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