How state mac table in physical switch when virtual machine connect to it?

Hamid Saeed
Hamid Saeed used Ask the Experts™
Hi dears,
Can you help  me for :
 In scenario below:
In a esxi host with a uplink that connet to a upstream  switch, exist 5 VMs that  each have thier broad cast domain ,
My question is,  
When VMs start for connect to external network, I want know  what mac table switch is?
I want know a switch port how understand many VMs connected to it?

Very thanks for your helps,
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Excuse me friends,
Do my question  is vague?
kevinhsiehNetwork Engineer

If there are multiple VMs on a host, the physical switch will see multiple MAC addresses on that switch port, just like it would if you plugged in another physical switch and had multiple devices connected. It isn't any different because of virtualization.


Thanks dear,
Excuse me, let to me explain more,
I want know with a uplink and many VMs with different subnets, that uplink connect to one physical  switch , I want know how traffics from VMs send out to external network and how switch behavior with VMs traffics ?

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This is done using VLAN trunking or 802.1Q.

This protocol adds a header to each ethernet packet that allows both switch and VM host to identify to which subnet the traffic should be directed.

So you can have different subnets on one physical cable, being logically separated by the 802.1Q protocol. Within each subnet, things work like they usually do.


Very thanks friends,
Ok, if I have three port groups that with thier subnets, I don't want use vlan Id for them,
Now physical  switch how see this traffics and how vsphere send vm's traffic  to physical switch and how switch pass traffic of VMs from external network to each of VMs?

Very thanks for your helps,
I'm not sure what you're asking or what you're trying to accomplish?

By definition 802.1Q uses VLANs and traffic is separated by this protocol as if each VLAN had it's own physical infrastructure. So you can't say that you don't want to use VLANs because this works entirely based upon VLANs.

If you want to know how this works in detail, just google for it. It's not practical for me to try to explain 802.1Q in a few lines as this requires diagrams etc. and there are many fine websites that do a good job at explaining it.


Thanks dear for your answers,

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