Network Working Group E. Crabbe, Ed. Internet-Draft Intended status: Standard Track L. Yong, Ed. Huawei USA X. Xu, Ed. Huawei Technologies Expires: April 2015 October 27, 2014 Generic UDP Encapsulation for IP Tunneling draft-ietf-tsvwg-gre-in-udp-encap-03 Abstract This document describes a method of encapsulating arbitrary protocols within GRE and UDP headers. In this encapsulation, the source UDP port may be used as an entropy field for purposes of load balancing while the payload protocol may be identified by the GRE Protocol Type. Status of This Document This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on April 27, 2015. Copyright Notice Copyright (c) 2014 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with Crabbe, el al. [Page 1] Internet-Draft Generic UDP Encapsulation for IP Tunneling October 2014 respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction...................................................3 1.1. Applicability Statement...................................3 2. Terminology....................................................4 2.1. Requirements Language.....................................4 3. Procedures.....................................................4 3.1. UDP checksum usage with IPv6..............................5 3.2. Middlebox Considerations for IPv6 UDP Zero Checksums......7 3.3. GRE-in-UDP Encapsulation Format...........................8 4. Encapsulation Considerations..................................10 5. Congestion Considerations.....................................11 6. Backward Compatibility........................................13 7. IANA Considerations...........................................13 8. Security Considerations.......................................13 8.1. Vulnerability............................................13 9. Acknowledgements..............................................14 10. Contributors.................................................14 11. References...................................................16 11.1. Normative References....................................16 11.2. Informative References..................................16 12. Authors' Addresses...........................................17 Crabbe, et al. [Page 2] Internet-Draft Generic UDP Encapsulation for IP Tunneling October 2014 1. Introduction Load balancing, or more specifically, statistical multiplexing of traffic using Equal Cost Multi-Path (ECMP) and/or Link Aggregation Groups (LAGs) in IP networks is a widely used technique for creating higher capacity networks out of lower capacity links. Most existing routers in IP networks are already capable of distributing IP traffic flows over ECMP paths and/or LAGs on the basis of a hash function performed on flow invariant fields in IP packet headers and their payload protocol headers. Specifically, when the IP payload is a User Datagram Protocol (UDP)[RFC0768] or Transmission Control Protocol (TCP) packet, router hash functions frequently operate on the five-tuple of the source IP address, the destination IP address, the source port, the destination port, and the protocol/next-header Several tunneling techniques are in common use in IP networks, such as Generic Routing Encapsulation (GRE) [RFC2784], MPLS [RFC4023] and L2TPv3 [RFC3931]. GRE is an increasingly popular encapsulation choice, especially in environments where MPLS is unavailable or unnecessary. Unfortunately, use of common GRE endpoints may reduce the entropy available for use in load balancing, especially in environments where the GRE Key field [RFC2890] is not readily available for use as entropy in forwarding decisions. This document defines a generic GRE-in-UDP encapsulation for tunneling arbitrary network protocol payloads across an IP network environment where ECMP or LAGs are used. The GRE header provides payload protocol de-multiplexing by way of it's protocol type field [RFC2784] while the UDP header provides additional entropy by way of it's source port. This encapsulation method requires no changes to the transit IP network. Hash functions in most existing IP routers may utilize and benefit from the use of a GRE-in-UDP tunnel is without needing any change or upgrade to their ECMP implementation. The encapsulation mechanism is applicable to a variety of IP networks including Data Center and wide area networks. 