LISP Generic Protocol Extension

The LISP Data-Plane is defined in . It specifies an encapsulation format that carries IPv4 or IPv6 packets (henceforth jointly referred to as IP) in a LISP header and outer UDP/IP transport. The LISP Data-Plane header does not specify the protocol being encapsulated and therefore is currently limited to encapsulating only IP packet payloads. Other protocols, most notably Virtual eXtensible Local Area Network (VXLAN) (which defines a similar header format to LISP), are used to encapsulate Layer-2 (L2) protocols such as Ethernet. This document defines an extension for the LISP header, as defined in , to indicate the inner protocol, enabling the encapsulation of Ethernet, IP or any other desired protocol all the while ensuring compatibility with existing LISP deployments. A flag in the LISP header, called the P-bit, is used to signal the presence of the 8-bit Next Protocol field. The Next Protocol field, when present, uses 8 bits of the field allocated to the echo-noncing and map-versioning features. The two features are still available, albeit with a reduced length of Nonce and Map-Version. LISP-GPE MAY also be used to extend the LISP Data-Plane header, that has allocated all by defining a Next Protocol "shim" header that implements new data plane functions not supported in the LISP header. As an example, the use of the Network Service Header (NSH) with LISP-GPE, can be considered an extension to add support in the Data-Plane for Network Service Chaining functionalities.

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here.

This document uses terms already defined in .

As described in , the LISP header has no protocol identifier that indicates the type of payload being carried. Because of this, LISP is limited to carrying IP payloads. The LISP header contains a series of flags (some defined, some reserved), a Nonce/Map-version field and an instance ID/Locator-status-bit field. The flags provide flexibility to define how the various fields are encoded. Notably, Flag bit 5 is the last reserved bit in the LISP header.

This document defines two changes to the LISP header in order to support multi-protocol encapsulation: the introduction of the P-bit and the definition of a Next Protocol field. This is shown in and described below.

Flag bit 5 is defined as the Next Protocol bit. If the P-bit is clear (0) the LISP header conforms to the definition in . The P-bit is set to 1 to indicate the presence of the 8 bit Next Protocol field. In , LISP uses the lower 24 bits of the first word for a nonce, an echo-nonce, or to support map- versioning. These are all optional capabilities that are indicated in the LISP header by setting the N, E, and V bits respectively. When the P-bit and the N-bit are set to 1, the Nonce field is the middle 16 bits (i.e., encoded in 16 bits, not 24 bits). Note that the E-bit only has meaning when the N-bit is set. When the P-bit and the V-bit are set to 1, the Version fields use the middle 16 bits: the Source Map-Version uses the high-order 8 bits, and the Dest Map-Version uses the low-order 8 bits. When the P-bit is set to 1 and the N-bit and the V-bit are both 0, the middle 16-bits MUST be set to 0 on transmission and ignored on receipt. The encoding of the Nonce field in LISP-GPE, compared with the one used in for the LISP data plane encapsulation, reduces the length of the nonce from 24 to 16 bits. As per , Ingress Tunnel Routers (ITRs) are required to generate different nonces when sending to different Routing Locators (RLOCs), but the same nonce can be used for a period of time when encapsulating to the same Egress Tunnel Router (ETR). The use of 16 bits nonces still allows an ITR to determine to and from reachability for up to 64k RLOCs at the same time. Similarly, the encoding of the Source and Dest Map-Version fields, compared with , is reduced from 12 to 8 bits. This still allows to associate 256 different versions to each Endpoint Identifier to Routing Locator (EID-to-RLOC) mapping to inform commmunicating ITRs and ETRs about modifications of the mapping. The lower 8 bits of the first 32-bit word are used to carry a Next Protocol. This Next Protocol field contains the protocol of the encapsulated payload packet. This document defines the following Next Protocol values: IPv4 IPv6 Ethernet Network Service Header (NSH) The values are tracked in an IANA registry as described in .

To ensure that protocols that are encapsulated in LISP-GPE will work well from a transport interaction perspective, the specification of a new encapsulated payload MUST contain an analysis of how LISP-GPE SHOULD deal with outer UDP Checksum, DSCP mapping, and Explicit Congestion Notification (ECN) bits whenever they apply to the new encapsulated payload. For IP payloads, section 5.3 of specifies how to handle UDP Checksums encouraging implementors to consider UDP checksum usage guidelines in section 3.4 of when it is desirable to protect UDP and LISP headers against corruption. Each new encapsulated payloads, when registered with LISP-GPE, MUST be accompanied by a similar analysis. Encapsulated payloads may have a priority field that may or may not be mapped to the DSCP field of the outer IP header (part of Type of Service in IPv4 or Traffic Class in IPv6). Such new encapsulated payloads, when registered with LISP-GPE, MUST be accompanied by an analysis similar to the one performed in Section 3.1.1 of this document for Ethernet payloads. Encapsulated payloads may have Explicit Congestion Notification mechanisms that may or may not be mapped to the outer IP header ECN field. Such new encapsulated payolads, when registered with LISP-GPE, MUST be accompanied by a set of guidelines derived from . The rest of this section specifies payload specific transport interactions considerations for the two new LISP-GPE encapsulated payloads specified in this document: Ethernet and NSH.

