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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-01.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, such as ESIS 112 and ISIS which are carried as CLNS packets, have no reserved 113 Ethertype. Such packets can only use the IEEE 802.3/802.2 encoding, 114 and so are limited in length to 1500 bytes. 116 Ethernet_II frames have no length field. Protocols encapsulated in 117 Ethernet II frames, such as IP, are not limited in length to 1500 118 bytes by framing. 120 6. Proposed Ethernet Frame Extension 122 Large 802.3 and Ethernet_II frames can be supported by the following: 124 + Define an Ethertype for 802.3, 0x8870, and encode large frames 125 (where the data field is greater than 1500 bytes), 126 exclusive of the Destination MAC address, Source MAC address, 127 and Data length fields, within Ethernet II. 129 Large 802.3/802.2 frames would have the following fields: 131 +----+----+------+------+------+------+------+-----+ 132 | DA | SA | Type | DSAP | SSAP | Ctrl | Data | FCS | 133 +----+----+------+------+------+------+------+-----+ 134 === 802.2 Header === 136 DA Destination MAC Address (6 bytes) 137 SA Source MAC Address (6 bytes) 138 Type 0x8870 (Ethertype) (2 bytes) 139 DSAP 802.2 Destination Service Access Point (1 byte) 140 SSAP 802.2 Source Service Access Point (1 byte) 141 Ctrl 802.2 Control Field (1 byte) 142 Data Protocol Data ( > 46 bytes) 143 FCS Frame Checksum (4 bytes) 145 + Allow Ethernet II frames to have payloads greater than 1500 bytes. 147 There is no loss of information from 802.3/802.2 frames. Although 148 the 802.3 length field is missing, the frame length is known by 149 virtue of the frame being accepted by the network interface. 151 In this manner, all Ethernet II frames, including large 802.3 152 packets, can be longer than 1500 bytes, yet are uniquely identified. 154 7. References 156 [ETH] "The Ethernet - A Local Area Network", version 1.0, Digital 157 Equipment Corporation, September 1980, and "The Ethernet, A Local 158 Area Network" Data Link Layer and Physical Layer Specifications", 159 Digital, Intel, and Xerox, November, 1982. 161 [RFC894] IETF RFC 894 163 [IEEE802.3] IEEE Std 802.3 165 [IEEE802] IEEE Std 802 167 [IEEE802.3Z] IEEE Std 802.3z 169 [EXT.FRAME] "Use of Extended Frame Sizes in Ethernet Networks", draft 170 2.1, Alteon Networks, Inc. 172 8. Author's Addresses 174 Mike O'Dell 175 UUNET an MCI WorldCom Company 176 3060 WIllaims Drive 177 Fairfax, Va. 22031-4648 178 703-206-5890 179 email: mo@uu.net 181 Jed Kaplan 182 UUNET an MCI WorldCom Company 183 3060 WIllaims Drive 184 Fairfax, Va. 22031-4648 185 914-701-5309 186 email: jkaplan@uu.net 188 John Hayes 189 Alteon WebSystems, Inc. 190 50 Great Oaks Blvd. 191 San Jose, CA 95119 192 408-360-5507 193 email: hayes@alteon.com 195 Ted Schroeder 196 Alteon WebSystems, Inc. 197 50 Great Oaks Blvd. 198 San Jose, CA 95119 199 408-360-5500 200 email: ted@alteon.com 202 P.J. Singh 203 Packet Engines, Inc. 204 11707 East Sprague #101 205 Spokane WA 99206 206 509-777-7000 207 email: pjsingh@packetengines.com 209 Daemon Morrell 210 Juniper Networks, Inc. 211 12343-D Sunrise Valley Drive 212 Reston, VA 20191 213 email: dmorrell@juniper.net 215 Jennifer Hsu 216 jhsu@mur.com