1.1. Applicability Statement It is recommended to use GRE-in-UDP encapsulation within a Service Provider (SP) network and/or DC network where the congestion control is not a concern. However the encapsulation can apply to ISP networks and/or Internet. Some environments request GRE-in-UDP tunnel to run more functions than others. Crabbe, et al. [Page 3] Internet-Draft Generic UDP Encapsulation for IP Tunneling October 2014 GRE-in-UDP encapsulation may be used to tunnel the tunneled traffic, i.e. tunnel-in-tunnel. The tunneled traffic may use GRE-in-UDP or other tunnel encapsulation. In this case, GRE-in-UDP tunnel end points treat other tunnel endpoints as of the end hosts for the traffic and do not differentiate such end hosts from other end hosts. The use case and applicability for a GRE-in-UDP tunnel egress and stacked tunnel egress terminate on the same IP address is for further study. 2. Terminology The terms defined in [RFC768] are used in this document. 2.1. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. 3. Procedures When a tunnel ingress device conforming to this document receives a packet, the ingress MUST encapsulate the packet in UDP and GRE headers and set the destination port of the UDP header to [TBD] Section 6. The ingress device must also insert the payload protocol type in the GRE Protocol Type field. The ingress device SHOULD set the UDP source port based on flow invariant fields from the payload header. In the case that ingress is unable to get the flow entropy from the payload header, it should set a randomly selected constant value for UDP source port to avoid payload packet flow reordering. The value, for example, may be simply a result of boot-up time. How a tunnel ingress generates entropy from the payload is outside the scope of this document. The tunnel ingress MUST encode its own IP address as the source IP address and the egress tunnel endpoint IP address. The TTL field in the IP header must be set to a value appropriate for delivery of the encapsulated packet to the tunnel egress endpoint. When the tunnel egress receives a packet, it must remove the outer UDP and GRE headers. Section 5 describes the error handling when this entity is not instantiated at the tunnel egress. For IPv4 UDP encapsulation, this field is RECOMMENDED to be set to zero because the IPv4 header includes a checksum, and use of the UDP checksum is optional with IPv4, unless checksum protection of tunneled payload is important, see Section 6. Crabbe, et al. [Page 4] Internet-Draft Generic UDP Encapsulation for IP Tunneling October 2014 For IPv6 UDP encapsulation, the IPv6 header does not include a checksum, so this field MUST contain a UDP checksum that MUST be used as specified in [RFC0768] and [RFC2460] unless one of the exceptions that allows use of UDP zero-checksum mode (as specified in [RFC6935]) applies. See Section 3.1 for specification of these exceptions and additional requirements that apply when UDP zero- checksum mode is used for GRE-in-UDP traffic over IPv6.The tunnel ingress may set the GRE Key Present, Sequence Number Present, and Checksum Present bits and associated fields in the GRE header defined by [RFC2784] and [RFC2890]. 3.1. UDP checksum usage with IPv6 When UDP is used over IPv6, the UDP checksum is relied upon to protect the IPv6 header from corruption, and MUST be used unless the requirements in [RFC 6935] and [RFC 6936] for use of UDP zero- checksum mode with a tunnel protocol are satisfied. Therefore, the UDP checksum MUST be implemented and MUST be used in accordance with [RFC0768] and [RFC2460] for GRE in UDP traffic over IPv6 unless one of the following exceptions applies and the additional requirements stated below are complied with. In addition, use of the UDP checksum with IPv6 MUST be the default configuration of all GRE-in-UDP implementations. There are two exceptions that allow use of UDP zero-checksum mode for IPv6 with GRE-in-UDP, subject to the additional requirements stated below in this section. The two exceptions are: o Use of GRE-in-UDP within a single service provider that utilizes careful provisioning (e.g., rate limiting at the entries of the network while over-provisioning network capacity) to ensure against congestion and that actively monitors encapsulated traffic for errors; or o Use of GRE-in-UDP within a limited number of service providers who closely cooperate in order to jointly provide this same careful provisioning