The UDP Checksum considerations specified in section 5.3 of apply to Ethernet Encapsulated Payloads. Implementors are encouraged to consider the UDP checksum usage guidelines in section 3.4 of when it is desirable to protect UDP, LISP and Ethernet headers against corruption. When a LISP-GPE router performs Ethernet encapsulation, the inner 802.1Q priority code point (PCP) field MAY be mapped from the encapsulated frame to the Type of Service field in the outer IPv4 header, or in the case of IPv6 the 'Traffic Class' field. When a LISP-GPE router performs Ethernet encapsulation, the inner header 802.1Q VLAN Identifier (VID) MAY be mapped to, or used to determine the LISP Instance IDentifier (IID) field.

The UDP Checksum considerations specified in section 5.3 of apply to NSH Encapsulated Payloads. Implementors are encouraged to consider the UDP checksum usage guidelines in section 3.4 of when it is desirable to protect UDP, LISP, and NSH headers against corruption. When a LISP-GPE router performs an NSH encapsulation, DSCP and ECN values MAY be mapped as specified for the Next Protocol encapsulated by NSH (namely IPv4, IPv6 and Ethernet).

LISP-GPE uses the same UDP destination port (4341) allocated to LISP. The next Section describes a method to determine the Data-Plane capabilities of a LISP ETR, based on the use of the "Multiple Data-Planes" LISP Canonical Address Format (LCAF) type defined in . Other mechanisms can be used, including static ETR/ITR (xTR) configuration, but are out of the scope of this document. When encapsulating IP packets to a non LISP-GPE capable router the P-bit MUST be set to 0. That is, the encapsulation format defined in this document MUST NOT be sent to a router that has not indicated that it supports this specification because such a router would ignore the P-bit (as described in ) and so would misinterpret the other LISP header fields possibly causing significant errors. A LISP-GPE router MUST NOT encapsulate non-IP packets (that have the P-bit set to 1) to a non-LISP-GPE capable router.

LISP Canonical Address Format (LCAF) defines the "Multiple Data-Planes" LCAF type, that can be included by an ETR in a Map-Reply to encode the encapsulation formats supported by a given RLOC. In this way an ITR can be made aware of the capability to support LISP-GPE, as well as other encapsulations, on a given RLOC of that ETR. The 3rd 32-bit word of the "Multiple Data-Planes" LCAF type, as defined in , is a bitmap whose bits are set to one (1) to represent support for each Data-Plane encapsulation. The values are tracked in an IANA registry as described in . This document defines bit 24 in the third 32-bit word of the "Multiple Data-Planes" LCAF as: The RLOCs listed in the Address Family Identifier (AFI) encoded addresses in the next longword can accept LISP-GPE (Generic Protocol Extension) encapsulation using destination UDP port 4341

IANA is requested to set up a registry of LISP-GPE "Next Protocol". These are 8-bit values. Next Protocol values in the table below are defined in this document. New values are assigned via Standards Action . The protocols that are being assigned values do not themselves need to be IETF standards track protocols. Next Protocol Description Reference 0 Reserved This Document 1 IPv4 This Document 2 IPv6 This Document 3 Ethernet This Document 4 NSH This Document 5..255 Unassigned

IANA is requested to set up a registry of "Multiple Data-Planes Encapsulation Bitmap" to identify the encapsulations supported by an ETR in the Multiple Data-Planes LCAF Type defined in . The bitmap is the 3rd 32-bit word of the Multiple Data-Planes LCAF type. Each bit of the bitmap represents a Data-Plane Encapsulation. New values are assigned via Standards Action . Bits 0-23 are unassigned. This document assigns bit 24 (g-bit) to LISP-GPE. Bits 25-31 are assigned in ). Bit Position Bit Name Assigned to Reference 0-23 Unassigned 24 g LISP Generic Protocol Extension (LISP-GPE) This Document 25 U Generic UDP Encapsulation (GUE) 26 G Generic Network Virtualization Encapsulation (GENEVE) 27 N Network Virtualization - Generic Routing Encapsulation (NV-GRE) 28 v VXLAN Generic Protocol Extension (VXLAN-GPE) 29 V Virtual eXtensible Local Area Network (VXLAN) 30 l Layer 2 LISP (LISP-L2) 31 L Locator/ID Separation Protocol (LISP)

LISP-GPE security considerations are similar to the LISP security considerations and mitigation techniques documented in . The Echo Nonce Algorithm described in relies on the nonce to detect reachability from ITR to ETR. In LISP-GPE the use of a 16-bit nonce, compared with the 24-bit nonce used in LISP, increases the probability of an off-path attacker to correctly guess the nonce and force the ITR to believe that a non-reachable RLOC is reachable. However, the use of common anti-spoofing mechanisms such as uRPF prevents this form of attack. LISP-GPE, as many encapsulations that use optional extensions, is subject to on-path adversaries that by manipulating the g-Bit and the packet itself can remove part of the payload. Typical integrity protection mechanisms (such as IPsec) SHOULD be used in combination with LISP-GPE by those protocol extensions that want to protect from on-path attackers. With LISP-GPE, issues such as data-plane spoofing, flooding, and traffic redirection may depend on the particular protocol payload encapsulated.

A special thank you goes to Dino Farinacci for his guidance and detailed review. This Workking Group (WG) document originated as draft-lewis-lisp-gpe; the following are its coauthors and contributors along with their respective affiliations at the time of WG adoption. The editor of this document would like to thank and recognize them and their contributions. These coauthors and contributors provided invaluable concepts and content for this document's creation. Darrel Lewis, Cisco Systems, Inc. Fabio Maino, Cisco Systems, Inc. Paul Quinn, Cisco Systems, Inc. Michael Smith, Cisco Systems, Inc. Navindra Yadav, Cisco Systems, Inc. Larry Kreeger John Lemon, Broadcom Puneet Agarwal, Innovium