2. Consider this switched network (from CNA Scaling Networks 2.1.2.8). Please ig

Question

2. Consider this switched network (from CNA Scaling Networks 2.1.2.8). Please ignore the boxes drawn on top of each inter-switch link. Assume that Spanning Tree Protocol (STP) is running on this network. The table below shows the Bridge ID (BID) value for each switch, split into Priority and MAC Address parts. All ports are on VLAN 1 G1/1 S1 S2 Fa0/1 G1 G1/3 G1/1 Fa0/1 S3 S4 Priority 32769 24577 32769 32769 MAC Address S1 S2 S3 S4 000A00222222 000A00333333 000A00444444 (5 points) When STP protocol is run, which switch (S1, S2, S3 or S4) will become the Root Switch for this network? Why? a.

Explanation / Answer

a.

The Bridge ID is composed of the bridge priority value and the bridge MAC address.
Bridge ID = Bridge Priority + MAC Address
The Switch with lowest Bridge ID is selected as Root Port.

To compare two bridge IDs, the priority is compared first.
If two bridges have equal priority, then the MAC addresses are compared.
In the table, S1, S3, and S4 have the same Priority value.
But S2 has the lowest priority value so it will become the root bridge.

So S2 is selected as Root Port

b.

i. S1 Fa0/1 : Designated Port
ii. S1 G1/1 : Root port
iii. S2 G1/1 : Designated Port
iv. S2 G1/2 : Designated Port
v. S2 G1/3 : Designated Port
vi. S3 Fa0/1 : Alternate Port
vii. S3 G1/1 : Root port
viii.S4 G1/1 : Root port
  
c.

The S3 Fa0/1 port will go into Blocking state.

e.

Switch(config-if)# spanning-tree port-priority 0

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