and monitoring. As such, for IPv6, the UDP checksum for GRE-in-UDP MUST be used as specified in [RFC0768] and [RFC2460] over the general Internet, and over non-cooperating ISPs, even if each non-cooperating ISP independently satisfies the first exception for UDP zero-checksum mode usage with GRE-in-UDP over IPv6 within the ISP's own network. Section 5 of RFC6936 [RFC6936] specifies the additional requirements that implementation of UDP zero-checksum over IPv6 MUST compliant Crabbe, et al. [Page 5] Internet-Draft Generic UDP Encapsulation for IP Tunneling October 2014 with. To compliant with it, the following additional requirements apply to GRE-in-UDP implementation and use of UDP zero-checksum mode over IPv6: a. A GRE-in-UDP implementation MUST comply with all requirements specified in Section 4 of [RFC6936] and with requirement 1 specified in Section 5 of [RFC6936]. b. A GRE-in-UDP receiver MUST check that the source and destination IPv6 addresses are valid for the GRE-in-UDP tunnel and discard any packet for which this check fails. c. A GRE-in-UDP sender SHOULD use different IPv6 addresses for each GRE-in-UDP tunnel that uses UDP zero-checksum mode in order to strengthen the receiver's check of the IPv6 source address. When this is not possible, it is RECOMMENDED to use each source IPv6 address for as few UDP zero-checksum mode MPLS-in-UDP tunnels as is feasible. d. GRE-in-UDP sender and receiver MUST agree the key(s) used over the tunnel. The sender MUST insert a key on GRE header, and the receiver MUST check if the key in GRE header is valid for the tunnel and drop invalid packet. e. A GRE-in-UDP receiver node SHOULD only enable the use of UDP zero-checksum mode on a single UDP port and SHOULD NOT support any other use UDP zero-checksum mode on any other UDP port. f. A GRE-in-UDP sender SHOULD send GRE keepalive messages with a zero UDP checksum. GRE-in-UDP receiver that discovers an appreciable loss rate for keepalive packets MAY terminate the tunnel. g. GRE keepalive messages SHOULD include both UDP datagrams with a checksum and datagrams with a zero UDP checksum. This will enable the remote endpoint to distinguish between a path failure and the dropping of datagrams with a zero UDP checksum. h. Any middlebox support for MPLS-in-UDP with UDP zero-checksum mode for IPv6 MUST comply with requirements 1 and 8-10 in Section 5 of RFC 6936. (Editor note: the design team and authors need further discuss above requirements text) Crabbe, et al. [Page 6] Internet-Draft Generic UDP Encapsulation for IP Tunneling October 2014 The above requirements are intended to be in addition to the requirements specified in [RFC2460] as modified by [RFC6935] and the requirements specified in [RFC6936]. GRE-in-UDP over IPv6 does not include an additional integrity check because the above requirements in combination with the exceptions that restrict use of UDP zero-checksum mode to well-managed networks should not significantly increase the rate of corruption of UDP/GRE- encapsulated traffic by comparison to GRE-encapsulated traffic over similar well-managed networks and because GRE does not accumulate incorrect state as a consequence of GRE header corruption. Editor Note: The preceding paragraph addresses requirements 2-4 in Section 5 of [RFC 6936]. Requirement 5 in that section is addressed by the requirement e in this section. Requirements 6 and 7 in that section are covered by the requirements f and g in this section. Requirement 8-10 in that section is addressed by the requirement h in this section. In summary, UDP zero-checksum mode for IPv6 is allowed to be used with GRE-in-UDP when one of the two exceptions specified above applies, provided that additional requirements stated above are complied with. Otherwise the UDP checksum MUST be used for IPv6 as specified in [RFC0768] and [RFC2460]. This entire section and its requirements apply only to use of UDP zero-checksum mode for IPv6; they can be avoided by using the UDP checksum as specified in [RFC0768] and [RFC2460]. 