STP-Full
Root Bridge Election Process:
++Hello BPDU
Each BPDU carries
1.Root Bridge ID
2.Cost to the Root Bridge(cost between this switch and the current root)
++Hello BPDU
Each BPDU carries
1.Root Bridge ID
2.Cost to the Root Bridge(cost between this switch and the current root)
#show spanning-tree VLAN 10:-
NOTE:-BY default Cisco IOS runs PVST+. That means your switch will run the STP instance for each VLANs
Bridge Identifier= (Bridge Priority + MAC address) MAC add=mac address of the switch you are on.
Bridge Priority=(switch Priority+ Extended system Id) (32768+10) ==32778 lowest priority is Preferred as ROOT
switch priority= it should be increments of 4096
% Allowed values are:
0 4096 8192 12288 16384 20480 24576 28672
32768 36864 40960 45056 49152 53248 57344 61440
0 4096 8192 12288 16384 20480 24576 28672
32768 36864 40960 45056 49152 53248 57344 61440
ROOT Identifier=same as above (Bridge Priority + MAC address) MAC add=mac address of the ROOT Switch.
If the bridge ID and root ID are the same then you are on the root bridge for that vlan.
SW2#spanning-tree vlan 10 Priority 4096
SW1(BP=32768)------SW2(BP=4096)
SW2=ROOT
STP TIMERS:-
Hello time:-2sec, sends hello every 2sec
MAX age:-10*(hellotime)=20sec
Forward delay Time:- (15sec)(listening=15,lerning=15)
MAX age:-10*(hellotime)=20sec
Forward delay Time:- (15sec)(listening=15,lerning=15)
If a LINK/PORT IS DOWN or if it receiving a NEW BPDU packets then ELECTION HAPPEN like below.
STP Logs without Backbone fast:-
*Mar 1 02:24:30.557: STP: VLAN0001 heard root 32769-0012.0100.4d00 on Gi1/0/1
*Mar 1 02:24:32.402: STP: VLAN0001 heard root 32769-0012.0100.4d00 on Gi1/0/1
*Mar 1 02:24:34.407: STP: VLAN0001 heard root 32769-0012.0100.4d00 on Gi1/0/1
*Mar 1 02:24:36.412: STP: VLAN0001 heard root 32769-0012.0100.4d00 on Gi1/0/1
*Mar 1 02:24:38.417: STP: VLAN0001 heard root 32769-0012.0100.4d00 on Gi1/0/1
*Mar 1 02:24:40.422: STP: VLAN0001 heard root 32769-0012.0100.4d00 on Gi1/0/1
*Mar 1 02:24:42.427: STP: VLAN0001 heard root 32769-0012.0100.4d00 on Gi1/0/1
*Mar 1 02:24:44.440: STP: VLAN0001 heard root 32769-0012.0100.4d00 on Gi1/0/1
*Mar 1 02:24:46.436: STP: VLAN0001 heard root 32769-0012.0100.4d00 on Gi1/0/1
*Mar 1 02:24:48.441: STP: VLAN0001 heard root 32769-0012.0100.4d00 on Gi1/0/1
*Mar 1 02:24:48.550: STP: VLAN0001 Gi1/0/1 -> listening
*Mar 1 02:24:49.599: STP: VLAN0001 Topology Change rcvd on Gi1/0/1
*Mar 1 02:24:49.599: STP: VLAN0001 sent Topology Change Notice on Gi1/0/2
*Mar 1 02:25:03.558: STP: VLAN0001 Gi1/0/1 -> learning
*Mar 1 02:25:18.565: STP: VLAN0001 sent Topology Change Notice on Gi1/0/2
*Mar 1 02:25:18.565: STP: VLAN0001 Gi1/0/1 –> forwarding
*Mar 1 02:24:30.557: STP: VLAN0001 heard root 32769-0012.0100.4d00 on Gi1/0/1
*Mar 1 02:24:32.402: STP: VLAN0001 heard root 32769-0012.0100.4d00 on Gi1/0/1
*Mar 1 02:24:34.407: STP: VLAN0001 heard root 32769-0012.0100.4d00 on Gi1/0/1
*Mar 1 02:24:36.412: STP: VLAN0001 heard root 32769-0012.0100.4d00 on Gi1/0/1
*Mar 1 02:24:38.417: STP: VLAN0001 heard root 32769-0012.0100.4d00 on Gi1/0/1
*Mar 1 02:24:40.422: STP: VLAN0001 heard root 32769-0012.0100.4d00 on Gi1/0/1
*Mar 1 02:24:42.427: STP: VLAN0001 heard root 32769-0012.0100.4d00 on Gi1/0/1
*Mar 1 02:24:44.440: STP: VLAN0001 heard root 32769-0012.0100.4d00 on Gi1/0/1
*Mar 1 02:24:46.436: STP: VLAN0001 heard root 32769-0012.0100.4d00 on Gi1/0/1
*Mar 1 02:24:48.441: STP: VLAN0001 heard root 32769-0012.0100.4d00 on Gi1/0/1
*Mar 1 02:24:48.550: STP: VLAN0001 Gi1/0/1 -> listening
*Mar 1 02:24:49.599: STP: VLAN0001 Topology Change rcvd on Gi1/0/1
*Mar 1 02:24:49.599: STP: VLAN0001 sent Topology Change Notice on Gi1/0/2
*Mar 1 02:25:03.558: STP: VLAN0001 Gi1/0/1 -> learning
*Mar 1 02:25:18.565: STP: VLAN0001 sent Topology Change Notice on Gi1/0/2
*Mar 1 02:25:18.565: STP: VLAN0001 Gi1/0/1 –> forwarding
TOTAL TIME=20+15+15=50SEC
MAX AGE(20)+FORWARD DELAY(30)
STP Logs with Backbone fast:- In backbonefast it bypasses Maxage(20sec) Time.
*Mar 1 03:20:32.795: STP: VLAN0001 heard root 32769-000d.2818.af00 on Fa1/0/2
*Mar 1 03:20:32.795: STP: VLAN0001 Fa1/0/2 -> listening
*Mar 1 03:20:33.801: STP: VLAN0001 Topology Change rcvd on Fa1/0/2
*Mar 1 03:20:33.801: STP: VLAN0001 sent Topology Change Notice on Fa1/0/40
*Mar 1 03:20:47.802: STP: VLAN0001 Fa1/0/2 -> learning
*Mar 1 03:21:02.809: STP: VLAN0001 sent Topology Change Notice on Fa1/0/40
*Mar 1 03:21:02.809: STP: VLAN0001 Fa1/0/2 -> forwarding
*Mar 1 03:20:32.795: STP: VLAN0001 Fa1/0/2 -> listening
*Mar 1 03:20:33.801: STP: VLAN0001 Topology Change rcvd on Fa1/0/2
*Mar 1 03:20:33.801: STP: VLAN0001 sent Topology Change Notice on Fa1/0/40
*Mar 1 03:20:47.802: STP: VLAN0001 Fa1/0/2 -> learning
*Mar 1 03:21:02.809: STP: VLAN0001 sent Topology Change Notice on Fa1/0/40
*Mar 1 03:21:02.809: STP: VLAN0001 Fa1/0/2 -> forwarding
TOTAL TIME=0+15+15=30SEC
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