Re: question regarding spanning tree [7:6485]
Hi Heather, In fact the STA, regarding which ports are in forwarding or blocking state, works as follow: 1. Lowest Path Cost 2. Lowest Designated Bridge ID (MAC address + Priority) 3. Lowest port ID That is, imagine that bridge A is running STA to decide wich ports should forward and wich ports should block traffic. If bridge A is receiveing BPDUs on two ports, it will choose the port that is receiving BPDUs announcing the lowest Path Cost. In case of a tie, the port that will be in forwarding state will be the one that is reiceiveing BPDUs in which the Bridge ID is the lowest. If there is a tie at this stage (which happens when the designated bridge is the same bridge in both ports) the lowest port ID from the designated bridge acts as the tie breaker. This is what is happening in your lab. Your 4006 is bridge A and the 6509 is the designated bridge which is connected to the 4006 by two links. Because the 6509's port that is connected to the 4006's port 1/2 has a lower port ID (0x8087)than the 6509's port that connects to the 4006's port 1/1, the 4006 switch will put port 1/2 in forwarding state. I hope this helps. I appologize for my (portuguese)english. Regards, Nuno Morais From: Buri, Heather H Reply-To: Buri, Heather H To: [EMAIL PROTECTED] Subject: question regarding spanning tree [7:6485] Date: Wed, 30 May 2001 13:20:07 -0400 Hello. I don't really have a problem so much as I am trying to get a better understanding of how Spanning Tree works. I am currently studying for my switching exam and am reviewing Spanning Tree. I have the following statement from the Cisco course manual and in the case of redundant paths to the root bridge, it states In order to choose which port will be forwarding data and which ports will be blocking data, the switch looks at two components in the BPDU, as follows: 1. Path Cost 2. Port ID The switch looks at the path cost first to determine which port is receiving the lowest cost path. If the path cost is equal, as in the case of parallel links, the bridge goes to the port ID as a tie-breaker. The port with the lowest port ID forwards and all other ports block. I decided to verify this on one of my 4006's which connects to my 6509 (which is the root) and here is what I found: pet4006_8 (enable) sh spantree statistics 1/2 1 Port 1/2 VLAN 1 SpanningTree enabled for vlanNo = 1 BPDU-related parameters port spanning tree enabled stateforwarding port_id 0x8002 port number 0x2 path cost4 message age (port/VLAN) 0(20) designated_root 00-d0-01-98-5c-00 designated_cost 0 designated_bridge00-d0-01-98-5c-00 designated_port 0x8087 top_change_ack FALSE config_pending FALSE port_inconsistency none PORT based information statistics config bpdu's xmitted (port/VLAN)0(8702816) config bpdu's received (port/VLAN) 831061(1662121) tcn bpdu's xmitted (port/VLAN) 1(1) pet4006_8 (enable) sh spantree statistics 1/1 1 Port 1/1 VLAN 1 SpanningTree enabled for vlanNo = 1 BPDU-related parameters port spanning tree enabled stateblocking port_id 0x8001 port number 0x1 path cost4 message age (port/VLAN) 1(20) designated_root 00-d0-01-98-5c-00 designated_cost 0 designated_bridge00-d0-01-98-5c-00 designated_port 0x80c8 top_change_ack FALSE config_pending FALSE port_inconsistency none However, as you can see from the above output, Port 1/2 is the port chosen to forward and it appears to have a higher port ID number. Can someone please explain what I am missing here? Thanks! Heather Buri CSC Technology Services - Houston Phone: (713)-961-8592 Fax: (713)-961-8249 Mobile: Alpha Page: Mailing: 1360 Post Oak Blvd Suite 500 Houston, TX 77056 EOM NOTICE - This message contains information intended only for the use of the addressee named above. It may also be confidential and/or privileged. If you are not the intended recipient of this message you are hereby notified that you must not disseminate, copy or take any action in reliance on it. If you have received this message in error please notify [EMAIL PROTECTED] FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] _ Get Your Private, Free E-mail from MSN
RE: question regarding spanning tree [7:6485]
Heather, Its the received port id You should find that port 1/2 is connected to the 6509 on a lower port than port 1/1 do a sh cdp neigh to confirm Hope this is correct -Paul -Original Message- From: Buri, Heather H [mailto:[EMAIL PROTECTED]] Sent: 30 May 2001 18:20 To: [EMAIL PROTECTED] Subject: question regarding spanning tree [7:6485] Hello. I don't really have a problem so much as I am trying to get a better understanding of how Spanning Tree works. I am currently studying for my switching exam and am reviewing Spanning Tree. I have the following statement from the Cisco course manual and in the case of redundant paths to the root bridge, it states In order to choose which port will be forwarding data and which ports will be blocking data, the switch looks at two components in the BPDU, as follows: 1. Path Cost 2. Port ID The switch looks at the path cost first to determine which port is receiving the lowest cost path. If the path cost is equal, as