At 10:41 PM 11/26/2002 +0000, Larry Letterman wrote: >switch A and B wont talk to each other or cause a loop >because you have switch B isolated. STP in your case is >set for 3 instances : STP for Vlan 1, Vlan 7 and Vlan 8. >A loop would be present if switch B were set for Vlan 7 >on both links and STP did not block one of the ports.
I'm curious here. Given Switch A and B don't emit tagged frames, traffic should flow freely despite A and B's disagreement on VLAN ID. I am not very familiar with Per VLAN STP encoding however. Are the BPDU's modified to carry a VLAN identifier? This would seem superfluous to me and I'd wonder where it would be needed. My take on 802.1q PVST+ is that only the common STP BDPUs are sent untagged and all other BPDUs are sent tagged with their appropriate VLAN making them easy to disambiguate. >pauldongso wrote: > > >Hi All, > > > >Please advise how STP participates in the following scenario and why STP > >fails to stop the loop? > > -------------------- > > |switch A | > > --------------------- > > |(vlan 7) | (vlan 8) > > | | > > | | > > |(vlan 1) |(vlan 1) > > ------------------- > > | switch B | > > -------------------- > > | | | > > vlan 1 hosts > > > > > >In short, switch A has two ports configured with vlan 7, vlan 8 > >respectively. Swtich B all ports are at default vlan 1. > >links between swA and swB are access mode. > > > >This scenario creates bridging loop. But just can't figure out why STP > >fails to stop loop. > > > >Thanks in advance. > > > >Paul Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=58158&t=58099 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
