Cisco Catalyst 3750 switch port for VMWare ESX

Question

We have a VMWare ESXi host with a single network port. It's connected to a Cisco Catalyst 3750 switch port and the configuration of thew switch port is as follows:

interface FastEthernet 1/0/2
 switchport access vlan 10
 switchport mode access
end

We need to run a guest on a separate vlan (vlan 11 and 12) and so we change the switch configuration as follows:

interface FastEthernet 1/0/2
 switchport trunk encapsulation dot1q 
 switchport mode trunk
 switchport trunk native vlan 10
 switchport trunk allowed vlan add 10,11,12
end

When this is done we lose access to the host. What is wrong with this configuration?

Answer 1

ESXi does not support DTP dynamic trunking protocol and portfast trunk should be enabled.

switchport nonegotiate !Skip DTP negotiation
spanning-tree portfast trunk !Fast forward STP state

In addition, do not use the native (untagged) vlan on any portgroups. Use the native vlan for the management or service-console VMKernel networks which also allow kickstarting for installs over DHCP or BOOTP before tagging can be used.