| In your BCMSN / CCNP exam study, it's easy to | | | | |
| overlook some of the details of Spanning Tree | | | | SW1(config)#spanning-tree vlan 1 hello-time 5 |
| Protocol (STP). After all, you learned all of | | | | |
| that in your CCNA studies, right? Not | | | | SW1(config)#spanning-tree vlan 1 max-age 30 |
| necessarily! While some of the BCMSN material | | | | |
| will be a review for you, there are some | | | | SW1(config)#spanning-tree vlan 1 forward-time |
| details regarding familiar topics that you | | | | 20 |
| need to learn. That includes the timers for | | | | |
| STP - Hello Time, MaxAge, and Forward Delay. | | | | SW1(config)#^Z SW1#show spanning-tree |
| | | | vlan 1 |
| You may remember these timers from your CCNA | | | | |
| studies as well, and you should also remember | | | | VLAN0001 |
| that these timers should not be changed | | | | |
| lightly. What you might not have known is | | | | Spanning tree enabled protocol ieee |
| that if you decide to change any and all of | | | | |
| these timers, that change must be configured | | | | Root ID Priority 32769 |
| on the root bridge! The root bridge will | | | | |
| inform the nonroot switches of the change via | | | | Address 000f.90e1.c240 |
| BPDUs. | | | | |
| | | | This bridge is the root |
| Hello Time is the interval between BPDUs, two | | | | |
| seconds by default. | | | | Hello Time 5 sec Max Age 30 sec Forward Delay |
| | | | 20 sec |
| Forward Delay is the length of both the | | | | |
| listening and learning STP stages, with a | | | | Bridge ID Priority 32769 (priority 32768 |
| default value of 15 seconds. | | | | sys-id-ext 1) |
| | | | |
| Maximum Age, referred to by the switch as | | | | Address 000f.90e1.c240 |
| MaxAge, is the amount of time a switch will | | | | |
| retain a BPDU's contents before discarding | | | | Hello Time 5 sec Max Age 30 sec Forward Delay |
| it. The default is 20 seconds. | | | | 20 sec |
| | | | |
| The value of these timers can be changed with | | | | Aging Time 300 |
| the spanning-tree vlan command shown below. | | | | |
| Verify the changes with the show | | | | Interface Role Sts Cost Prio.Nbr Type |
| spanning-tree command. | | | | |
| | | | Fa0/11 Desg FWD 19 128.11 P2p |
| SW1(config)#spanning-tree vlan 1 | | | | |
| ?forward-time Set the forward delay for the | | | | Fa0/12 Desg FWD 19 128.12 P2p |
| spanning treehello-time Set the hello | | | | |
| interval for the spanning treemax-age Set the | | | | Again, you should always take great care in |
| max age interval for the spanning | | | | changing these timers. Those defaults are set |
| treepriority Set the bridge priority for the | | | | for a reason - helping to prevent switching |
| spanning treeroot Configure switch as root | | | | loops! |