You are absolutely right. It didn't occur to me. It seemed to me that one would have to go out of their way to create a loop in a hub environment. Then after reading your response, I realized I encountered something like this just a few months ago. 2 dual homed Citrix servers using 2 logical subnets but sharing the same physical network. The end user had enabled forwarding between the nics on one of the servers. Guess what the problem was?
Jay -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]] Sent: Monday, December 09, 2002 12:10 PM To: [EMAIL PROTECTED] Subject: RE: Dumb question [7:58783] Jay Dunn wrote: > > A "hub" or "repeater" operates at layer 1 and makes no > intelligent > decision about what to forward. A packet enters a port and is > forwarded > out all other active ports on the hub. The concept of a loop > only exists > at higher layers. A loop could exist at the physical layer too. A newbie could connect the hubs in such a way that there was a loop. And it could indeed cause problems due to the fact that a hub doesn't make any intelligent decisions about what it forwards, as you say, and doesn't participate in higher-layer loop-avoidance solutions such as STP, Dijkstra, split horizon, etc. There would be nothing to stop the looping bits. The very idea makes me cringe. :-) It's kind of funny that nobody thinks about this. A network of hubs must be designed in a hierarchical fashion. I guess that is just second-nature to people who grew up with hubs. When hubs entered the market they allowed us to move away from the ubiquitous bus topology and into a star (hub-and-spoke) topology. They allowed us to start using the structured cabling that AT&T and other vendors were starting to install, rather than the Christmas-tree-lights topology so popular with coax cable and so prone to problems. As networks grew, it became necessary to connect multiple hubs. The term that was often used was "cascating hubs." Hubs cascaed from other hubs, within the rules related to Ethernet propagation delay and collision detection. Priscilla > > Jay Dunn > IPI*GrammTech, Ltd. > www.ipi-gt.com > Nunquam Facilis Est > > -----Original Message----- > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]] On > Behalf Of > Han Chuan Alex Ang > Sent: Monday, December 09, 2002 3:44 AM > To: [EMAIL PROTECTED] > Subject: Dumb question [7:58783] > > I am wondering if Hub could be subjected to loop problems , if > not, what > will happen if there is a loop within a Hub enviroment Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=58868&t=58783 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