3.2. Middlebox Considerations for IPv6 UDP Zero Checksums IPv6 datagrams with a zero UDP checksum will not be passed by any middlebox that validates the checksum based on [RFC2460] or that updates the UDP checksum field, such as NATs or firewalls. Changing this behavior would require such middleboxes to be updated to correctly handle datagrams with zero UDP checksums. The GRE-in-UDP encapsulation does not provide a mechanism to safely fall back to using a checksum when a path change occurs redirecting a tunnel over a path that includes a middlebox that discards IPv6 datagrams with a zero UDP checksum. In this case the GRE-in-UDP tunnel will be black-holed by that middlebox. Recommended changes to allow firewalls, NATs and other middleboxes to support use of an IPv6 zero UDP checksum are described in Section 5 of [RFC6936]. Crabbe, et al. [Page 7] Internet-Draft Generic UDP Encapsulation for IP Tunneling October 2014 3.3. GRE-in-UDP Encapsulation Format The format of the GRE-in-UDP encapsulation for both IPv4 and IPv6 outer headers is shown in the following figures: 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 IPv4 Header: +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Version| IHL |Type of Service| Total Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Identification |Flags| Fragment Offset | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Time to Live |Protcol=17(UDP)| Header Checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Source IPv4 Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Destination IPv4 Address | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ UDP Header: +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Source Port = XXXX | Dest Port = TBD | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | UDP Length | UDP Checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ GRE Header: +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |C| |K|S| Reserved0 | Ver | Protocol Type | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Checksum (optional) | Reserved1 (Optional) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Key (optional) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sequence Number (Optional) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1 UDP+GRE IPv4 headers Crabbe, et al. [Page 8] Internet-Draft Generic UDP Encapsulation for IP Tunneling October 2014 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 IPv6 Header: +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Version| Traffic Class | Flow Label | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Payload Length | NxtHdr=17(UDP)| Hop Limit | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + + | | + Outer Source IPv6 Address + | | + + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + + | | + Outer Destination IPv6 Address + | | + + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ UDP Header: +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Source Port = XXXX | Dest Port = TBD | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | UDP Length | UDP Checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ GRE Header: +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |C| |K|S| Reserved0 | Ver | Protocol Type | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Checksum (optional) | Reserved1 (Optional) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Key (optional) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sequence Number (Optional) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2 UDP+GRE IPv6 headers Crabbe, et al. [Page 9] Internet-Draft Generic UDP Encapsulation for IP Tunneling October 2014 The total overhead increase for a UDP+GRE tunnel without use of optional GRE fields, representing the lowest total overhead increase, is 32 bytes in the case of IPv4 and 52 bytes in the case of IPv6. The total overhead increase for a UDP+GRE tunnel with use of GRE Key, Sequence and Checksum Fields, representing the highest total overhead increase, is 44 bytes in the case of IPv4 and 64 bytes in the case of IPv6. 4. Encapsulation Considerations GRE-in-UDP encapsulation is used for single tunnel mechanism where both GRE and UDP header are required. The mechanism allows the tunneled traffic to be unicast, broadcast, or multicast traffic. Entropy may be generated from the header of tunneled unicast or broadcast/multicast packets at tunnel ingress. The mapping mechanism between the tunneled multicast traffic and the multicast capability in the IP network is transparent and independent to the encapsulation and is outside the scope of this document. The tunnel ingress SHOULD perform the fragmentation [GREMTU] on a packet before the encapsulation and factor in both GRE and UDP header bytes in the effective Maximum