Refer to the exhibit. The network administrator configures both switches as displayed. However, host C is unable to ping host D and host E is unable to ping host F. What action should the administrator take to enable this communication?

The exhibit shows the configuration of the trunk links between two switches, SW1 and SW2. Both switches have their trunk ports set to “dynamic auto” mode and are using VLAN 666 as the native VLAN. Hosts C and D are on VLAN 10, while Hosts E and F are on VLAN 30. Since Host C is unable to ping Host D and Host E is unable to ping Host F, there appears to be an issue with VLANs communication across the trunk link.

Here are the potential issues and the actions that could resolve the communication problems:

1. Mismatched Trunk Negotiation Modes:
   • With both interfaces set to “dynamic auto,” neither switch is actively attempting to form a trunk, which can result in the link not forming a trunk at all. The solution would be to set at least one side to “dynamic desirable” to actively attempt to form a trunk, which is necessary for the VLANs to communicate across the switches.
2. Native VLAN Mismatch:
   • If there is a native VLAN mismatch and VLAN 666 is not used on both ends of the trunk or by the hosts, it could cause traffic from the native VLAN to be untagged and not understood on the opposite switch. However, the configuration shows the same native VLAN, so this is not likely the issue.
3. VLANs not allowed on the trunk:
   • The configurations provided do not show the ‘switchport trunk allowed vlan’ command. If VLANs 10 and 30 are not explicitly allowed on the trunk, this would prevent traffic from those VLANs from crossing the trunk. The administrator should ensure that all necessary VLANs are allowed on the trunk.
4. No switchport nonegotiate:
   • The ‘switchport nonegotiate’ command prevents DTP (Dynamic Trunking Protocol) frames from being sent out of the port. However, if both sides are set to dynamic auto and the link is not establishing as a trunk, it’s not a negotiation issue. This command would be more relevant if one end of the trunk were set to a non-negotiable mode, like static access or trunk, and you wanted to prevent DTP frames from being sent.

Based on the output and the possible issues, the action that the administrator should take to enable communication between Host C and Host D as well as Host E and Host F is likely:

Configure either trunk port in the dynamic desirable mode.

This will actively attempt to form a trunk. It is important to note that “dynamic auto” mode will not form a trunk unless the other end is in “dynamic desirable” or “trunk” mode. Setting one end to “dynamic desirable” will initiate trunking and allow traffic from VLANs 10 and 30 to pass through.