Ok - four different encapsulation types are commonly found on an "ethernet" network. All versions have a frame format that includes
* preamble * destination MAC address * source MAC address * a field who's purpose differs with encapsulation type * payload * frame check sequence (CRC) The encapsulation types differ as follows * Ethernet II (Cisco keyword "arpa") - uses a payload length field. Since the ether MTU is 1518 with 18 octets of overhead, this field is never more than 1500. * 802.3 Raw - This type is said to be raw because service access points are not specified, as in 802.2 or SNAP. The field used for length in ethernet II carries instead "type" information that specifies the layer three protocol. Key values are (in hex) * 802.2 (SAP) - If the 802.3 type field specifies SAP, fields specifying source and destination service access points (DSAP and SSAP) have been inserted between the length field and the payload. The service access points specify the higher level entity that will process the message - thus, they effectively specify the higher level protocol encapsulated in the frame. * SNAP - If the LLC header (DSAP and SSAP are both AA), a SNAP sub header between the SAP header and payload add a 5 byte field that allows specification of additional layer three protocol types. CCIE TB wrote: > Microsoft devices defaults to 802.2 frame format when using NWLink, I'm > having a problem categorizing this type. > > Ethernet II ------> uses Type instead of Length > 802.3 ------------> uses Length and SSAP/DSAP > SNAP ------------> uses Length with fixed SSAP/DSAP and adds SNAP header. > Based on this what is the format of 802.2 frames -- Jason Boson BCMSN1 BSCN2 BSCI2 practice tests E-Quizware CCIE practice test Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=25932&t=25925 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
