I used to wonder why I had such a hard time grasping technology concepts until I reached a level where I actually understood some of this stuff. Then I found that a lot of sources either did not understand the concepts themselves or worse yet, they were so imprecise with their language and terminology, that they created confusion in the mind of the newbie learner. Some comments below:
""Kevin Jones"" wrote in message [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > Ok. I found the source of the information. I would like to here your > feedback on this. > > Course Technology * Thompson Learning, i-Net+ Guide to Internet > Technologies, Jean Andrews, p. 443-445 > > "What is the difference between a bridge and a switch? The main difference > is how they work. A bridge broadcasts data to one or more LANs while a > switch knows which LAN a packet should be sent to." ????? since both are layer 2 devices, and layer two has no concept of "LAN" let alone "different LAN's" what does this mean? > > "In order to determine which network the packet should be sent to, the > bridge creates and maintains a routing table that lists the computers on The use of the term "routing table" is inaacurate. layer two does not "route" I believe the proper term is "forwarding base", which is more generic, and more proper. > each LAN. A separate table is kept for each LAN. ?????????? not on any bridge or switch I've ever worked with >When a data packet > reaches the bridge, the bridge looks at the packet's destination address, > then searches the routing table for the originating LAN, looking for the > destination address of the data packet. If it finds the address in this > routing table, it drops the packet, knowing that the packet will have > already reached its destination, because it was broadcast to all nodes on > the LAN by the LAN's hub." sigh......... totally wrong in concept and in explaination....... > > "If the bridge did not find the destination address in the routing table for > that LAN, it broadcasts the packet to all nodes on all LANs it is connected > to except the LAN that the packet came from. Therefore, a bridge only makes > a single decision, 'Is this packet destined for a node on its own network?' > If the answer is 'No,', then the bridge simply broadcasts it to all other > LANs." ??????..... I think I begin to understand what the author is intending. The author appears to be saying that each port on a bridge is associated with a LAN. This can be considered conceptually correct in a manner of speaking, but again, the imprecision of terminology is causing confusion...... > > "A switch, on the other hand, deosn not work by sending broadcast messages. > Just like bridges, switches also keep tables of all the MAC addresses of all > the devices connected to the switch. They use these tables to determine > which path to use when sending packets." here we go,,, the author now gets into the correct concept - MAC addresses - which bridges use also. > > "... Using the destination address in the header of the packet, the switch > would refer to its tables and determine the LAN to which the packet is > addressed. The switch then forwards the packet to the proper LAN, rather > than broadcasting the packet to all the LANs." the author continues to confuse L2 and L3 terminaology. L2 is "frame" - recall your CCNA materials..... > > From this thread, and from past experience, shall we assume that this is > completely false? While i-Net plus only skims the surface of network > technology, this book (like many others) seems to have a lot of errors. > Another example would be the fact that the MAC tables are referred to as > routing tables. no kidding there are errors. just goes to show > > That reminds me, what is the difference between a MAC table and a CAM table? Cisco calls the mac table a "content addressable memory" table. without spending more time than I have at the moment, I can't find a history on CCO as to why they do this. > > Kevin Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=44960&t=44649 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