Transmission Unit (MTU) size. Not performing the fragmentation will cause the packets exceeding network MTU size to be dropped in the network. The tunnel ingress MUST use the same source UDP port for all packet fragments to ensure that the transit routers will forward the packet fragments on the same path. An operator should factor in the addition overhead bytes when considering an MTU size for the payload to reduce the likelihood of fragmentation. To ensure the tunneled traffic gets the same treatment over the IP network, prior to the encapsulation process, tunnel ingress should process the payload to get the proper parameters to fill into the IP header such as DiffServ [RFC2983]. Tunnel end points that support ECN MUST use the method described in [RFC6040] for ECN marking propagation. This process is outside of the scope of this document. Note that the IPv6 header [RFC2460] contains a flow label field that may be used for load balancing in an IPv6 network [RFC6438]. Thus in an IPv6 network, either GRE-in-UDP or flow labels may be used for Crabbe, et al. [Page 10] Internet-Draft Generic UDP Encapsulation for IP Tunneling October 2014 improving load balancing performance. Use of GRE-in-UDP encapsulation provides a unified hardware implementation for load balancing in an IP network independent of the IP version(s) in use. However IPv6 network require performing the UDP checksum, which may impact network performance and user experience. Thus, a flow label based load balancing may be a better approach in an IPv6 network. 5. Congestion Considerations Section 3.1.3 of RFC 5405 [RFC5405] discussed the congestion implications of UDP tunnels. As discussed in RFC 5405, because other flows can share the path with one or more UDP tunnels, congestion control [RFC2914] needs to be considered. A major motivation for encapsulating GRE in UDP is to provide a generic UDP tunnel protocol to tunnel a network protocol over IP network and improve the use of multipath (such as Equal Cost MultiPath, ECMP) in cases where traffic is to traverse routers which are able to hash on UDP Port and IP address. As such, in many cases this may reduce the occurrence of congestion and improve usage of available network capacity. However, it is also necessary to ensure that the network, including applications that use the network, responds appropriately in more difficult cases, such as when link or equipment failures have reduced the available capacity. The impact of congestion must be considered both in terms of the effect on the rest of the network of a UDP tunnel that is consuming excessive capacity, and in terms of the effect on the flows using the UDP tunnels. The potential impact of congestion from a UDP tunnel depends upon what sort of traffic is carried over the tunnel, as well as the path of the tunnel. GRE in UDP as a generic UDP tunnel mechanism can be used to carry a network protocol and traffic. If tunneled traffic is already congestion controlled, GRE in UDP tunnel generally does not need additional congestion control mechanisms. As specified in RFC 5405: IP-based traffic is generally assumed to be congestion-controlled, i.e., it is assumed that the transport protocols generating IP-based traffic at the sender already employ mechanisms that are sufficient to address congestion on the path. Consequently, a tunnel carrying. IP-based traffic should already interact appropriately with other traffic sharing the path, and specific congestion control mechanisms for the tunnel are not necessary. Crabbe, et al. [Page 11] Internet-Draft Generic UDP Encapsulation for IP Tunneling October 2014 For this reason, where GRE in UDP tunneling is used to carry IP traffic that is known to be congestion controlled, the tunnel MAY be used across any combination of a single service provider, multiple cooperating service providers, or across the general Internet. Internet IP traffic is generally assumed to be congestion-controlled. However, GRE in UDP tunneling is also used in many cases to carry traffic that is not necessarily congestion controlled. In such cases service providers and data center operators may avoid congestion by careful provisioning of their networks, by rate limiting of user data traffic, and/or by using Traffic Engineering tools to monitor the network segments and dynamically steers traffic away from the potential congested link in time. For this