Internet Engineering Task Force R. Housley Internet-Draft SPYRUS December 26, 2000 S. Hollenbeck Expires: May 26, 2001 VeriSign, Inc. EtherIP: Tunneling Ethernet Frames in IP Datagrams Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. Abstract This document describes a protocol for tunneling Ethernet and IEEE 802.3 media access control frames in IP datagrams so that non-IP traffic can traverse an IP internet. Conventions Used In This Document 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]. Housley, Hollenbeck Expires May 26, 2001 [Page 1] Internet-Draft EtherIP December 26, 2000 1. Introduction The EtherIP protocol is used to tunnel Ethernet [DIX] and IEEE 802.3 [CSMA/CD] media access control (MAC) frames (including IEEE 802.1Q [VLAN] datagrams) across an IP internet. Tunneling is usually performed when the layer three protocol carried in the MAC frames is not IP or when encryption obscures the layer three protocol control information needed for routing. EtherIP may be implemented in an end station to enable tunneling for that single station, or it may be implemented in a bridge-like station to enable tunneling for multiple stations connected to a particular local area network (LAN) segment. EtherIP may be used to enable communications between stations that implement Ethernet or IEEE 802.3 with a layer three protocol other than IP. For example, two stations connected to different Ethernet LANs using the Xerox Network Systems Internetwork Datagram Protocol (IDP) [XNS] could employ EtherIP to enable communications across the Internet. EtherIP may be used to enable communications between stations that encrypt the Ethernet or IEEE 802.3 payload. Regardless of the layer three protocol used, encryption obscures the layer three protocol control information, making routing impossible. For example, two stations connected to different Ethernet LANs using IEEE 802.10b [SDE] could employ EtherIP to enable encrypted communications across the Internet. EtherIP may implemented in a single station to provide tunneling of Ethernet or IEEE 802.3 frames for either of the reasons stated above. Such implementations require processing rules to determine which MAC frames to tunnel and which MAC frames to bypass the tunnel processing. Most often, these processing rules are based on the destination address or the EtherType. EtherIP may be implemented in a bridge-like station to provide tunneling services for all stations connected to a particular LAN segment. Such implementations promiscuously listen to all of the traffic on the LAN segment, then apply processing rules to determine which MAC frames to tunnel and which MAC frames to ignore. MAC frames that require tunneling are encapsulated with EtherIP and IP, then transmitted to the local IP router for delivery to the bridge-like station serving the remote LAN. Most often, these processing rules are based on the source address, the destination address, or the EtherType. Care in establishing these rules must be exercised to ensure that the same MAC frame does not get transmitted endlessly between several bridge-like stations, especially when broadcast or multicast destination MAC addresses are used as selection criteria. Housley, Hollenbeck Expires May 26, 2001 [Page 2] Internet-Draft EtherIP December 26, 2000 2. Protocol Format EtherIP segments are sent and received as internet datagrams. An Internet Protocol (IP) header carries several information fields, including an identifier for the next level protocol. An EtherIP header follows the internet header, providing information specific to the EtherIP protocol. Internet Protocol version 4 (IPv4) [RFC791] defines an 8-bit field called "Protocol" to identify the next level protocol. Internet Protocol version 6 (IPv6) [RFC1883] defines the "Next Header" field for this same purpose. The value of this field MUST be set to 97 decimal (141 octal, 61 hex) to identify an EtherIP datagram. EtherIP datagrams contain an 8-bit header and a variable-length encapsulated Ethernet or IEEE 802.3 frame that immediately follows IP fields. +-----------------------+-----------------------------+ | | | | | IP | EtherIP Header | Encapsulated Ethernet Frame | | | | | +-----------------------+-----------------------------+ Figure 1: EtherIP Datagram Description The 8-bit EtherIP header field consists of two parts: a 4-bit version field that identifies the EtherIP protocol version and a 4-bit field reserved for future use. The value of the version field MUST be 2 (two, '0010' binary). The value of the reserved field MUST be 0 (zero). 0 1 2 3 4 5 6 7 +-----+-----+-----+-----+-----+-----+-----+-----+ | | | | VERSION | RESERVED | | | | +-----+-----+-----+-----+-----+-----+-----+-----+ Figure 2: EtherIP Header Format (in bits) Bits 0-3: Protocol version Bits 4-7: Reserved for future use The encapsulated Ethernet frame field contains a complete Ethernet or IEEE 802.3 frame of any type less the frame check sequence (FCS) value. The IP checksum does not provide integrity protection for the Ethernet/IEEE 802.3 frame, so some higher-layer protocol encapsulated by the Ethernet/IEEE 802.3 frame is expected to provide the integrity protection. Housley, Hollenbeck Expires May 26, 2001 [Page 3] Internet-Draft EtherIP December 26, 2000 3. Sending Procedures This section describes the processing to encapsulate an Ethernet or IEEE 802.3 MAC frame in an EtherIP datagram. First, the implementation determines whether the MAC frame requires tunneling. Then, if tunneling is required, the MAC frame is processed according to the steps provided in this section. Stations processing VLAN datagrams MAY need to examine the VLAN header to make appropriate tunneling decisions. An end station that implements EtherIP may tunnel some traffic, but not all traffic. Thus, the first step in processing a MAC frame is to determine if the frame needs to be tunneled or not. If the recipient station is connected to the same LAN as the source station, then tunneling is not needed. If the network connecting the stations can route the layer three protocol, then tunneling is not needed. Other environment specific criteria MAY also be applied. If tunneling is not needed, skip all EtherIP processing and perform normal data link layer processing to transmit the MAC frame. Otherwise, follow the steps described below. A bridge-like station promiscuously listens to all of the MAC frames on the LAN. Each MAC frame read from the LAN is examined to determine if it needs to be tunneled. If the recipient station is connected to the same LAN as the source station, then tunneling is not needed. If the destination MAC address is a router serving the LAN, then tunneling is not needed. Other environment specific criteria MAY also be applied. If tunneling is not needed, then discard the MAC frame. Otherwise, follow the steps described below. 