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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 Network Working Group Mike O'Dell 2 Internet Draft Jed Kaplan 3 Expiration Date: November 1999 UUNET Technologies, Inc. 5 John Hayes 6 Ted Schroeder 7 Alteon WebSystems, Inc. 9 P.J. Singh 10 Packet Engines, Inc. 12 Daemon Morrell 13 Juniper Networks, Inc. 15 Jennifer Hsu 17 Extended Ethernet Frame Size Support 19 draft-kaplan-isis-ext-eth-02.txt 21 1. Status of this Memo 23 This document is an Internet-Draft and is in full conformance with 24 all provisions of Section 10 of RFC2026. 26 Internet-Drafts are working documents of the Internet Engineering 27 Task Force (IETF), its areas, and its working groups. Note that 28 other groups may also distribute working documents as Internet- 29 Drafts. 31 Internet-Drafts are draft documents valid for a maximum of six months 32 and may be updated, replaced, or obsoleted by other documents at any 33 time. It is inappropriate to use Internet-Drafts as reference 34 material or to cite them other than as "work in progress." 36 The list of current Internet-Drafts can be accessed at 37 http://www.ietf.org/ietf/lid-abstracts.txt 39 The list of Internet-Draft Shadow Directories can be accessed at 40 http://www.ietf.org/shadow.html 42 2. Abstract 44 This document presents an extension to current Ethernet Frame 45 standards to support payloads greater than 1500 Bytes for Ethernet_II 46 and 802.3 frames. This is useful for Gigabit Ethernet technology, 47 providing a means to carry large MTU packets without fragmentation 48 over a high-speed broadcast network. 50 3. Overview 52 There are two fundamental frame types defined for Ethernet: 53 Ethernet II [ETH] [RFC894] and 802.3 [IEEE802.3]. 802.3 headers 54 may be followed by a Logical Link Control header, 55 802.2 [IEEE802.2]. Both types of encapsulations can co-exist on 56 the same media at the same time. Encodings for Ethernet II and 802.3 57 frames evolved such that, as long as payloads were less than 1500 58 bytes, Ethernet II frames could always be distinguished from 59 IEEE 802.3 frames. 61 However, when the payload is greater than 1500 bytes frames may 62 not be uniquely distinguishable as conforming to Ethernet II or 63 802.3 formats. This document extends the Ethernet frame format 64 to allow Ethernet_II or 802.3 frame payloads larger than 1500 bytes 65 to be uniquely distinguished. 67 4. Ethernet Frame Formats 69 A. Ethernet II 71 +----+----+------+------+-----+ 72 | DA | SA | Type | Data | FCS | 73 +----+----+------+------+-----+ 75 DA Destination MAC Address (6 bytes) 76 SA Source MAC Address (6 bytes) 77 Type Protocol Type (2 bytes) 78 Data Protocol Data (46 - 1500 bytes) 79 FCS Frame Checksum (4 bytes) 81 B. IEEE 802.3 and derivatives 83 +----+----+------+------+-----+ 84 | DA | SA | Len | Data | FCS | 85 +----+----+------+------+-----+ 87 DA Destination MAC Address (6 bytes) 88 SA Source MAC Address (6 bytes) 89 Len Length of Data field (2 bytes) 90 Data Protocol Data (46 - 1500 bytes) 91 FCS Frame Checksum (4 bytes) 93 The derivatives include LLC (802.2) and SNAP which prefix the 94 data field with an LLC header. In these instances the Len field 95 then corresponds to the combined size of both the data portion 96 of the frame and the LLC header. 98 On reception, the two formats are differentiated based on the 99 magnitude of the Type/Length field, as follows: 101 > 1500 bytes: value corresponds to a type field. The frame is an 102 Ethernet II frame, with type values starting 103 at 1536 (600 hex). 