In an enterprise network operating Rapid PVST+ for VLAN 20, three Catalyst switches are in… — Cisco CCNA

In an enterprise network operating Rapid PVST+ for VLAN $20$ , three Catalyst switches are interconnected as follows:

- Switch-A is configured with a base bridge priority of $4096$ and MAC address `0011.1111.1111`.
- Switch-B is configured with a base bridge priority of $28672$ and MAC address `0022.2222.2222`.
- Switch-C is configured with a base bridge priority of $28672$ and MAC address `0033.3333.3333`.

Switch-B and Switch-C both connect directly to Switch-A using single $1\text{ Gbps}$ trunk links on interface GigabitEthernet 0/1. In addition, Switch-B and Switch-C are connected directly to each other via two parallel $1\text{ Gbps}$ trunk links: Link 1 connects interface GigabitEthernet 0/2 on both switches, and Link 2 connects interface GigabitEthernet 0/3 on both switches. All switches maintain default port priorities of $128$ .

Based on Rapid PVST+ operations for VLAN $20$ , what are the port role and operational state of interface GigabitEthernet 0/3 on Switch-C?

Alternate role and Discarding stateCevap
B
Backup role and Discarding state
C
Designated role and Forwarding state
D
Alternate role and Blocking state

Cevap

Interface GigabitEthernet 0/3 on Switch-C operates in the Alternate role and Discarding state.

In Rapid PVST+, Switch-A is elected Root Bridge because it has the lowest Bridge ID (

4116

). Switch-B and Switch-C both select GigabitEthernet 0/1 as their Root Port with a path cost of

4

. On the parallel links between Switch-B and Switch-C, Switch-B wins the Designated Port election for both segments because its MAC address (`0022.2222.2222`) is lower than Switch-C's MAC address (`0033.3333.3333`), breaking the path cost tie. Because Switch-C receives BPDUs from a neighboring switch on GigabitEthernet 0/2 and 0/3, both interfaces serve as redundant paths to the root and are assigned the Alternate port role. Rapid PVST+ replaces the legacy 802.1D Blocking state with the Discarding state for non-forwarding ports.

Adım Adım Çözüm

Determine the Root Bridge for VLAN 20.

Switch-A Bridge Priority (

4096 + 20 = 4116

) is lower than Switch-B and Switch-C (

28672 + 20 = 28692

). Switch-A is elected Root Bridge.

The bridge with the lowest Bridge ID (Priority + System ID Extension + MAC) becomes the Root Bridge.

Determine Root Ports on non-root switches.

Switch-B GigabitEthernet 0/1 (Cost

4

) and Switch-C GigabitEthernet 0/1 (Cost

4

) are elected Root Ports.

Direct

1\text{ Gbps}

links to Switch-A provide the lowest cumulative Root Path Cost (

4

Evaluate Designated Port selection between Switch-B and Switch-C on parallel links (Gi0/2 and Gi0/3).

Switch-B advertises Root Path Cost

4

, Switch-C advertises Root Path Cost

4

. Ties are broken by Sender Bridge ID. Switch-B MAC (`0022.2222.2222`) < Switch-C MAC (`0033.3333.3333`). Switch-B wins Designated role on both Gi0/2 and Gi0/3.

On a segment between two switches with equal Root Path Cost, the switch with the lower Bridge ID becomes the Designated Switch.

Determine the port role and state for Switch-C's interfaces GigabitEthernet 0/2 and 0/3.

Both Gi0/2 and Gi0/3 on Switch-C receive superior BPDUs from Switch-B (a foreign switch). They are assigned the Alternate role and placed in the Discarding state.

In Rapid PVST+ (802.1w), ports receiving BPDUs from another switch that offer an alternate path to the root are Alternate ports and reside in the Discarding state.

Anahtar Kavram

Rapid PVST+ Port Roles (Root, Designated, Alternate, Backup) and 802.1w Operational States (Discarding, Learning, Forwarding)

Tahmini Süre:2m 0s

Soru

Cevap

Adım Adım Çözüm

Anahtar Kavram

Sık Yapılan Hatalar

Konular

Bu konudan daha fazla soru