A network administrator is investigating a report that newly provisioned database servers residing on VLAN 30 attached to Switch-A cannot communicate with application servers on VLAN 30 connected to Switch-B. Both switches are connected via an 802.1Q trunk on interface GigabitEthernet0/1. The administrator executes a troubleshooting command on Switch-A and observes the following output:
| Port | Mode | Encapsulation | Status | Native vlan |
|---|---|---|---|---|
| Gi0/1 | on | 802.1q | trunking | 1 |
| Port | Vlans allowed on trunk |
|---|---|
| Gi0/1 | 1-20, 40-100 |
Local pings from the database servers to Switch-A's Layer 3 VLAN 30 interface succeed, but traffic crossing to Switch-B is completely dropped. Which of the following identifies the root cause of this connectivity failure?
- VLAN 30 is missing from the list of allowed VLANs configured on the trunk interface.Cevap
- BA native VLAN mismatch exists because Switch-A uses VLAN 1 while Switch-B is configured to send tagged frames for VLAN 30.
- CA duplex mismatch on interface Gi0/1 is causing late collisions that drop all frames tagged with VLAN 30.
- DSwitch-A has been configured with an improper Spanning Tree Protocol (STP) priority, placing interface Gi0/1 into a blocking state.
Cevap
VLAN 30 is missing from the list of allowed VLANs configured on the trunk interface.
The trunk output clearly shows that interface Gi0/1 only permits VLANs in the ranges 1-20 and 40-100. Because VLAN 30 is omitted from this allowed list, Switch-A drops all ingress and egress frames tagged for VLAN 30 on this trunk interface.
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Anahtar Kavram
802.1Q Trunk Allowed VLAN List Pruning