Successful inter-VLAN routing has been operating on a network with multiple VLANs across multiple switches for some time. When an inter-switch trunk link fails and Spanning Tree Protocol brings up a backup trunk link, it is reported that hosts on two VLANs can access some, but not all the network resources that could be accessed previously. Hosts on all other VLANS do not have this problem. What is the most likely cause of this problem?
- The allowed VLANs on the backup link were not configured correctly.
- The protected edge port function on the backup trunk interfaces has been disabled.
- Dynamic Trunking Protocol on the link has failed.
- Inter-VLAN routing also failed when the trunk link failed.
Answers Explanation & Hints:
The most likely cause of the problem is that the allowed VLANs on the backup link were not configured correctly. When an inter-switch trunk link fails and a backup trunk link is brought up by Spanning Tree Protocol, the VLAN information must be properly configured on the backup link in order for the VLANs to function as they did previously. If the allowed VLANs on the backup link are not configured correctly, some resources may not be accessible to hosts on certain VLANs. This can explain why hosts on two VLANs are having problems while hosts on all other VLANs do not.