How does a vm choose a NIC to use

With 6-8 NICs in a host. how does a windows guest choose a NIC to use? - NIC teaming has all tick boxes unticed except notify switches. - What is to stop say 4or 5 VMs from all using the same vmnic and hence the same physical NIC and switch port?
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philb19Asked:
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dipopoCommented:
I must say the question is counter intuitive [No bad meant].

Because the solution above is not using NIC teaming hence would not be load balanced over multiple NIC's but rather over the single NIC assigned to the vSwitch, that is if you have 1 NIC per vSwitch.

If you have multiple vmnics per vSwitch then what are their status ? All active, standby or un-used?.

I think you are referencing the load-balancing options which calculates a vmnic to assign a VM to as observed by just only:

Port ID and MAC hash LB

IP hash performs differently.


To identify which vmnic is actively used by a VM use ESXTOP from the ESXCLI console and type n.
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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
You assign a virtual machine portgroup, which is connected to a vSwtich, and the vSwitch is connected to physical network uplinks (network interface cards).

If you want to read more on networking in VMware ESX/ESXi, then I recommend the following:-

I would also recommend reading through the Networking Sections of the following guides to gain a better understanding of Networking in VMware ESX/ESXi.

Pages 13 - 73 Discuss Networking in Detail, including trunks, VLANs, switches, and load balancing

ESXi Configuration Guide ESXi 4.1

http://www.vmware.com/pdf/vsphere4/r41/vsp_41_esxi_server_config.pdf

Virtual Networking

http://www.vmware.com/technical-resources/virtual-networking/virtual-networks.html

Virtual Networking Concepts

http://www.vmware.com/files/pdf/virtual_networking_concepts.pdf
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philb19Author Commented:
hi all thanks

I have 6 vmNICS all active (but none of load balance options ticked except notify switches) - so I guess Im asking how does the load balancing work? Is it working ?- How does it choose a NIC ? How does it work out which NIC is least used? what is MAc hash load balancing?

does a VM keep using the same physical NIC usually? - does it use a different one on each restart - thanks for doco - will read - Im hoping someone can give quick answer. thanks
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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
The VM will keep the same physical NIC, until restarted, or power-off, power-on. as each VM is switched on a new vmnic is used

e.g vmnic0, vmnic1, vmnic2 .....vmnic6

as for whether your load balancing is currently working....with no teaming policy or physical switch configuration - good question?

login to the physical switch, and check which MAC Addresses our on which switch ports, assuming you have more than a single VM, you should see (if load balancing) mac addresses on different physical switch ports.

if all mac addresses are on a single switch port, load balancing is not working.

the same can be seen, when using esxtop in network mode.

Route based on MAC hash or MAC address-based NIC teaming sends the traffic out of the originating vNIC’s MAC address.  This works in a similar way to the port-based NIC teaming in that it will send its network traffic over only one uplink.

see this screenshot

esxtop in network mode
various VMs, Test1 - Test10, using different network interfaces, vmnic0 - vmnic3, on vSwitch0

the above shows networking load balancing/teaming is being performed.
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philb19Author Commented:
hi yes i used esxtop - and it appears to have used various physical NICS - so even though options are not ticked - i is balancing

on another point :) - im looking for something to monitor a linux NIC - without using snmp - do you know of a way i can monitor network utilization quickly of a linux server ? - without full blown monitoring solution (snmp) ? - in linux is there a comand to show utilization - i don't manage the server but the DBAs say no graphic - all just unix shell . thanks
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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
Yes, if VMs are using different nics, it's load balancing.

on another point :) - im looking for something to monitor a linux NIC - without using snmp - do you know of a way i can monitor network utilization quickly of a linux server ? - without full blown monitoring solution (snmp) ? - in linux is there a comand to show utilization - i don't manage the server but the DBAs say no graphic - all just unix shell . thanks


- new question required, off topic here.
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philb19Author Commented:
ok posting now - thanks
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