BCMSN: STP topology changes
Ole- When the root switch sends out the topology change BPDU, it does not specify that Switch E is no longer available. It simply flips the Topology Change bit in every Configuration BPDU saying that there has been a topology change SOMEWHERE. This lets the switches age out entries in Forward Delay seconds, 15 by default, much faster than the default 300 seconds. It sends these TC BPDUs out for Forward Delay + Max Age seconds (a default of 35 seconds). Once this time is up, it stops flipping the TC bit in the configuration BPDUs. The Cisco Press book by Clark/Hamilton, Cisco LAN Switching has two chapters on STP that are undeniably the best around. Its worth reading if you're taking BCMSN. /Jared -Original Message- From: Ole Drews Jensen [mailto:[EMAIL PROTECTED]] Sent: Sunday, September 10, 2000 10:35 AM To: '[EMAIL PROTECTED]' Subject: BCMSN: STP topology changes I am not sure if it's me running on 50% power this Sunday morning (most likely), if it's the book that is written like a white house speech, or if it's both. Anyway, the reason for this e-mail is that I am reading something that to me doesn't make sense. For those of you who would like to comment on this, if you have Cisco Press' BCMSN book, I am refereing to "Handling Topology Changes in Spanning Tree" on pages 142 and 143. If you do not have that book, here's a quick description: Switch A is the ROOT bridge. Switch B and C are both connected to Switch A. Switch D is connected to both Switch B and C. Switch E is connected to Switch D. Since A and D can see each other through both Switch B and C, the connection between D and C is blocked. The situation is that Switch D's link to E fails, and Switch D sends a notice to Switch A (the root bridge) via Switch B. The root bridge (Switch A) now sets the topology change in its configuration for a period of time equal to the sum of the fwd delay and max age parameters. According to step 5 (in the book): "A bridge receiving the topology change configuration message from the root bridge uses the fwd delay timer to age out entries in its address table. This allows it to age out entries faster than the normal five-minute default so that stations that are no longer available due to the topology change will be aged out faster. It does this until it no longer receives topology change configuration messages from the root bridge." The last line in that quote makes it sound like it keeps receiving messages about the link E being down until it's up again - but what if the Switch E never comes up again because it was sold to someone else - will the root bridge keep sending messages about it forever??? - I don't think so, but that is how I read it. Can someone please clarify this for me? Thanks in advance, Ole Ole Drews Jensen Systems Network Manager CCNA, MCSE, MCP+I RWR Enterprises, Inc. [EMAIL PROTECTED] http://www.insync.net/~drews/ccnp **NOTE: New CCNA/CCDA List has been formed. For more information go to http://www.groupstudy.com/list/Associates.html _ UPDATED Posting Guidelines: http://www.groupstudy.com/list/guide.html FAQ, list archives, and subscription info: http://www.groupstudy.com Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] **NOTE: New CCNA/CCDA List has been formed. For more information go to http://www.groupstudy.com/list/Associates.html _ UPDATED Posting Guidelines: http://www.groupstudy.com/list/guide.html FAQ, list archives, and subscription info: http://www.groupstudy.com Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: BCMSN: STP topology changes
Thanks Jared, that was a good explanation. I have yet a little more that 50% of the book left to read, but if I do not feel secure about STP (and other BCMSN related stuff) when I'm done, I will surely consider buying the Cisco LAN Switching book. Take care, Ole Ole Drews Jensen Systems Network Manager CCNA, MCSE, MCP+I RWR Enterprises, Inc. [EMAIL PROTECTED] http://www.insync.net/~drews/ccnp -Original Message- From: Jared Carter [mailto:[EMAIL PROTECTED]] Sent: Sunday, September 10, 2000 12:45 PM To: [EMAIL PROTECTED]; [EMAIL PROTECTED] Subject: BCMSN: STP topology changes Ole- When the root switch sends out the topology change BPDU, it does not specify that Switch E is no longer available. It simply flips the Topology Change bit in every Configuration BPDU saying that there has been a topology change SOMEWHERE. This lets the switches age out entries in Forward Delay seconds, 15 by default, much