I've read that the initial 20 second "blocking" delay is only on true port initialization, like after power-up, and not just when a port goes from 'notconnect' to 'connected.' It's there so the switch listens to BPDUs for a bit longer after initial boot before starting to participate in STP.
For a normal port-up scenario I think you only have listen/learn delays, and you also have the max-age timer in event of an indirect change scenario where the port stops hearing BPDUs. Here is an excerpt of a Cisco Press book that describes my understanding: http://www.informit.com/library/content.aspx?b=CCNP_Studies_Switching&seqNum=29 Specifically: A port is disabled when the Layer 2 protocol is down on the port, whether it be because the port has been administratively shut down, because it is not connected, or because of some issue with processing BPDUs. A port transitions from the Disabled state to the Blocking state and then * immediately* to a Listening state after it is initialized at the Layer 2 level. This seems to agree with the empirical results that frequently get reported on this list and on blogs. Sent from my iPad On Nov 30, 2011, at 2:17 AM, "Di Bias, Steve" <[email protected]> wrote: Yup I agree and here were my test results from that thread: First when bringing up a port that doesn't have any portfast configuration the blocking state was still less than 1 second (there was no 20 second blocking) interface GigabitEthernet1/0/19 shutdown end Switch(config)#int g1/0/19 Switch(config-if)#no shut *Mar 1 00:15:29.080: %LINK-3-UPDOWN: Interface GigabitEthernet1/0/19, changed state to down *Mar 1 00:15:29.625: setting bridge id (which=3) prio 32769 prio cfg 32768 sysid 1 (on) id 8001.0023.ab49.6e00 *Mar 1 00:15:29.625: set portid: VLAN0001 Gi1/0/19: new port id 8013 *Mar 1 00:15:29.625: STP: VLAN0001 Gi1/0/19 -> listening *Mar 1 00:15:31.345: STP: VLAN0001 heard root 32769-001e.f692.a000 on Gi1/0/19 *Mar 1 00:15:31.345: supersedes 32769-0023.ab49.6e00 *Mar 1 00:15:31.345: STP: VLAN0001 new root is 32769, 001e.f692.a000 on port Gi1/0/19, cost 4 *Mar 1 00:15:31.622: %LINK-3-UPDOWN: Interface GigabitEthernet1/0/19, changed state to up *Mar 1 00:15:32.628: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/19, changed state to up *Mar 1 00:15:44.632: STP: VLAN0001 Gi1/0/19 -> learning *Mar 1 00:15:59.639: STP: VLAN0001 Gi1/0/19 -> forwarding Next I ran the same test with portfast enabled interface GigabitEthernet1/0/19 switchport mode access switchport nonegotiate shutdown spanning-tree portfast Switch(config)#int g1/0/19 Switch(config-if)#no shut *Mar 1 00:18:40.567: %LINK-3-UPDOWN: Interface GigabitEthernet1/0/19, changed state to down *Mar 1 00:18:41.053: setting bridge id (which=3) prio 32769 prio cfg 32768 sysid 1 (on) id 8001.0023.ab49.6e00 *Mar 1 00:18:41.061: set portid: VLAN0001 Gi1/0/19: new port id 8013 *Mar 1 00:18:41.061: STP: VLAN0001 Gi1/0/19 ->jump to forwarding from blocking So the port transitioned within one second here and there was no 20 second blocking. All in all these tests show that I didn't spend 20 seconds in blocking regardless of portfast being enabled or not upon port initialization Cheers! Thank you, Steve E. Di Bias | Network Engineer CCNP (R&S), CCNA (R&S/Security), FNCNE, BCNE, CE|H, CCA, MCSE, MCSA, MCTS, MCITP, A+, Net+ Valley Health System | www.valleyhealthsys.com Direct: 702-369-7594 | Mobile: 702-241-1801 Email: [email protected] -----Original Message----- From: [email protected] [mailto: [email protected]] On Behalf Of James Roc Sent: Tuesday, November 29, 2011 10:29 PM To: imad Abdallah Cc: [email protected] Subject: Re: [OSL | CCIE_RS] Vol2 Lab 10 Spanning Tree Timer You are correct Imad, check out: http://onlinestudylist.com/archives/ccie_rs/2011-November/016005.html On Wed, Nov 30, 2011 at 4:33 PM, imad Abdallah <[email protected] >wrote: In the task they said that: "When the links initially come up, they should wait 44 sec to start forwarding" In the DSG they solve it by setting the forward-delay timer to 12 sec: 20 sec (max age timer) + 12 sec (forward delay) + 12 sec (forward delay) = 44 Is this correct?As I know, the max age timer is only used when an indirect link failure has occurred. It'll not be used when the port first comes up or when a direct link failure occurs.So the solution should be to set the forward delay timer to 22 sec!! _______________________________________________ For more information regarding industry leading CCIE Lab training, please visit www.ipexpert.com Are you a CCNP or CCIE and looking for a job? Check out www.PlatinumPlacement.com http://onlinestudylist.com/mailman/listinfo/ccie_rs _______________________________________________ For more information regarding industry leading CCIE Lab training, please visit www.ipexpert.com Are you a CCNP or CCIE and looking for a job? Check out www.PlatinumPlacement.com http://onlinestudylist.com/mailman/listinfo/ccie_rs UHS Confidentiality Notice: This e-mail message, including any attachments, is for the sole use of the intended recipient (s) and may contain confidential and privileged information. Any unauthorized review, use, disclosure or distribution of this information is prohibited. If this was sent to you in error, please notify the sender by reply e-mail and destroy all copies of the original message. _______________________________________________ For more information regarding industry leading CCIE Lab training, please visit www.ipexpert.com Are you a CCNP or CCIE and looking for a job? Check out www.PlatinumPlacement.com http://onlinestudylist.com/mailman/listinfo/ccie_rs _______________________________________________ For more information regarding industry leading CCIE Lab training, please visit www.ipexpert.com Are you a CCNP or CCIE and looking for a job? Check out www.PlatinumPlacement.com http://onlinestudylist.com/mailman/listinfo/ccie_rs
