At 11:35 AM 4/22/02, Phil Barker wrote: >2. In order to run the spanning tree protocol the >switch needs to send multicast packets out any of its >ports (BPDUs'). >These BPDU's need a source MAC address to distinguish >themselves from each other. > >1. I think the 1024 MAC Addresses is referring to how >many MAC Addresses it could store in memory for the >purpose of switching/bridging. > >i.e once 1024 MAC addresses have been learned it would >not add any others to the table since the memory would >be exhausted.
Phil, Your answer makes sense, but remember this is Cisco we're talking about! ;-) The link says "The supervisor engine has a pool of 1024 MAC addresses that are used as the bridge IDs for the VLAN spanning trees." The link is referring to the switch's own MAC addresses, not the ones in its bridging table. The switch has so many MAC addresses because Cisco supports one spanning tree per VLAN. There's a different bridge ID for each VLAN. Your are right, of course, that a bridge has a bridging table that stores the MAC addresses and port numbers for stations outside the bridge that the bridge has learned about. This is also sometimes called the MAC address table or content addressable memory (CAM). The Cisco Catalyst 1900 (low-end) switch can remember 1024 MAC addresses. A high-end switch such as the Catalyst 6000 can remember 32,000 MAC addresses. You are also right that the source address in a BPDU message is the MAC address of the port on the bridge that is transmitting the message. (The IEEE requires a bridge to have a distinct MAC address for each port.) A bridge also has a Bridge ID, as mentioned. The low-order subfield of a Bridge ID is a 6-byte MAC address assigned to the bridge. This is a hard-coded number that is not designed to be changed by the user. Some Cisco switches use one of the MAC addresses of the switch supervisor module for the Bridge ID, whereas other Cisco switches use a MAC address assigned to the backplane of the switch. Priscilla >Phil. > > > --- Tony Chen wrote: > >Please help a curious mind here, the link is to a > > white paper describing how > > to configuring spanning tree. In the document it > > describes each switch has > > 1024 mac address. > > > > Configuring spanning tree > > > > >http://www.cisco.com/univercd/cc/td/doc/product/lan/cat5000/rel_5_2/config/spantree.htm#xtocid2879613 > > > > MAC Address Allocation > > The supervisor engine has a pool of 1024 MAC > > addresses that are used as the > > bridge IDs for the VLAN spanning trees. You can use > > the show module command > > to view the MAC address range for the supervisor > > engine. > > > > > > > > Each switch has 1024(MAC)addresses. If I connected > > port 8 switch A to port 8 switch B with RJ45 > > crossover > > cable. > > > > 1. Will I have 2048 MAC addresses? > > 2. Do Ethernet switch come with their own MAC > > address? > > > > > > Tony > > > > > > >*********************************************************************** > > This message is a private communication. If you are > > not the intended > > recipient, please do not read, copy, or use it, and > > do not disclose it > > to others. Please notify the sender of the delivery > > error by replying > > to this message, and then delete it from your > > system. Thank you. > > > > > > >--------------------------------------------------------------------- > > Visit http://www.ballfoundation.org for our latest > > news. >[EMAIL PROTECTED] > >__________________________________________________ >Do You Yahoo!? >Everything you'll ever need on one web page >from News and Sport to Email and Music Charts >http://uk.my.yahoo.com ________________________ Priscilla Oppenheimer http://www.priscilla.com Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=42251&t=42226 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
