At 07:25 AM 5/23/02, Ivan wrote: >Hi all, > >I have a interest question, doesn't any one know the answer? > >A router is being used as a translation bridge between a Token Ring network >and an Ethernet network. Host X on the Token ring sends a packet to Host Y >on the Ethernet. The soursce MAC address of the packet is 400.a089.0002.
That's not a valid address. A MAC address is 48 bits or 6 bytes. In hex a byte is written with 2 digits. So the address must have 12 digits. I assume you are missing a 0 and that you meant to say: 4000.a089.0002 The bridge will translate the non-canonical address to canonical (see my other message and numerous other messages on that computing 101 topic). On the other hand, maybe the question expects you to know these other details: The first byte of that address in binary is: 01000000 Token Ring transmits the most significant bit first. (the one in the 2^7 position). IEEE says that the first bit transmitted is the Specific/Group bit. (A group address is used for multicast and broadcast). 0 = Specific 1 = Group So this is a specific address. No problem. Ethernet can handle that (and could handle a multicast or broadcast too, of course.) IEEE says that the second bit transmitted is the Globally Administered/Locally Administered bit. 0 = Global 1 = Local So this is a locally-administered address. Although IEEE 802.3 (Ethernet) does officially support locally-administered addresses, they aren't often used on Ethernet. So that's a minor issue. The second byte is 00000000 IEEE 802.5 (Token Ring) says that the least significant bit of the second byte is the Functional/Non Functional address. IEEE 802.3 (Ethernet) does not say this and does not support functional addresses. 0 = Functional 1 = Non functional So here we have a slightly more interesting issue. This is a functional address. Ethernet won't recognize that it's a functional address, however. From a troubleshooting viewpoint, you would want to figure out what "function" this was supposed to carry out on the Token Ring side. Whatever it was, it's not going to also get carried out on the Ethernet side. For most functional addresses, this isn't an issue. The well-known ones are used for purposes such as: Sending to the active monitor (which doesn't exist on Ethernet) Sending to the ring parameter server (which doesn't exist on Ethernet) Sending to LAN manager (which doesn't exist on Ethernet) etc. You get the picture This particular address is one that I don't recognize though. It may be used for a proprietary (non-standard) function on the Token Ring side. Perhaps you are expected to know these sorts of things to answer this question correctly. Priscilla > How >would the MAC address be interpreted in an Ethernet environment? > >does anyone know the answer? thank you. > >Ivan ________________________ Priscilla Oppenheimer http://www.priscilla.com Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=44849&t=44805 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