faster than the default 300 seconds. It sends these TC BPDUs out for Forward Delay + Max Age seconds (a default of 35 seconds). Once this time is up, it stops flipping the TC bit in the configuration BPDUs. The Cisco Press book by Clark/Hamilton, Cisco LAN Switching has two chapters on STP that are undeniably the best around. Its worth reading if you're taking BCMSN. /Jared -Original Message- From: Ole Drews Jensen [mailto:[EMAIL PROTECTED]] Sent: Sunday, September 10, 2000 10:35 AM To: '[EMAIL PROTECTED]' Subject: BCMSN: STP topology changes I am not sure if it's me running on 50% power this Sunday morning (most likely), if it's the book that is written like a white house speech, or if it's both. Anyway, the reason for this e-mail is that I am reading something that to me doesn't make sense. For those of you who would like to comment on this, if you have Cisco Press' BCMSN book, I am refereing to "Handling Topology Changes in Spanning Tree" on pages 142 and 143. If you do not have that book, here's a quick description: Switch A is the ROOT bridge. Switch B and C are both connected to Switch A. Switch D is connected to both Switch B and C. Switch E is connected to Switch D. Since A and D can see each other through both Switch B and C, the connection between D and C is blocked. The situation is that Switch D's link to E fails, and Switch D sends a notice to Switch A (the root bridge) via Switch B. The root bridge (Switch A) now sets the topology change in its configuration for a period of time equal to the sum of the fwd delay and max age parameters. According to step 5 (in the book): "A bridge receiving the topology change configuration message from the root bridge uses the fwd delay timer to age out entries in its address table. This allows it to age out entries faster than the normal five-minute default so that stations that are no longer available due to the topology change will be aged out faster. It does this until it no longer receives topology change configuration messages from the root bridge." The last line in that quote makes it sound like it keeps receiving messages about the link E being down until it's up again - but what if the Switch E never comes up again because it was sold to someone else - will the root bridge keep sending messages about it forever??? - I don't think so, but that is how I read it. Can someone please clarify this for me? Thanks in advance, Ole Ole Drews Jensen Systems Network Manager CCNA, MCSE, MCP+I RWR Enterprises, Inc. [EMAIL PROTECTED] http://www.insync.net/~drews/ccnp **NOTE: New CCNA/CCDA List has been formed. For more information go to http://www.groupstudy.com/list/Associates.html _ UPDATED Posting Guidelines: http://www.groupstudy.com/list/guide.html FAQ, list archives, and subscription info: http://www.groupstudy.com Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] **NOTE: New CCNA/CCDA List has been formed. For more information go to http://www.groupstudy.com/list/Associates.html _ UPDATED Posting Guidelines: http://www.groupstudy.com/list/guide.html FAQ, list archives, and subscription info: http://www.groupstudy.com Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
RE: BCMSN: STP topology changes
Thanks Daniel, That's what I had thought and hoped for - I just felt that the way it was written made it sound like it just kept on notifying other switches. I am currently creating a "good-old-dos" application in Turbo Pascal 5.5 that will simulate a set-command based switch. It is not a true simulator (yet) since it will only tell you if your command was good or not, and what the result of the command would be. Anyway, I am putting in the commands as I read them in the book - that way I can practise them on the way. When I'm done with it, and if it turns out to be any good - I will make it available for free at my website. May the rest of your weekend be great, Ole Ole Drews Jensen Systems Network Manager CCNA, MCSE, MCP+I RWR Enterprises, Inc. [EMAIL PROTECTED] http://www.insync.net/~drews/ccnp -Original Message- From: Daniel Boutet [mailto:[EMAIL PROTECTED]] Sent: Sunday, September 10, 2000 11:14 AM To: [EMAIL PROTECTED] Subject: Re: BCMSN: STP topology changes Ole I am not 100% sure but I think that you forgot that it is only meant to age out the entry faster that the default value of 300 sec or 5 minutes. There are also the Hello msg that tells a switch which port is actually "live". If you read a little further on page 159 there is mention