flexible nic and centos appliance

We have a third party centos 6.6  appliance running on ESXi 6.U2 cluster and we are  having  ICMP issue with that appliance.  Ping drops from time to time when we ping that appliance.
I noticed the nic card is flexible. The appliance does not have vmtools so i will not be able to add vmxnet3 .  Is it ok to use flexible nic ? I thought it has to be vlance or E1000 not the flexible.
How do i change this to vlance?
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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
Do NOT change the APPLIANCE without contacting and discussing with the vendor!

Appliances are supplied "as is" with no serviceable parts, e.g. do not change!
sara2000Author Commented:
I have another issue with nic card when i try to vMotion: Warning message as below.
Virtual ethernet card 'Network adapter 1' is not supported. "This is not a limitation of the host in general, but of the virtual machine's configured guest OS on the selected host."
Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
Discuss with vendor of appliance.

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