reason, where the GRE payload traffic is not congestion controlled, GRE in UDP tunnels MUST only be used within a single service provider that utilizes careful provisioning (e.g., rate limiting at the entries of the network while over-provisioning network capacity) to ensure against congestion, or within a limited number of service providers who closely cooperate in order to jointly provide this same careful provisioning. As such, GRE in UDP MUST NOT be used over the general Internet, or over non-cooperating ISPs, to carry traffic that is not congestion- controlled. Measures SHOULD be taken to prevent non-congestion-controlled GRE- over-UDP traffic from "escaping" to the general Internet, e.g.: o physical or logical isolation of the links carrying GRE-over-UDP from the general Internet, o deployment of packet filters that block the UDP ports assigned for GRE-over-UDP, o imposition of restrictions on GRE-over-UDP traffic by software tools used to set up GRE-over-UDP tunnels between specific end systems (as might be used within a single data center), and o use of a "Managed Circuit Breaker" for the tunneled traffic as described in [I-D.-tsvwg-circuit-breaker]. [Editor: the text in this section was derived from the text for mpls-in-udp. More work necessary to make general for this] Crabbe, et al. [Page 12] Internet-Draft Generic UDP Encapsulation for IP Tunneling October 2014 6. Backward Compatibility It is assumed that tunnel ingress routers must be upgraded in order to support the encapsulations described in this document. No change is required at transit routers to support forwarding of the encapsulation described in this document. If a router that is intended for use as a tunnel egress does not support the GRE-in-UDP encapsulation described in this document, it will not be listening on destination port [TBD]. In these cases, the router will conform to normal UDP processing and respond to the tunnel ingress with an ICMP message indicating "port unreachable" according to [RFC792]. Upon receiving this ICMP message, the tunnel ingress MUST NOT continue to use GRE-in-UDP encapsulation toward this tunnel egress without management intervention. 7. IANA Considerations IANA is requested to make the following allocation: Service Name: GRE-in-UDP Transport Protocol(s): UDP Assignee: IESG Contact: IETF Chair Description: GRE-in-UDP Encapsulation Reference: [This.I-D] Port Number: TBD Service Code: N/A Known Unauthorized Uses: N/A Assignment Notes: N/A 8. Security Considerations 8.1. Vulnerability Neither UDP nor GRE encapsulation effects security for the payload protocol. When using GRE-in-UDP, Network Security in a network is the same as that of a network using GRE. Use of ICMP for signaling of the GRE-in-UDP encapsulation capability adds a security concern. Upon receiving an ICMP message and before taking an action on it, the ingress MUST validate the IP address Crabbe, et al. [Page 13] Internet-Draft Generic UDP Encapsulation for IP Tunneling October 2014 originating against tunnel egress address and MUST evaluate the packet header returned in the ICMP payload to ensure the source port is the one used for this tunnel. The mechanism for performing this validation is out of the scope of this document. In an instance where the UDP src port is not set based on the flow invariant fields from the payload header, a random port SHOULD be selected in order to minimize the vulnerability to off-path attacks. [RFC6056] How the src port randomization occurs is outside scope of this document. Using one standardized value in UDP destination port for an encapsulation indication may increase the vulnerability of off-path attack. To overcome this, tunnel egress may request tunnel ingress using a different and specific value [RFC6056] in UDP destination port for the GRE-in-UDP encapsulation indication. How the tunnel end points communicate the value is outside scope of this document. This document does not require that the tunnel egress validates the IP source address of the tunneled packets (with the exception that the IPv6 source address MUST be validated when UDP zero-checksum mode is used with IPv6), but it should be understood that failure to do so presupposes that there is effective destination-based (or a combination of source-based and destination-based) filtering at the boundaries. 