VMware vSphere

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  • 1.  Maximum Number of vLANs to trunk

    Posted Nov 26, 2012 09:13 PM

    What are some guidelines for deciding how many vLANs I should trunk to an ESXi host?  If I trunk too many vLANs, then too much broadcast traffic goes to my host clogging my available bandwidth on the hosts NICs.   Supposing I have 250 VMs per VLAN / subnet, are there some best practices / configuration maximums for when I need to stop trunking any more vLANs to my hosts?   I know the vSwitches support > 4000 vLANs but when will all the broadcast traffic start to overwhelm my physical NICs and CPUs?  I know the answer is workload and environment dependent but if there are any examples or guidelines you have discovered feel free to share.  Thanks.



  • 2.  RE: Maximum Number of vLANs to trunk

    Posted Nov 27, 2012 01:22 AM

    It would stand to reason that if you had enough VLAN broadcast traffic to saturate an ESXi host, the physical switch environment would also be quite loaded (since it receives all of the broadcast traffic in an environment that does not utilize something like VTP pruning). That being said, I have not encountered such a situation where broadcast traffic has negatively impacted ESXi hosts in an enterprise environment spanning several thousand VMs across a few hundred VLANs. There are also physical switch options, such as storm control, that can limit the exposure vulnerability to broadcasts on your trunked interfaces.

    I don't think there are any hard and fast numbers that anyone could provide. Even "from experience" examples would be mostly unique to the experience and environment. If you grow to a size where there are a large volume of VMs talking to a large quantity of VLANs, you gain the ability to design around application groups based on VLAN. Considering that there is a finite number of VMs that can be placed on a host (both physically and for risk aversion), this becomes easier as an environment scales.



  • 3.  RE: Maximum Number of vLANs to trunk

    Posted Dec 03, 2012 02:37 PM

    Thanks for the input.  So if I have 4 clusters with 15 small form-factor blade servers each, and it is easier from an administrative standpoint to trunk all vLANS to all hosts of all clusters, and broadcast traffic doesn't become an issue, it might be an OK design decision rather than separating groups of vLANs to be trunked to a single cluster?



  • 4.  RE: Maximum Number of vLANs to trunk

    Posted Dec 03, 2012 03:06 PM

    I would agree with that. Really it comes down to a trade off between administrative overhead and security. Strictly speaking, you should only trunk the vlans you need, but managing that can quickly become time consuming if you have a lot of network changes.