-WAN edge node has multiple WAN ports. Each Sub-TLV MUST be validated for correct encoding and field values according to Section 2.3.6. If an Extended Port Attribute Sub-TLV is malformed, it MUST be handled according to Section 13 of [RFC9012] and Section 2.6.1 of this document. Each typed NLRI in the SD-WAN Underlay MUST be well-formed, meaning it conforms to the structure defined in Section 2.2.1, including correct field lengths and ordering. A MALFORMED NLRI MUST be discarded; implementations MAY log an error. The MP_REACH_NLRI Next Hop MUST satisfy the encoding requirements specified in Section 2.2.1 and identify a reachable address of the advertising SD-WAN edge node. The SD-WAN Underlay Route carries tunnel-control information and is not installed as a forwarding route for user traffic.

As specified in Section 2.2.1, a Route Type 1 NLRI includes the tuple (Port-Local-ID, SD-WAN-Color, SD-WAN Node ID). The Port-Local-ID field MAY be set to zero to indicate that the NLRI applies to all WAN ports on the identified SD-WAN node, effectively representing tunnel attributes at the node level rather than a specific port. When Port-Local-ID = 0, the receiving BGP speaker SHOULD apply local policy to determine how to associate client routes with underlay tunnels. This local policy may prefer tunnels from specific SD-WAN nodes, or choose among SD-WAN Colors based on administrative preference, link type, path performance, or service-level objectives. The exact selection logic is implementation-specific. It is valid for multiple such node-level NLRIs to be received, each advertising different SD-WAN Colors for the same node. For example, the following three NLRIs may be received (within one or more UPDATE messages): Port-Local-ID (0), SD-WAN-Color (10), SD-WAN Node ID (192.0.2.2), Port-Local-ID (0), SD-WAN-Color (20), SD-WAN Node ID (192.0.2.2), and Port-Local-ID (0), SD-WAN-Color (30), SD-WAN Node ID (192.0.2.2). These indicate that node 192.0.2.2 supports multiple tunnel groups, each classified by a different SD-WAN Color. For example, these Colors may correspond to service tiers such as gold, silver, and bronze. The SD-WAN-Color field is used to correlate underlay tunnels with client routes that carry a matching Color Extended Community. If no match is found, the client route may not be forwarded over any SD-WAN tunnel.

An underlay tunnel passes through only one SD-WAN Hybrid Tunnel. Therefore, if there are more than one SD-WAN Hybrid Tunnel TLV within a single Tunnel Encapsulation Attribute, the first is processed and the subsequent SD-WAN Hybrid Tunnel TLVs are ignored.

This section specifies the error-handling procedures for validation failures identified by the procedures in Sections 2.4 and 2.5. It covers Tunnel Encapsulation signaling and SD-WAN Underlay Route errors. Section 2.4 specifies the procedures for Client Routes, and Section 2.5 specifies the procedures for SD-WAN Underlay Routes.

For Client Routes, error handling for the Tunnel Encapsulation Attribute follows Section 13 of [RFC9012]. For SD-WAN Underlay Routes using SAFI 74, error handling for the Tunnel Encapsulation Attribute and its Sub-TLVs is defined by this document. Sub-TLVs that are not applicable to SAFI 74 MUST be ignored and MAY be removed when the route is propagated. A malformed Sub-TLV within an SD-WAN Hybrid Tunnel TLV MUST be handled according to Section 13 of [RFC9012]. Unless explicitly specified otherwise in this document, the malformed Sub-TLV is treated as an unrecognized Sub-TLV and ignored; it does not cause the entire SD-WAN Hybrid Tunnel TLV or the associated route to be withdrawn. For Client Routes carrying a Tunnel Encapsulation Attribute with an SD-WAN Hybrid Tunnel TLV, the IPsec Sub-TLVs (IPsec SA ID, IPsec SA Rekey Counter, IPsec Public Key, IPsec SA Proposal, and Simplified IPsec SA) MAY be included. Malformed Sub-TLVs are handled according to [RFC9012]. If multiple instances of the IPsec Rekey Counter, IPsec Public Key, IPsec Proposal, and Simplified IPsec are received within a SD-WAN Hybrid Tunnel TLV , only the first is processed. The second instance is ignored and not propagated. The IPsec SA ID MAY have multiple copies, but the IPsec SA Identifiers sent in the second sub-TLV MUST be different than any in the first IPsec SA ID sub-TLV. If multiple instances of the Extended Port sub-TLV are received, the local policy MUST determine which is to be used.

The SD-WAN NLRI [AFI/SAFI = 1/74 or 2/74] utilizes a Route Type field to describe the format of the NLRI. This specification defines Route Type 1. An NLRI with an unsupported Route Type MUST be discarded and MUST NOT be propagated to other peers. The implementation MAY log an error upon reception of an unsupported Route Type. If a recognized SD-WAN NLRI is malformed but its Length field still allows the receiver to determine where that NLRI ends and the next NLRI begins, the affected NLRI MUST be handled as Treat-as-withdraw according to [RFC7606]. Error handling for other malformed SD-WAN NLRIs follows the BGP UPDATE error-handling procedures specified in [RFC7606]. If the MP_REACH_NLRI Next Hop field for an SD-WAN Underlay Route has an invalid encoding or length such that the NLRI field cannot be reliably located, the error MUST be handled according to the applicable session-reset or AFI/SAFI-disable procedures specified in [RFC7606]. Local configuration and policy MUST carefully constrain the SD-WAN-NLRI, tunnels, and IPsec security associations to create a "walled garden".

The SD-WAN NLRI (AFI/SAFI=1/74 or 2/74) MUST be paired with a Tunnel Encapsulation Attribute containing an SD-WAN Hybrid Tunnel TLV. If the SD-WAN NLRI exists in a BGP UPDATE without a Tunnel Encapsulation Attribute containing an SD-WAN Hybrid Tunnel TLV, the NLRI is considered malformed and the Treat-as-withdraw approach specified in [RFC7606] MUST be used. TThe SD-WAN NLRI MUST NOT be paired with an Encapsulation Extended Community. If an SD-WAN NLRI is paired with an Encapsulation Extended Community rather than a Tunnel Encapsulation Attribute, the SD-WAN NLRI is considered malformed and the Treat-as-withdraw approach specified in [RFC7606] MUST be used.