IEEE 802.1D, which specifies source-route bridging, supports 13 bridges, as you say. IBM was involved in developing that specification. I was there and I got the impression that at least the engineers at the meetings intended for the older proprietary IBM specifications to go away. Whether that really happened or not I don't know.
IEEE 802.5 says that the RI is 0 to 30 octets in the 1992 version. See clause 3.1.1. In the 1998 version, I just discovered, they removed that statement and say see clause 4.2.1. for length information. Clause 4.2.1 talks about the token holding timer and says the maximum octet count is 4550 for 4 Mbps and 18,200 for 16 Mbps. (They don't address the length of just the RI part). Before IEEE published Annex C of 802.1D (the source-routing spec), there were many preliminary documents about source-routing that said IEEE 802.5 at the top. These were never standardized. If you are looking at one of those, it may match what some vendors implemented, but it is not standard. The members of the 802.5 committee that were doing this work formed the new committee that wrote the spec that got added to the 802.1D spec. They were now allowed by the head haunchos to include bridging info in 802.5. (Note that they were also not allowed to specify pure source-route bridging. It's really source-route transparent bridging that is specified by IEEE). What does Cisco support? That's what really matters in this context! I don't believe I have ever worked on a network that had more than 7 bridges but I think Cisco would support more since they are IEEE-compatible?? Correct me if I'm wrong on that. As far as certification tests, you would have to think about all the misconceptions and old documentation that the test writer was using. ;-) Priscilla At 02:19 AM 1/3/02, Fred Ingham wrote: >Yes the spec says the length values are even values between 2 and 30, >but I have never seen any support for greater than 7 hops (maybe a >sheltered existence). Isn't the practical limit still the original IBM >spec with the length limit of 18? The 802.5 spec says ".. 18 bytes >being the minimum that must be supported." Would you really want a >network with 13 hops? > >And if there is a test question on max hops would you answer 7 or 13? > >Cheers, Fred. > > > >Priscilla Oppenheimer wrote: > > > > The Length field in the RC field indicates the total length of the RIF. > > Length values will be even values between 2 and 30 inclusive. > > > > Source-route bridging is documented in Annex C of IEEE 802.1D MAC Bridges. > > You can get it for free now from IEEE. There's no need to rely on the > > sloppy work of authors who pump out multiple books per year. ;-) > > > > Get the IEEE docs here: > > > > http://standards.ieee.org/getieee802/ > > > > Priscilla > > > > At 08:04 PM 1/1/02, Jason wrote: > > >All, > > > > > >Is the length field in the RC of a RIF the total size of the RIF or the > > >total size of the RD? > > > > > >According to the Rossi paper it is the total length of the RIF. > > > > > > Pg 5 "Bits 12-8 (next 5) bits descrige the total length of the >RIF > > >represented in bytes" > > > > > > Example from the Rossi paper : 0830 00a1 014f 01e0 (Page 5) > > > > > >However, in the Lammle/Swartz Study guide it is the total length of the >RD. > > > > > > Pg 694 "The Length field is the number of bytes used by the route > > >descriptors." > > > > > > Example from the Study Guide : 0490 020b 1000 (answer C question > > 20) > > > > > >Any and all help would be appreciated. > > > > > >Thanks > > >js > > ________________________ > > > > Priscilla Oppenheimer > > http://www.priscilla.com ________________________ Priscilla Oppenheimer http://www.priscilla.com Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=30814&t=30637 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
