>At 02:50 AM 1/9/02, Madisa Ramagoffu wrote: >>I have this question for you pls help >> >>In a token ring environment a sender send a packet to a destination >>with the ff in a packet > >Where is FF in the packet? That's just one byte. Is it a one-byte field >somewhere? In decimal, it's 255. Where might that appear? Or do you mean >that the Destination Address is all FFs. The Destination Address is 48 >bits. Each numeral represents one nibble (4 bits). So a Destination Address >of broadcast is: > >FF FF FF FF FF FF > >You will see many books that get this wrong and don't put enough FFs.
So you'd give such books a grade of F? > > >>Everything specified excerpt the dsap >>DSAP ???? >>da specified >>sa specified >>SSAP specified >> > >The recipient wouldn't be able to figure out that the DSAP was missing. The >bytes are processed serially. The first byte that follows Source Address >(or Routing Info, if present) would be considered the DSAP even if the >source somehow forgot to actually insert a DSAP. > >DSAP values could be: > >00 This is a null SAP, but I think it does have meaning in SNA >FF Broadcast. This means go to all processes on the recipient device. >42 BPDU >06 IP >F0 NetBIOS >E0 IPX >AA SNAP > >SNA also uses 04, 05, 08, and 0C > > > >>The question . what will happen to the packet if the DASP is not >>specified???? > >It can't not be specified from the recipient's viewpoint. The frame could >be just a MAC frame used for Token Ring processing rather than to carry >upper-layer data. In that case, MAC data would follow the Source Address, >rather than a DSAP. > >The first two bits of the Frame Control byte specify whether the frame is a >MAC (overhead) frame or upper-layer data carried in LLC. > >00 MAC >01 LLC > >>Is the packet going to be copied ? > >If you are talking about the setting of the Frame Copied bits, this happens >at the MAC layer (not the LLC layer). If a device recognizes that the frame >is for it, it sets the Address Recognized bits. It also sets the Frame >Copied bits unless it doesn't have enough buffer space to actually copy the >frame. (You may want to look into the special case of a bridge and whether >it should set the Address Recognized and Frame Copied when forwarding a >frame). > >>Is the packet going to be dropped ? >>Will it wait for the next packet or request a retransmit?? > >It certainly won't request a retransmit. This is a LAN data-link-layer >we're talking about. > >>What about the A C bit ? > >There's no such thing. You're probably thinking of the Address Recognized >or the Frame Copied bits, or maybe the Access Control byte at the beginning >of the frame. > > >>Pls send me any information or links I can read if you have . > >See IEEE 802.5. It's available here: http://standards.ieee.org/getieee802/ > >Also, there's some white paper that everyone always recommends by Rossi. >It's on Token Ring. Search the archives or ask the group. > >You should probably wait until Cisco finally takes Token Ring off the CCIE >tests. What's the point in learning all this? It's not going to help you be >a better network engineer!? ;-) Instead focus on general principles. What >is a Destination Address? What is its format? What is a DSAP? What is its >format? What is its purpose? What is LLC? How does a recipient process a >received frame? ETC. > >Good luck! > >Priscilla >________________________ > >Priscilla Oppenheimer >http://www.priscilla.com Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=31441&t=31358 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
