At 06:45 PM 2/26/02, Pierre-Alex wrote: >Question (1) > >Is the first part of this statement correct? > >I have looked at the 801d paper for an answer but I am still uncertain.
The IEEE 802.1D document is tough to read. Try the Cisco LAN Switching book by Clark and Hamilton. It's a masterpiece. >"In blocking mode, an interface will receive and send BPDUs but not send >and receive data traffic. " In blocking mode, an interface receives and processes BPDUs. It doesn't send them. It also does not forward data traffic. >Question (2) > >Are blocked port considered part of the spanning tree? Of course not. What would be the point? >When I do a "show span" on switches, It's showing you info about the spanning tree process, not the tree. From my new book (copyrighted by me, and please don't copy without giving me credit ;-) A tree is more than just a woody perennial plant with few limbs on its lower part. A tree is also a mathematical concept. A tree is a diagram or graph that branches from a single stem without forming loops or polygons. A computer network is usually not physically constructed as a tree because of the requirements to provide redundancy and avoid any single points of failure. STP prunes the physical topology of a bridged network into a logical tree topology. Topology is more than just a word that Cisco and other vendors throw around when discussing network design. Topology is a branch of mathematics concerned with those properties of geometric configurations which are unaltered by elastic deformations such as stretching or twisting. (For example, did you know that according to topology principles, a donut is the same shape as a coffee cup? Think about it!) To understand a tree topology, think about a document outline, a table of contents, a hierarchical org chart, cluster diagrams used in brainstorming, and genealogy charts. These are all trees. Unless brothers and sisters or cousins marry, (which does happen sometimes), there is a single path between any two people in a genealogical tree. In a bridged or switched computer network, STP ensures that there is a single path between LANs. STP allows bridges to discover a loop-free, tree-shaped subset of the physical topology that spans the bridged network. In other words, STP produces a spanning tree. NOTE: With networking, as with mathematics, the tree is usually drawn upside down. The root is placed at the top of the drawing. >I do see the blocked port listed >but on testing material I have seen both answers: one reference says >blocked ports are part of the spanning tree another says they are not. > >Which one is true? > >Question (3) > >What is the difference between a BPDU and a Configuration BPDU? Is it >right to say that configuration BPDUs are sent only by the root bridge >and that BPDUs are fowarded by non-root bridges? BPDU is a protocol. There are two types of messages: Configuration BPDUs and Topology Change Notification BPDUs Once the logical tree has been formed, BPDU traffic continues endlessly. The Root Bridge sends configuration BPDUs out all its ports every Hello Timer interval, which is every two seconds by default. Configuration BPDUs arrive at the Root Ports on bridges downstream from the root. These bridges send configuration BPDUs on their Designated Ports. Topology Change Notification BPDUs happen when there's a change. They travel upstream. Read up on how the protocol behaves. You'll need to know it and it's very interesting. Good luck, Priscilla > >Thanks a lot, > >Pierre-Alex ________________________ Priscilla Oppenheimer http://www.priscilla.com Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=36579&t=36559 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
