Well, I don't have that book but let me go off went you sent. _______ Assumptions made: All 3 switches carry both VLAN's and all 3 switchs have members in both VLAN's. The links between Switches are setup for VLAN trunking _______
Cat-C will have traffic that needs to access servers in both VLANS. Cat-A would be the root bridge for VLAN2 and all traffic would flow through it for this VLAN. Same for Cat-B and VLAN3.However, lets assume that the link between Cat-C and Cat-A fails. Now Cat-C can't send traffic directly to Cat-A, but It can however send to Cat-B which can send traffic across the link between them to get to Cat-A. Reverse the process for VLAN3. Traffic by default will flow towards the root bridge. That being said Traffic for VLAN 2 will always go across the VLAN2 link to Cat-A because that is the shorts distance to the Root bridge. A secondary route exists to Cat-A, via Cat-B, but since its not the shortest, that ports would be in a blocking mode (1/2 on Cat-C) for VLAN2. Only when Cat-C detects a failure, would a new STP algorithm be run, at which point Cat-C would detect that the shortest route to Cat-A would be through Cat-B. Once that happens traffic for that VLAN would begin going across the VLAN3 link even if it is for VLAN2. Now Cat-C has the same scenario for VLAN3 but this time, the shortest route to the Root Bridge for VLAN3 is across the VLAN3 link and the path (port 1/1) would be in a blocking mode for VLAN3. For this to work, the link between Cat-B and Cat-C would need to be a trunk port that carries VLAN2&3. This would provide the failover path for the VLAN's in the event of a link failure between Cat-C and one of the other Cat switches. In the case of a failure of either Cat-B or C, your out of luck for those servers connected to it. I suggest A quick call to TAC ! What I think might be confusing you ( if I haven't!) is that your thinking that if someone on Cat-C needs access to a server in VLAN2 that is physically plugged into Cat-B you might think that traffic would go across the link from Cat-C to Cat-B. Well, it doesn't, it would go from Cat-C to Cat-A to Cat-B. Ok, portion 2. Techically this is load sharing not load balancing BTW. Lets also assume that 2 servers plugged into Cat-A are hogging the BW. One server(SRV2) is in VLAN2 and the other is in VLAN3(SRV3). The traffic for SRV2 would go from Cat-C out port 1/1 directly to Cat-A. The traffic for SRV3 however would go out port 1/2 on Cat-C to Cat-B then from Cat-B across the link to Cat-A. If all links are 100Mbs, both servers would have a dedicated 100Mbs of BW to Cat-C,since each follows a different path to Cat-C. Hope I have not confused you any. I have retyped about 3 times trying to simply but point out the important parts. If you would like me to clear anything up let me know. Hope it helps. Thanks Larry -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]] Sent: Saturday, June 15, 2002 9:16 PM To: [EMAIL PROTECTED] Subject: STP Question: Root Bridge placement load balancing [7:46701] Hi, Studying Cisco LAN Switching,(by Hamilton & Clark), I didn't get how exactly this method (Root Bridge placement load balancing)works. He provides such an example (Figure 7-10): ___________ |Cat-C (IDF)| |___________| 1/1 / \ 1/2 / \ VLAN2 / \ VLAN3 / \ / \ 1/1 / \ 1/1 ______/___ _\________ |Cat-A(MDF)|__________|Cat-B(MDF)| |__________|1/2 1/2|__________| | | | | Server Farm Server Farm Assuming that CAT-A is the Root bridge for VLAN2 and CAT-B is the Root bridge for VLAN 3, I don't get how this method provides load balancing and redundancy for CAT-C to the server farms. He doen't say anything about the third segment (the segment between CAT-A and CAT-B) Could anyone clearify please ? Thanks in advance, Hamid Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=46703&t=46703 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
