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I am using VMWare ESXi 5.
The ESXi 5 host has a NIC with the MAC XXXX:XXXX:XXXX
I have created a console port for that card.
I have added a new guest named COMP and manually assigned the MAC address of the physical NIC (XXXX:XXXX:XXXX - same as the NIC of the ESXi server).
Now COMP reports it has a NIC with IP Y.Y.Y.Y, same IP in VMWare port definition.

COMP will not respond to pings.

When I logged in to the ESXi host via SSH and tried to ping other computers connected to it, COMP responded to pings for the rest of the day. After a pingless night (or no communication to COMP) - COMP returned to the point of not responding to pings again.

  1. What's happening there?
  2. IS there a way to resolve this issue such that COMP will always respond to pings?

Here are the full details: I am trying to test driver setup of a NIC I personally develop.

Up until now I had to install a new machine for the test. Lately I encountered VMware, and I thought it can be set up to virtualize a machine such that it's NIC behaves just like the physical NIC of the virtual machine.

This question led me to believe this setup was possible: Can't ping host from vmware guest using bridged networking.

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Why does this guest have to share the same MAC address as the host, and have you tried it with a different address? To be honest, I'm having trouble parsing your question, but I can't see having a guest with the same MAC address as the host being a particularly good thing. It's almost certain to cause some weird issue, whether this is one of them or not. – Dan Nov 15 '12 at 13:54
Bridged networking does NOT require the guest to have the same MAC as the host. In fact, tht breaks a lot of stuff. – MDMarra Nov 16 '12 at 12:53
If you have a link to a VMWare knowledge base article or other documentation on what you're describing I'd love to read it. – MDMarra Nov 16 '12 at 13:11
Please, just trust us on this one. You're doing something wrong. Stop. – pauska Nov 16 '12 at 13:40
What happens if you set the MAC to one different from the physical host? Also, from Wikipedia: A Media Access Control address (MAC address) is a unique identifier assigned to network interfaces for communications on the physical network segment. Unique. One-of-a-kind. I assure you, no machine on the same network should have the same Mac. VirtualBox's bridged network mode does not need this. – tombull89 Nov 16 '12 at 13:54
  1. A MAC address conflict is what's happening. Since you have two objects with the same MAC address, packets bound for either device will end up at one or the other, and where you "intend" for them to go doesn't matter a whole lot.

  2. Don't assign the same MAC address to your "COMP" as you have for your VMWare server. MAC addresses should be unique, when you have duplicates on your network things like this happen.

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1. This is not true. VMWARE allows you to setup same MAC address to multiple virtualized computers, and it will foreward the address to all. Pings should be seen on bott VMWARE server, and virtualized computer. 2. then how do I bridge the two cards such that I can see what happens on the physical NIC using a vitual machine? – Henry Aloni Nov 16 '12 at 12:26
@Henry your assertion is really just incorrect. If you want to see what's happening on the host NIC from a guest, you need Enterprise Plus licenses so that you can use the Nexus V1000 vSwitch, which allows you to configure port mirrors. – MDMarra Nov 16 '12 at 13:00
@HenryAloni 1. Yes, VMWare will let you do this. Doesn't mean it's a good idea. VMWare will also let you delete the virtual disk files for your VMs, but that doesn't mean you should do that and expect the VMs to work. 2. What are you actually trying to do? Meaning - why not monitor the physical machine's NIC, from the physical machine? – HopelessN00b Nov 16 '12 at 14:29
About 2: I want to monitor the card on physical machine, but I don't want to buy a new HD/computer/else for every setup (OS) I want to check. This thing is what virtualized environments are best at. – Henry Aloni Nov 17 '12 at 12:00
@HenryAloni This is the Wrong way to do this. The Right way is a mirror port on your switch and a network card (physical or virtual) in Promiscuous Mode eating all the traffic. Duplicate MAC addresses are an abomination in violation of the ethernet specification, and this is not one of the extremely rare cases I can think of where you'd want that kind of thing... – voretaq7 Nov 17 '12 at 21:53

To address your most recent content update, if you want to "pass" the physical NIC through to the guest. This article describes it for ESXi 4 and this article walks you through it for ESXi 5. You use DirectPath I/O to present the physical NIC directly to the guest. When you do this, the host will not use that NIC at all.

The way you're trying to do it now is just basically causing you to arp poison yourself.

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This is partially correct. After doing the steps in ESXi 5 you get a message saying that if the card does not behave as expected - you should add a static MAC address same as physical NIC you are connecting the VM to. Also - it seems that there's no ARP poisoning after doing this step. After the second ARP request it seems that the VM is in charge of the card. – Henry Aloni Nov 16 '12 at 19:21
No, it's fully correct. – Basil Nov 19 '12 at 14:02

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