1. Prepend the EtherIP single-byte header to the MAC frame. The EtherIP Version field MUST be set to 2 (two), and the EtherIP Reserved field MUST be set to 0 (zero). The MAC frame MUST not include the FCS. 2. Determine the destination IP address of the remote EtherIP station. This address is usually determined from the destination MAC address. 3. Prepend the IP address to the EtherIP datagram. The destination address is determined in the previous step, and the IPv4 Protocol or the IPv6 Next Header field MUST be set to 97 decimal. 4. Perform normal data link layer processing to transmit the resulting IP datagram to the IP router serving the LAN. Housley, Hollenbeck Expires May 26, 2001 [Page 4] Internet-Draft EtherIP December 26, 2000 4. Receiving Procedures This section describes the processing to decapsulate an Ethernet or IEEE 802.3 MAC frame from an EtherIP datagram. Upon reception of an IPv4 datagram with the Protocol field or an IPv6 datagram with the Next Header field set to 97 decimal, the MAC frame is processed according to the steps provided in this section. The first step in processing a received MAC frame is to determine if the frame needs to be decapsulated or not. If the recipient station is connected to the same LAN as the source station, then decapsulation is not needed. If the network connecting the stations can route the layer three protocol, then decapsulation is not needed. Other environment specific criteria MAY also be applied. If decapsulation is not needed, skip all EtherIP processing and perform normal data link layer processing to receive the MAC frame. Otherwise, follow the steps described below. Since a bridge-like station promiscuously listens to all of the MAC frames on the LAN, it may need to separate the MAC frames that encapsulate IP datagrams addressed to it from MAC frames that are candidates for decapsulation. The process for identifying MAC frames that are candidates for decapsulation is described below. 1. Perform normal data link layer processing to receive a suspected EtherIP datagram from the IP router serving the LAN. Ignore frames that do not contain an IP datagram. 2. Examine the IPv4 protocol field or the IPv6 Next Header field to confirm that the value of the field is 97 decimal. Ignore the frame if not. 3. Examine the EtherIP single-byte header. Confirm that the value of the version field is 2 (two), and that the value of the Reserved field is 0 (zero). The frame MUST be discarded if these values are not found. 4. Extract the encapsulated MAC frame from the EtherIP datagram. Note that the extracted frame MUST NOT include a FCS value. 5. Perform normal data link layer processing to transmit the extracted MAC frame to the destination station on the LAN. The FCS MUST be calculated and appended to the frame as part of the data link layer transmission processing. Housley, Hollenbeck Expires May 26, 2001 [Page 5] Internet-Draft EtherIP December 26, 2000 5. IANA Considerations IANA has assigned IP protocol value 97 decimal for EtherIP. No further action or review is required. 6. Security Considerations EtherIP can be used to enable the transfer of encrypted Ethernet or IEEE 802.3 frame payloads. In this regard, EtherIP can improve security. However, if a firewall permits EtherIP traffic to pass in and out of a protected enclave, arbitrary communications are enabled. Therefore, if a firewall is configured to permit communication using EtherIP, then additional checking of each frame is probably necessary to ensure that the security policy that the firewall is installed to enforce is not violated. 7. Acknowledgements This document describes a protocol that was originally designed and implemented by Xerox Special Information Systems in 1991 and 1992. An earlier version of the protocol was provided as part of the Xerox Ethernet Tunnel (XET). Housley, Hollenbeck Expires May 26, 2001 [Page 6] Internet-Draft EtherIP December 26, 2000 8. References [CSMA/CD] Institute of Electrical and Electronics Engineers: "Carrier Sense Multiple Access with Collision Detection (CSMA/CD) Access Method and Physical Layer Specifications", ANSI/IEEE Std 802.3-1985, 1985. [DIX] Digital Equipment Corporation, Intel Corporation, and Xerox Corporation: "The Ethernet -- A Local Area Network: Data Link Layer and Physical Layer (Version 2.0)", November 1982. [RFC791] J. Postel: "Internet Protocol", RFC 791, September 1981. [RFC1883] S. Deering and R. Hinden: "Internet Protocol, Version 6 (IPv6) Specification", RFC 1883, December 1995. [RFC2119] S. Bradner: "Key Words for Use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [SDE] Institute of Electrical and Electronics Engineers: "Interoperable LAN/MAN Security (SILS) Secure Data Exchange (SDE) (Clause 2)", IEEE Std 802.10b-1992, 1992. [XNS] Xerox Corporation: "Internet Transport Protocols", XSIS 028112, December 1981. [VLAN] Institute of Electrical and Electronics Engineers: "IEEE Standard for Local and Metropolitan Area Networks: Virtual Bridge Local Area Networks", ANSI/IEEE Std 802.1Q-1998, 1998. Housley, Hollenbeck Expires May 26, 2001 [Page 7] Internet-Draft EtherIP December 26, 2000 9. Author's Address Russell Housley SPYRUS 381 Elden Street Suite 1120 Herndon, VA 20170 USA housley@spyrus.com Scott Hollenbeck VeriSign Global Registry Services 21345 Ridgetop Circle Dulles, VA 20166-6503 USA shollenbeck@verisign.com Housley, Hollenbeck Expires May 26, 2001 [Page 8] Internet-Draft EtherIP December 26, 2000 10. Full Copyright Statement Copyright (C) The Internet Society 2000. All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Acknowledgement Funding for the RFC Editor function is currently provided by the Internet Society. Housley, Hollenbeck Expires May 26, 2001 [Page 9]