CCNA Notes
—- CompTIA LX103
Cisco ICND1
Cisco ICND2
- Topics
- To
- Be
- Added
Various
Labs
—- CompTIA LX103
Cisco ICND1
Cisco ICND2
Various
Labs
This is an old revision of the document!
Frame Loop Prevention Mechanism. Achieved by blocking all but one ROOT port to a ROOT switch. Redundant links are then blocked to create a loop-free environment.
Note that once a ROOT Bridge is elected, all other bridges will only forward HELLO BPDU's originating from the ROOT BRIDGE. The Root cost is incremented as the HELLO BPDU is received (COST=$COST+$PORT_COST). The Root Cost starts off @ 0 from the ROOT. Each subsequent Bridge tacks on it's COST TO THE ROOT BRIDGE as it is received.
SW1(config)#spanning-tree vlan 1 root primary SW1(config)#spanning-tree vlan 1 root secondary
SW2(config)#spanning-tree vlan 1 priority ? <0-61440> bridge priority in increments of 4096 SW2(config)#spanning-tree vlan 1 priority 4096 Hello Max Fwd Vlan Bridge ID Time Age Dly Protocol ---------------- --------------------------------- ----- --- --- -------- VLAN0001 4097(4096, 1) 0019.e86a.2280 2 20 15 ieee <-- LOWER PRIORITY = ROOT BRIDGE! VLAN0002 32770(32768, 2) 0019.e86a.2280 2 20 15 ieee
SW2(config)#int fa0/1 SW2(config-if)#spanning-tree vlan 2 cost 1 SW2(config-if)# SW2(config-if)#do sh spann int fa0/1 Vlan Role Sts Cost Prio.Nbr Type ------------------- ---- --- --------- -------- -------------------------------- VLAN0001 Desg FWD 19 128.1 P2p VLAN0002 Root FWD 1 128.1 P2p <-- NOTICE THE COST! LOWER COST = ROOT PORT!