of timers for bpdu lifetime. Hope this helps to clarify. "Ole Drews Jensen" <[EMAIL PROTECTED]> wrote in message 2019FB428FD3D311893700508B71EBFB2C5B6E@RWR_MAIL_SVR">news:2019FB428FD3D311893700508B71EBFB2C5B6E@RWR_MAIL_SVR... > I am not sure if it's me running on 50% power this Sunday morning (most > likely), if it's the book that is written like a white house speech, or if > it's both. Anyway, the reason for this e-mail is that I am reading something > that to me doesn't make sense. > > For those of you who would like to comment on this, if you have Cisco Press' > BCMSN book, I am refereing to "Handling Topology Changes in Spanning Tree" > on pages 142 and 143. > > If you do not have that book, here's a quick description: > > Switch A is the ROOT bridge. > > Switch B and C are both connected to Switch A. > > Switch D is connected to both Switch B and C. > > Switch E is connected to Switch D. > > Since A and D can see each other through both Switch B and C, the connection > between D and C is blocked. > > The situation is that Switch D's link to E fails, and Switch D sends a > notice to Switch A (the root bridge) via Switch B. > > The root bridge (Switch A) now sets the topology change in its configuration > for a period of time equal to the sum of the fwd delay and max age > parameters. > > According to step 5 (in the book): "A bridge receiving the topology change > configuration message from the root bridge uses the fwd delay timer to age > out entries in its address table. This allows it to age out entries faster > than the normal five-minute default so that stations that are no longer > available due to the topology change will be aged out faster. It does this > until it no longer receives topology change configuration messages from the > root bridge." > > The last line in that quote makes it sound like it keeps receiving messages > about the link E being down until it's up again - but what if the Switch E > never comes up again because it was sold to someone else - will the root > bridge keep sending messages about it forever??? - I don't think so, but > that is how I read it. > > Can someone please clarify this for me? > > Thanks in advance, > > Ole > > > Ole Drews Jensen > Systems Network Manager > CCNA, MCSE, MCP+I > RWR Enterprises, Inc. > [EMAIL PROTECTED] > http://www.insync.net/~drews/ccnp > > > > **NOTE: New CCNA/CCDA List has been formed. For more information go to > http://www.groupstudy.com/list/Associates.html > _ > UPDATED Posting Guidelines: http://www.groupstudy.com/list/guide.html > FAQ, list archives, and subscription info: http://www.groupstudy.com > Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] > **NOTE: New CCNA/CCDA List has been formed. For more information go to http://www.groupstudy.com/list/Associates.html _ UPDATED Posting Guidelines: http://www.groupstudy.com/list/guide.html FAQ, list archives, and subscription info: http://www.groupstudy.com Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] **NOTE: New CCNA/CCDA List has been formed. For more information go to http://www.groupstudy.com/list/Associates.html _ UPDATED Posting Guidelines: http://www.groupstudy.com/list/guide.html FAQ, list archives, and subscription info: http://www.groupstudy.com Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
Re: BCMSN: STP topology changes
Ole I am not 100% sure but I think that you forgot that it is only meant to age out the entry faster that the default value of 300 sec or 5 minutes. There are also the Hello msg that tells a switch which port is actually "live". If you read a little further on page 159 there is mention of timers for bpdu lifetime. Hope this helps to clarify. "Ole Drews Jensen" <[EMAIL PROTECTED]> wrote in message 2019FB428FD3D311893700508B71EBFB2C5B6E@RWR_MAIL_SVR">news:2019FB428FD3D311893700508B71EBFB2C5B6E@RWR_MAIL_SVR... > I am not sure if it's me running on 50% power this Sunday morning (most > likely), if it's the book that is written like a white house speech, or if > it's both. Anyway, the reason for this e-mail is that I am reading something > that to me doesn't make sense. > > For those of you who would like to comment on this, if you have Cisco Press' > BCMSN book, I am refereing to "Handling Topology Changes in Spanning Tree" > on pages 142 and 143. > > If you do not have that book, here's a quick description: > > Switch A is the ROOT bridge. > > Switch B and C are both connected to Switch A. > > Switch D is connected to both Switch