An enterprise network uses Rapid PVST+ across four switches (SW1, SW2, SW3, SW4) configure… — Cisco CCNA

An enterprise network uses Rapid PVST+ across four switches (SW1, SW2, SW3, SW4) configured for VLAN 50. All switches operate with default STP settings except for the bridge priority values specified below:

- SW1: Bridge Priority = $24576$ , MAC = $0001.0000.0011$
- SW2: Bridge Priority = $32768$ , MAC = $0001.0000.0022$
- SW3: Bridge Priority = $32768$ , MAC = $0001.0000.0033$
- SW4: Bridge Priority = $32768$ , MAC = $0001.0000.0044$

The physical interconnections and short path costs for VLAN 50 are as follows:
- SW1 connects to SW2 via Gi1/0/1 ( $1\text{ Gbps}$ link, STP cost = $4$ ) and to SW3 via Gi1/0/2 ( $10\text{ Gbps}$ link, STP cost = $2$ ).
- SW2 connects to SW3 via Gi1/0/2 ( $10\text{ Gbps}$ link, STP cost = $2$ ).
- SW4 connects to SW2 via Gi1/0/1 ( $1\text{ Gbps}$ link, STP cost = $4$ ) and to SW3 via Gi1/0/2 ( $1\text{ Gbps}$ link, STP cost = $4$ ).

After Rapid PVST+ converges, what are the port role and port state of interface Gi1/0/1 on SW4 for VLAN 50?

Alternate port in the Discarding stateCevap
B
Root port in the Forwarding state
C
Designated port in the Forwarding state
D
Backup port in the Discarding state

Cevap

Alternate port in the Discarding state

SW1 is elected Root Bridge because it has the lowest Bridge Priority (

24576

). SW3's Root Path Cost to SW1 is

2

(via its direct

10\text{ Gbps}

link), while SW2's Root Path Cost to SW1 is

4

(via its direct

1\text{ Gbps}

link). When evaluating SW4, its path through SW3 yields a total cost of

6

(

4 + 2

), whereas its path through SW2 yields a total cost of

8

(

4 + 4

). SW4 chooses Gi1/0/2 as its Root Port in the Forwarding state. For the segment between SW2 and SW4, SW2 advertises a lower Root Path Cost (

4

) than SW4 (

6

), making SW2 the Designated Bridge. Consequently, SW4's interface Gi1/0/1 is non-designated and operates as an Alternate port in the Discarding state.

Adım Adım Çözüm

Determine the Root Bridge for VLAN 50.

SW1 has the lowest Bridge Priority (

24576

) and is elected as the Root Bridge.

Bridge ID comparison evaluates Bridge Priority + System ID Extension first, then MAC address.

Calculate the Root Path Cost for SW2, SW3, and SW4 to SW1.

SW3 Root Path Cost =

2

(via Gi1/0/2 direct

10\text{ Gbps}

link). SW2 Root Path Cost =

4

(via Gi1/0/1 direct

1\text{ Gbps}

link).

SW3 uses its direct

10\text{ Gbps}

link (cost 2). SW2 uses its direct

1\text{ Gbps}

link (cost 4).

Evaluate SW4's root path options to select SW4's Root Port.

Path via SW3: SW4 Gi1/0/2 cost (

4

) + SW3 Root Path Cost (

2

) =

6

. Path via SW2: SW4 Gi1/0/1 cost (

4

) + SW2 Root Path Cost (

4

) =

8

. SW4 selects Gi1/0/2 as its Root Port.

Rapid PVST+ selects the port leading to the lowest cumulative Root Path Cost.

Determine the Designated Bridge and port roles on the SW2-SW4 link (SW4 Gi1/0/1).

SW2 advertises Root Path Cost =

4

, while SW4 advertises Root Path Cost =

6

. SW2 wins Designated Bridge status on the segment. SW4 Gi1/0/1 becomes an Alternate port in the Discarding state.

The switch with the lower advertised Root Path Cost becomes the Designated Bridge on a shared segment. The non-designated port on the non-root switch receives BPDUs and transitions to the Alternate role in the Discarding state.

Anahtar Kavram

Rapid PVST+ Root Port Election and Alternate Port Role Determination

Soru

Cevap

Adım Adım Çözüm

Anahtar Kavram

Sık Yapılan Hatalar

Konular

Bu konudan daha fazla soru