105 <= 1500 bytes: value corresponds to a length field. The frame is 106 an IEEE 802.3 format (or derivative) with a maximum 107 data length of 1500 bytes. 109 5. Problem with Large 802.3 Frames in the presence of Ethernet_II Frames 111 Some protocols commonly used in the Internet have no reserved Ethertype. 112 An example is the set of ISO Network layer protocols, of which 113 ISIS is a member. Such protocols are only defined to use the IEEE 114 802.3/802.2 encoding, and so their packets are limited in length to 115 1500 bytes. 117 Ethernet_II frames have no length field. Protocols encapsulated in 118 Ethernet II frames, such as IP, are not limited in length to 1500 119 bytes by framing. 121 6. Proposed Ethernet Frame Extension 123 Large 802.3 and Ethernet_II frames can be supported by the following: 125 + Define an Ethertype for 802.3, 0x8870, and encode large frames 126 (where the data field is greater than 1500 bytes), 127 exclusive of the Destination MAC address, Source MAC address, 128 and Data length fields, within Ethernet II. 130 Large 802.3/802.2 frames would have the following fields: 132 +----+----+------+------+------+------+------+-----+ 133 | DA | SA | Type | DSAP | SSAP | Ctrl | Data | FCS | 134 +----+----+------+------+------+------+------+-----+ 135 === 802.2 Header === 137 DA Destination MAC Address (6 bytes) 138 SA Source MAC Address (6 bytes) 139 Type 0x8870 (Ethertype) (2 bytes) 140 DSAP 802.2 Destination Service Access Point (1 byte) 141 SSAP 802.2 Source Service Access Point (1 byte) 142 Ctrl 802.2 Control Field (1 byte) 143 Data Protocol Data ( > 46 bytes) 144 FCS Frame Checksum (4 bytes) 146 + Allow Ethernet II frames to have payloads greater than 1500 bytes. 148 There is no loss of information from 802.3/802.2 frames. Although 149 the 802.3 length field is missing, the frame length is known by 150 virtue of the frame being accepted by the network interface. 152 In this manner, all Ethernet II frames, including large 802.3 153 packets, can be longer than 1500 bytes, yet are uniquely identified. 155 7. References 157 [ETH] "The Ethernet - A Local Area Network", version 1.0, Digital 158 Equipment Corporation, September 1980, and "The Ethernet, A Local 159 Area Network" Data Link Layer and Physical Layer Specifications", 160 Digital, Intel, and Xerox, November, 1982. 162 [RFC894] IETF RFC 894 164 [IEEE802.3] IEEE Std 802.3 166 [IEEE802] IEEE Std 802 168 [IEEE802.3Z] IEEE Std 802.3z 170 [EXT.FRAME] "Use of Extended Frame Sizes in Ethernet Networks", draft 171 2.1, Alteon Networks, Inc. 173 8. Author's Addresses 175 Mike O'Dell 176 UUNET an MCI WorldCom Company 177 3060 WIllaims Drive 178 Fairfax, Va. 22031-4648 179 703-206-5890 180 email: mo@uu.net 182 Jed Kaplan 183 UUNET an MCI WorldCom Company 184 3060 WIllaims Drive 185 Fairfax, Va. 22031-4648 186 914-701-5309 187 email: jkaplan@uu.net 189 John Hayes 190 Alteon WebSystems, Inc. 191 50 Great Oaks Blvd. 192 San Jose, CA 95119 193 408-360-5507 194 email: hayes@alteon.com 196 Ted Schroeder 197 Alteon WebSystems, Inc. 198 50 Great Oaks Blvd. 199 San Jose, CA 95119 200 408-360-5500 201 email: ted@alteon.com 203 P.J. Singh 204 Packet Engines, Inc. 205 11707 East Sprague #101 206 Spokane WA 99206 207 509-777-7000 208 email: pjsingh@packetengines.com 210 Daemon Morrell 211 Juniper Networks, Inc. 212 12343-D Sunrise Valley Drive 213 Reston, VA 20191 214 email: dmorrell@juniper.net 216 Jennifer Hsu 217 jhsu@mur.com