B and C. > > Switch E is connected to Switch D. > > Since A and D can see each other through both Switch B and C, the connection > between D and C is blocked. > > The situation is that Switch D's link to E fails, and Switch D sends a > notice to Switch A (the root bridge) via Switch B. > > The root bridge (Switch A) now sets the topology change in its configuration > for a period of time equal to the sum of the fwd delay and max age > parameters. > > According to step 5 (in the book): "A bridge receiving the topology change > configuration message from the root bridge uses the fwd delay timer to age > out entries in its address table. This allows it to age out entries faster > than the normal five-minute default so that stations that are no longer > available due to the topology change will be aged out faster. It does this > until it no longer receives topology change configuration messages from the > root bridge." > > The last line in that quote makes it sound like it keeps receiving messages > about the link E being down until it's up again - but what if the Switch E > never comes up again because it was sold to someone else - will the root > bridge keep sending messages about it forever??? - I don't think so, but > that is how I read it. > > Can someone please clarify this for me? > > Thanks in advance, > > Ole > > > Ole Drews Jensen > Systems Network Manager > CCNA, MCSE, MCP+I > RWR Enterprises, Inc. > [EMAIL PROTECTED] > http://www.insync.net/~drews/ccnp > > > > **NOTE: New CCNA/CCDA List has been formed. For more information go to > http://www.groupstudy.com/list/Associates.html > _ > UPDATED Posting Guidelines: http://www.groupstudy.com/list/guide.html > FAQ, list archives, and subscription info: http://www.groupstudy.com > Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] > **NOTE: New CCNA/CCDA List has been formed. For more information go to http://www.groupstudy.com/list/Associates.html _ UPDATED Posting Guidelines: http://www.groupstudy.com/list/guide.html FAQ, list archives, and subscription info: http://www.groupstudy.com Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
BCMSN: STP topology changes
I am not sure if it's me running on 50% power this Sunday morning (most likely), if it's the book that is written like a white house speech, or if it's both. Anyway, the reason for this e-mail is that I am reading something that to me doesn't make sense. For those of you who would like to comment on this, if you have Cisco Press' BCMSN book, I am refereing to "Handling Topology Changes in Spanning Tree" on pages 142 and 143. If you do not have that book, here's a quick description: Switch A is the ROOT bridge. Switch B and C are both connected to Switch A. Switch D is connected to both Switch B and C. Switch E is connected to Switch D. Since A and D can see each other through both Switch B and C, the connection between D and C is blocked. The situation is that Switch D's link to E fails, and Switch D sends a notice to Switch A (the root bridge) via Switch B. The root bridge (Switch A) now sets the topology change in its configuration for a period of time equal to the sum of the fwd delay and max age parameters. According to step 5 (in the book): "A bridge receiving the topology change configuration message from the root bridge uses the fwd delay timer to age out entries in its address table. This allows it to age out entries faster than the normal five-minute default so that stations that are no longer available due to the topology change will be aged out faster. It does this until it no longer receives topology change configuration messages from the root bridge." The last line in that quote makes it sound like it keeps receiving messages about the link E being down until it's up again - but what if the Switch E never comes up again because it was sold to someone else - will the root bridge keep sending messages about it forever??? - I don't think so, but that is how I read it. Can someone please clarify this for me? Thanks in advance, Ole Ole Drews Jensen Systems Network Manager CCNA, MCSE, MCP+I RWR Enterprises, Inc. [EMAIL PROTECTED] http://www.insync.net/~drews/ccnp **NOTE: New CCNA/CCDA List has been formed. For more information go to http://www.groupstudy.com/list/Associates.html _ UPDATED Posting Guidelines: http://www.groupstudy.com/list/guide.html FAQ, list archives, and subscription info: http://www.groupstudy.com Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
