Hi Peter, In a simpler analogy..... vlan 7 would be a seperate switch with a connection to the vlan 1 switch... vlan 8 would be a seperate switch with a connection to the vlan 1 switch..
no loop exist between any part of the 3 networks....vlan 7 and 8 are isolated from each other. So stp sees no loops between vlan 1 and either of the other vlans. if the switches are capable, do a show spantree summ, and see what it replies with.... Peter van Oene wrote: >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=58166&t=58099 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