9. Acknowledgements Authors like to thank Vivek Kumar, Ron Bonica, Joe Touch, Ruediger Geib, Gorry Fairhurst, David Black, Lar Edds, Lloyd, and many others for their review and valuable input on this draft. Thank the design team led by David Black (members: Ross Callon, Gorry Fairhurst, Xiaohu Xu, Lucy Yong) to efficiently work out the descriptions for the congestion considerations and IPv6 UDP zero checksum. 10. Contributors The following people all contributed significantly to this document and are listed below in alphabetical order: Crabbe, et al. [Page 14] Internet-Draft Generic UDP Encapsulation for IP Tunneling October 2014 Ross Callon Juniper Networks 10 Technology Park Drive Westford, MA 01886 USA Email: rcallon@juniper.net David Black EMC Corporation 176 South Street Hopkinton, MA 01748 USA Email: david.black@emc.com John E. Drake Juniper Networks Email: jdrake@juniper.net Adrian Farrel Juniper Networks Email: adrian@olddog.co.uk Vishwas Manral Hewlett-Packard Corp. 3000 Hanover St, Palo Alto. Email: vishwas.manral@hp.com Carlos Pignataro Cisco Systems 7200-12 Kit Creek Road Research Triangle Park, NC 27709 USA EMail: cpignata@cisco.com Yongbing Fan China Telecom Guangzhou, China. Crabbe, et al. [Page 15] Internet-Draft Generic UDP Encapsulation for IP Tunneling October 2014 Phone: +86 20 38639121 Email: fanyb@gsta.com 11. References 11.1. Normative References [RFC768] Postel, J., "User Datagram Protocol", STD 6, RFC 768, August 1980. [RFC791] DARPA, "Internet Protocol", RFC791, September 1981 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC2119, March 1997. [RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P. Traina, "Generic Routing Encapsulation (GRE)", RFC 2784, March 2000. [RFC2890] Dommety, G., "Key and Sequence Number Extensions to GRE", RFC2890, September 2000. [RFC2983] Black, D., "Differentiated Services and Tunnels", RFC2983, October 2000. [RFC5405] Eggert, L., "Unicast UDP Usage Guideline for Application Designers", RFC5405, November 2008. [RFC6040] Briscoe, B., "Tunneling of Explicit Congestion Notification", RFC6040, November 2010 [RFC6438] Carpenter, B., Amante, S., "Using the IPv6 Flow Label for Equal Cost Multipath Routing and Link Aggregation in tunnels", RFC6438, November, 2011 11.2. Informative References [RFC792] Postel, J., "Internet Control Message Protocol", STD 5, RFC 792, September 1981. [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", RFC 2460, December 1998. [RFC3931] Lau, J., Townsley, M., and I. Goyret, "Layer Two Tunneling Protocol - Version 3 (L2TPv3)", RFC 3931, March 2005. Crabbe, et al. [Page 16] Internet-Draft Generic UDP Encapsulation for IP Tunneling October 2014 [RFC4023] Worster, T., Rekhter, Y., and E. Rosen, "Encapsulating MPLS in IP or Generic Routing Encapsulation (GRE)", RFC 4023, March 2005. [RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private Networks (VPNs)", RFC 4364, February 2006. [RFC4884] Bonica, R., Gan, D., Tappan, D., and C. Pignataro, "Extended ICMP to Support Multi-Part Messages", RFC 4884, April 2007. [RFC6056] Larsen, M. and Gont, F., "Recommendations for Transport- Protocol Port Randomization", RFC6056, January 2011 [RFC6790] Kompella, K., Drake, J., Amante, S., Henderickx, W., and L. Yong, "The Use of Entropy Labels in MPLS Forwarding", RFC 6790, November 2012. [GREMTU] Bonica, R., "A Fragmentation Strategy for Generic Routing Encapsulation (GRE)", draft-bonica-intara-gre-mtu, work in progress [CB] Fairhurst, G., "Network Transport Circuit Breakers", draft-fairhurst-tsvwg-circuit-breaker-01, work in progress 12. Authors' Addresses Edward Crabbe (editor) Email: edward.crabbe@gmail.com Lucy Yong (editor) Huawei Technologies, USA Email: lucy.yong@huawei.com Xiaohu Xu (editor) Huawei Technologies, Beijing, China Email: xuxiaohu@huawei.com Crabbe, et al. [Page 17] Internet-Draft Generic UDP Encapsulation for IP Tunneling October 2014 Gorry's comments - give an example of random constant value selection for UDP source port in the case where tunnel ingress can't get flow entropy - use "MUST" instead of "SHOULD" for requesting use of UDP checksum in IPv6 network - more concise text for congestion description; use some text in [RFC5405] - State what consequence without doing fragmentation - tunnel ingress actions upon receiving an ICMP msg - tunnel-in-tunnel case - CB does not describe the protocol to support CB, only the mechanism. UDP report protocol may be good fit. Crabbe, et al. [Page 18]