in the case of parallel links, the bridge goes to the port ID as a tie-breaker. The port with the lowest port ID forwards and all other ports block. I decided to verify this on one of my 4006's which connects to my 6509 (which is the root) and here is what I found: pet4006_8 (enable) sh spantree statistics 1/2 1 Port 1/2 VLAN 1 SpanningTree enabled for vlanNo = 1 BPDU-related parameters port spanning tree enabled stateforwarding port_id 0x8002 port number 0x2 path cost4 message age (port/VLAN) 0(20) designated_root 00-d0-01-98-5c-00 designated_cost 0 designated_bridge00-d0-01-98-5c-00 designated_port 0x8087 top_change_ack FALSE config_pending FALSE port_inconsistency none PORT based information statistics config bpdu's xmitted (port/VLAN)0(8702816) config bpdu's received (port/VLAN) 831061(1662121) tcn bpdu's xmitted (port/VLAN) 1(1) pet4006_8 (enable) sh spantree statistics 1/1 1 Port 1/1 VLAN 1 SpanningTree enabled for vlanNo = 1 BPDU-related parameters port spanning tree enabled stateblocking port_id 0x8001 port number 0x1 path cost4 message age (port/VLAN) 1(20) designated_root 00-d0-01-98-5c-00 designated_cost 0 designated_bridge00-d0-01-98-5c-00 designated_port 0x80c8 top_change_ack FALSE config_pending FALSE port_inconsistency none However, as you can see from the above output, Port 1/2 is the port chosen to forward and it appears to have a higher port ID number. Can someone please explain what I am missing here? Thanks! Heather Buri CSC Technology Services - Houston Phone: (713)-961-8592 Fax:(713)-961-8249 Mobile: Alpha Page: Mailing:1360 Post Oak Blvd Suite 500 Houston, TX 77056 EOM NOTICE - This message contains information intended only for the use of the addressee named above. It may also be confidential and/or privileged. If you are not the intended recipient of this message you are hereby notified that you must not disseminate, copy or take any action in reliance on it. If you have received this message in error please notify [EMAIL PROTECTED] FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] PLEASE READ: The information contained in this e-mail is confidential and intended for the named recipient(s) only. If you are not an intended recipient of this email you must not copy, distribute or take any further action in reliance on it and you should delete it and notify the sender immediately. Email is not a secure method of communication and Nomura International plc cannot accept responsibility for the accuracy or completeness of this message or any attachment(s). Please examine this e-mail for virus infection, for which Nomura International plc accepts no responsibility. If verification of this email is sought then please request a hard copy. Unless otherwise stated any views or opinions presented are solely those of the author and do not represent those of Nomura International plc. This email is intended for informational purposes only and is not a solicitation or offer to buy or sell securities or related financial instruments. Nomura International plc is regulated by the Securities and Futures Authority Limited and is a member of the London Stock Exchange. Message Posted at:
RE: question regarding spanning tree [7:6485]
Hi Paul, You were right! Thanks for clearing that up for me. I feel kind of silly now because I think I was trying to make it more difficult than it was, but it is nice to know the answer! pet4006_8 (enable) sh cdp neigh * - indicates vlan mismatch. # - indicates duplex mismatch. Port Device-ID Port-ID Platform --- - 1/1 SCA04230312(PETHOU-6509-02) 4/8 WS-C6509 1/2 SCA04230312(PETHOU-6509-02) 3/7 WS-C6509 pet4006_8 (enable) Heather Buri CSC Technology Services - Houston Phone: (713)-961-8592 Fax:(713)-961-8249 Mobile: Alpha Page: Mailing:1360 Post Oak Blvd Suite 500 Houston, TX 77056 -Original Message- From: Williamson, Paul [mailto:[EMAIL PROTECTED]] Sent: Wednesday, May 30, 2001 12:45 PM To: 'Buri, Heather H'; [EMAIL PROTECTED] Subject: RE: question regarding spanning tree [7:6485] Heather, Its the received port id You should find that port 1/2 is connected to the 6509 on a lower port than port 1/1 do a sh cdp neigh to confirm Hope this is correct -Paul -Original Message- From: Buri, Heather H [mailto:[EMAIL PROTECTED]] Sent: 30 May 2001 18:20 To: [EMAIL PROTECTED] Subject: question regarding spanning tree [7:6485] Hello. I don't really have a problem so much as I am trying to get a better understanding of how Spanning Tree works. I am currently studying for my switching exam and am reviewing Spanning Tree. I have the following statement from the Cisco course manual and in the case of redundant paths to the root bridge, it states In order to choose which port will be forwarding data and which ports will be blocking data, the switch looks at two components in the BPDU, as follows: 1. Path Cost 2. Port ID The switch looks at the path cost first to determine which port is receiving the lowest cost path. If the path cost is equal, as in the case of parallel links, the bridge goes to the port ID as a tie-breaker. The port with the lowest port ID forwards and all other ports block. I decided to verify