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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 Jennifer Hsu 13 Juniper Networks, Inc. 15 Extended Ethernet Frame Size Support 17 draft-kaplan-isis-ext-eth-00.txt 19 1. Status of this Memo 21 This document is an Internet-Draft and is in full conformance with 22 all provisions of Section 10 of RFC2026. 24 Internet-Drafts are working documents of the Internet Engineering 25 Task Force (IETF), its areas, and its working groups. Note that 26 other groups may also distribute working documents as Internet- 27 Drafts. 29 Internet-Drafts are draft documents valid for a maximum of six months 30 and may be updated, replaced, or obsoleted by other documents at any 31 time. It is inappropriate to use Internet-Drafts as reference 32 material or to cite them other than as "work in progress." 34 The list of current Internet-Drafts can be accessed at 35 http://www.ietf.org/ietf/lid-abstracts.txt 37 The list of Internet-Draft Shadow Directories can be accessed at 38 http://www.ietf.org/shadow.html 40 2. Abstract 42 This document presents an extension to current Ethernet Frame 43 standards to support payloads greater than 1500 Bytes for Ethernet_II 44 and 802.3 frames. This is useful for Gigabit Ethernet technology, 45 providing a means to carry large MTU packets without fragmentation 46 over a high-speed broadcast network. 48 3. Overview 50 There are two fundamental frame types defined for Ethernet: 51 Ethernet II [ETH] [RFC894] and 802.3 [IEEE802.3]. 802.3 headers 52 may be followed by a Logical Link Control header, 53 802.2 [IEEE802.2]. Both types of encapsulations can co-exist on 54 the same media at the same time. Encodings for Ethernet II and 802.3 55 frames evolved such that, as long as payloads were less than 1500 56 bytes, Ethernet II frames could always be distinguished from 57 IEEE 802.3 frames. 59 However, when the payload is greater than 1500 bytes frames may 60 not be uniquely distinguishable as conforming to Ethernet II or 61 802.3 formats. This document extends the Ethernet frame format 62 to allow Ethernet_II or 802.3 frame payloads larger than 1500 bytes 63 to be uniquely distinguished. 65 4. Ethernet Frame Formats 67 A. Ethernet II 69 +----+----+------+------+-----+ 70 | DA | SA | Type | Data | FCS | 71 +----+----+------+------+-----+ 73 DA Destination MAC Address (6 bytes) 74 SA Source MAC Address (6 bytes) 75 Type Protocol Type (2 bytes) 76 Data Protocol Data (46 - 1500 bytes) 77 FCS Frame Checksum (4 bytes) 79 B. IEEE 802.3 and derivatives 81 +----+----+------+------+-----+ 82 | DA | SA | Len | Data | FCS | 83 +----+----+------+------+-----+ 85 DA Destination MAC Address (6 bytes) 86 SA Source MAC Address (6 bytes) 87 Len Length of Data field (2 bytes) 88 Data Protocol Data (46 - 1500 bytes) 89 FCS Frame Checksum (4 bytes) 91 The derivatives include LLC (802.2) and SNAP which prefix the 92 data field with an LLC header. In these instances the Len field 93 then corresponds to the combined size of both the data portion 94 of the frame and the LLC header. 96 On reception, the two formats are differentiated based on the 97 magnitude of the Type/Length field, as follows: 99 > 1500 bytes: value corresponds to a type field. The frame is an 100 Ethernet II frame, with type values starting 101 at 1536 (600 hex). 103 <= 1500 bytes: value corresponds to a length field. The frame is 104 an IEEE 802.3 format (or derivative) with a maximum 105 data length of 1500 bytes. 107 5. Problem with Large 802.3 Frames in the presence of Ethernet_II Frames 109 Some protocols commonly used in the Internet, such as ESIS 110 and ISIS which are carried as CLNS packets, have no reserved 111 Ethertype. Such packets can only use the IEEE 802.3/802.2 encoding, 112 and so are limited in length to 1500 bytes. 114 Ethernet_II frames have no length field. Protocols encapsulated in 115 Ethernet II frames, such as IP, are not limited in length to 1500 116 bytes by framing. 118 6. Proposed Ethernet Frame Extension 120 Large 802.3 and Ethernet_II frames can be supported by the following: 122 + Define an Ethertype for 802.3, 0x8870, and encode large frames 123 (where the data field is greater than 1500 bytes), 124 exclusive of the Destination MAC address, Source MAC address, 125 and Data length fields, within Ethernet II. 127 Large 802.3/802.2 frames would have the following fields: 129 +----+----+------+------+------+------+------+-----+ 130 | DA | SA | Type | DSAP | SSAP | Ctrl | Data | FCS | 131 +----+----+------+------+------+------+------+-----+ 132 === 802.2 Header === 134 DA Destination MAC Address (6 bytes) 135 SA Source MAC Address (6 bytes) 136 Type 0x8870 (Ethertype) (2 bytes) 137 DSAP 802.2 Destination Service Access Point (1 byte) 138 SSAP 802.2 Source Service Access Point (1 byte) 139 Ctrl 802.2 Control Field (1 byte) 140 Data Protocol Data ( > 46 bytes) 141 FCS Frame Checksum (4 bytes) 143 + Allow Ethernet II frames to have payloads greater than 1500 bytes. 145 There is no loss of information from 802.3/802.2 frames. Although 146 the 802.3 length field is missing, the frame length is known by 147 virtue of the frame being accepted by the network interface. 149 In this manner, all Ethernet II frames, including large 802.3 150 packets, can be longer than 1500 bytes, yet are uniquely identified. 152 7. References 154 [ETH] "The Ethernet - A Local Area Network", version 1.0, Digital 155 Equipment Corporation, September 1980, and "The Ethernet, A Local 156 Area Network" Data Link Layer and Physical Layer Specifications", 157 Digital, Intel, and Xerox, November, 1982. 159 [RFC894] IETF RFC 894 161 [IEEE802.3] IEEE Std 802.3 163 [IEEE802] IEEE Std 802 165 [IEEE802.3Z] IEEE Std 802.3z 167 [EXT.FRAME] "Use of Extended Frame Sizes in Ethernet Networks", draft 168 2.1, Alteon Networks, Inc. 170 8. Author's Addresses 172 Mike O'Dell 173 UUNET an MCI WorldCom Company 174 3060 WIllaims Drive 175 Fairfax, Va. 22031-4648 176 703-206-5890 177 email: mo@uu.net 179 Jed Kaplan 180 UUNET an MCI WorldCom Company 181 3060 WIllaims Drive 182 Fairfax, Va. 22031-4648 183 914-701-5309 184 email: jkaplan@uu.net 186 John Hayes 187 Alteon WebSystems, Inc. 188 50 Great Oaks Blvd. 189 San Jose, CA 95119 190 408-360-5507 191 email: hayes@alteon.com 193 Ted Schroeder 194 Alteon WebSystems, Inc. 195 50 Great Oaks Blvd. 196 San Jose, CA 95119 197 408-360-5500 198 email: ted@alteon.com 200 P.J. Singh 201 Packet Engines, Inc. 202 11707 East Sprague #101 203 Spokane WA 99206 204 509-777-7000 205 email: pjsingh@packetengines.com 207 Jennifer Hsu 208 Juniper Networks, Inc. 209 385 Ravendale Drive 210 Mountain View, CA 94043 211 301-924-7237 212 email: jhsu@juniper.net