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Zorluk: OrtaSpanning Tree Protocol Operations

Four switches—Switch-A, Switch-B, Switch-C, and Switch-D—are interconnected in a square physical ring topology using 1 Gbps Ethernet links (default STP path cost of 4). The switches are configured with standard IEEE 802.1D Spanning Tree Protocol using the following Bridge IDs:

- Switch-A: Priority 32768, MAC Address 00:11:22:33:44:AA
- Switch-B: Priority 32768, MAC Address 00:11:22:33:44:BB
- Switch-C: Priority 4096, MAC Address 00:11:22:33:44:CC
- Switch-D: Priority 32768, MAC Address 00:11:22:33:44:DD

Which TWO of the following statements regarding the resulting Spanning Tree Protocol (STP) topology and port roles are correct?

  1. Switch-C is elected as the Root Bridge because it has the lowest numerical Bridge Priority value.Cevap
  2. Switch-B transitions its interface connected to Switch-D into the Blocking state to eliminate the Layer 2 loop.Cevap
  3. C
    Switch-A is elected as the Root Bridge because its MAC address is numerically lower than Switch-B, Switch-C, and Switch-D.
  4. D
    Switch-B selects its interface connected to Switch-D as its Root Port because Switch-D presents a higher MAC address.
  5. E
    A native VLAN mismatch across the trunk link between Switch-B and Switch-C will force all switches to immediately reset their STP port states to Forwarding.

Cevap

The correct statements indicate that Switch-C becomes the Root Bridge due to having the lowest bridge priority (4096), and Switch-B places its interface connected to Switch-D into the Blocking state due to higher root path cost on that segment compared to Switch-D.
The election of the Root Bridge prioritizes the lowest Bridge Priority (4096 on Switch-C vs 32768 on others). On the segment between Switch-B and Switch-D, Switch-D advertises a lower Root Path Cost (4) to the Root Bridge than Switch-B (8), making Switch-D's port Designated and causing Switch-B to block its port to prevent loops.

Adım Adım Çözüm

1
Determine the Root Bridge election outcome.
Compare Bridge IDs (Priority + MAC). Switch-C has priority 4096; all others have priority 32768. Switch-C is elected as Root Bridge.
STP selects the switch with the lowest numerical Bridge ID, evaluating priority first.
2
Calculate Root Path Costs for non-root switches.
Switch-A (cost 4 direct to Switch-C), Switch-D (cost 4 direct to Switch-C), Switch-B (cost 8 via Switch-A or Switch-D).
Each 1 Gbps link adds a path cost of 4 to the cumulative distance to the Root Bridge.
3
Determine Root Ports for non-root switches.
Switch-A and Switch-D set their direct links to Switch-C as Root Ports. Switch-B compares upstream neighbors Switch-A (MAC 44:AA) and Switch-D (MAC 44:DD). Switch-B selects the port facing Switch-A as its Root Port.
When path costs are equal, the lower designated bridge ID is preferred.
4
Determine Designated and Alternate/Blocking Ports on the segment between Switch-B and Switch-D.
Switch-D has a lower root path cost (4) than Switch-B (8). Switch-D's port becomes Designated, while Switch-B's port becomes Alternate/Blocking.
On shared links, the switch advertising the lower root path cost owns the Designated Port; the other side blocks.

Anahtar Kavram

STP Root Bridge Election and Port Role Determination
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Konular

Spanning Tree Protocol Operations

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