this on one of my 4006's which connects to my 6509 (which is the root) and here is what I found: pet4006_8 (enable) sh spantree statistics 1/2 1 Port 1/2 VLAN 1 SpanningTree enabled for vlanNo = 1 BPDU-related parameters port spanning tree enabled stateforwarding port_id 0x8002 port number 0x2 path cost4 message age (port/VLAN) 0(20) designated_root 00-d0-01-98-5c-00 designated_cost 0 designated_bridge00-d0-01-98-5c-00 designated_port 0x8087 top_change_ack FALSE config_pending FALSE port_inconsistency none PORT based information statistics config bpdu's xmitted (port/VLAN)0(8702816) config bpdu's received (port/VLAN) 831061(1662121) tcn bpdu's xmitted (port/VLAN) 1(1) pet4006_8 (enable) sh spantree statistics 1/1 1 Port 1/1 VLAN 1 SpanningTree enabled for vlanNo = 1 BPDU-related parameters port spanning tree enabled stateblocking port_id 0x8001 port number 0x1 path cost4 message age (port/VLAN) 1(20) designated_root 00-d0-01-98-5c-00 designated_cost 0 designated_bridge00-d0-01-98-5c-00 designated_port 0x80c8 top_change_ack FALSE config_pending FALSE port_inconsistency none However, as you can see from the above output, Port 1/2 is the port chosen to forward and it appears to have a higher port ID number. Can someone please explain what I am missing here? Thanks! Heather Buri CSC Technology Services - Houston Phone: (713)-961-8592 Fax:(713)-961-8249 Mobile: Alpha Page: Mailing:1360 Post Oak Blvd Suite 500 Houston, TX 77056 EOM NOTICE - This message contains information intended only for the use of the addressee named above. It may also be confidential and/or privileged. If you are not the intended recipient of this message you are hereby notified that you must not disseminate, copy or take any action in reliance on it. If you have received this message in error please notify [EMAIL PROTECTED] FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] PLEASE READ
Re: question regarding spanning tree [7:6485]
nope. thats wrong... it's four steps. 1. lowest root BID 2. lowest path cost 3.lowest sending BID 4.Lowest port ID. all of which are contained in a Config BPDU. this is also part of how the root bridge is established... -Peter Slow, CCNP Voice Guy - Original Message - From: Buri, Heather H To: Sent: Wednesday, May 30, 2001 1:20 PM Subject: question regarding spanning tree [7:6485] Hello. I don't really have a problem so much as I am trying to get a better understanding of how Spanning Tree works. I am currently studying for my switching exam and am reviewing Spanning Tree. I have the following statement from the Cisco course manual and in the case of redundant paths to the root bridge, it states In order to choose which port will be forwarding data and which ports will be blocking data, the switch looks at two components in the BPDU, as follows: 1. Path Cost 2. Port ID The switch looks at the path cost first to determine which port is receiving the lowest cost path. If the path cost is equal, as in the case of parallel links, the bridge goes to the port ID as a tie-breaker. The port with the lowest port ID forwards and all other ports block. I decided to verify this on one of my 4006's which connects to my 6509 (which is the root) and here is what I found: pet4006_8 (enable) sh spantree statistics 1/2 1 Port 1/2 VLAN 1 SpanningTree enabled for vlanNo = 1 BPDU-related parameters port spanning tree enabled stateforwarding port_id 0x8002 port number 0x2 path cost4 message age (port/VLAN) 0(20) designated_root 00-d0-01-98-5c-00 designated_cost 0 designated_bridge00-d0-01-98-5c-00 designated_port 0x8087 top_change_ack FALSE config_pending FALSE port_inconsistency none PORT based information statistics config bpdu's xmitted (port/VLAN)0(8702816) config bpdu's received (port/VLAN) 831061(1662121) tcn bpdu's xmitted (port/VLAN) 1(1) pet4006_8 (enable) sh spantree statistics 1/1 1 Port 1/1 VLAN 1 SpanningTree enabled for vlanNo = 1 BPDU-related parameters port spanning tree enabled stateblocking port_id 0x8001 port number 0x1 path cost4 message age (port/VLAN) 1(20) designated_root 00-d0-01-98-5c-00 designated_cost 0 designated_bridge00-d0-01-98-5c-00 designated_port 0x80c8 top_change_ack FALSE config_pending FALSE port_inconsistency none However, as you can see from the above output, Port 1/2 is the port chosen to forward and it appears to have a higher port ID number. Can someone please explain what I am missing here? Thanks! Heather Buri CSC Technology Services - Houston Phone: (713)-961-8592 Fax: (713)-961-8249 Mobile: Alpha Page: Mailing: 1360 Post Oak Blvd Suite 500 Houston, TX 77056 EOM NOTICE - This message contains information intended only for the use of the addressee named above. It may also be confidential and/or privileged. If you are not the intended recipient of this message you are hereby notified that you must not disseminate, copy or take any action in reliance on it. If you have received this message in error please notify [EMAIL PROTECTED] FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] Message Posted at: http://www.groupstudy.com/form/read.php?f=7i=6502t=6485 -- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
