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Bypassing the Hypervisor For Performance & Network “Simplicity” = Bypassing Security?

As part of his coverage of Cisco’s UCS, Alessandro Perilli from virtualization.info highlighted this morning something I’ve spoken about many times since it was a one-slider at VMworld (latest, here) but that we’ve not had a lot of details about: the technology evolution of Cisco’s Nexus 1000v & VN-Link to the “Initiator:”

Chad Sakac, Vice President of VMware Technology Alliance at EMC, adds more details on his personal blog:

…[The Cisco] VN-Link can apply tags to ethernet frames –  and is something Cisco and VMware submitted together to the IEEE to be added to the ethernet standards.

It allows ethernet frames to be tagged with additional information (VN tags) that mean that the need for a vSwitch is eliminated.   the vSwitch is required by definition as you have all these virtual adapters with virtual MAC addresses, and they have to leave the vSphere host on one (or at most a much smaller number) of ports/MACs.   But, if you could somehow stretch that out to a physical switch, that would mean that the switch now has “awareness” of the VM’s attributes in network land – virtual adapters, ports and MAC addresses.   The physical world is adapting to andgaining awareness of the virtual world…


Bundle that with Scott Lowe’s interesting technical exploration of some additional elements of UCS as it relates to abstracting — or more specifically completely removing virtual networking from the hypervisor — and things start to get heated.  I’ve spoken about this in my Four Horsemen presentation:

Today, in the VMware space, virtual machines are connected to a vSwitch because connecting them directly to a physical adapter just isn’t practical. Yes, there is VMDirectPath, but for VMDirectPath to really work it needs more robust hardware support. Otherwise, you lose useful features like VMotion. (Refer back to my VMworld 2008 session notes from TA2644.) So, we have to manage physical switches and virtual switches—that’s two layers of management and two layers of switching. Along comes the Cisco Nexus 1000V. The 1000V helps to centralize management but we still have two layers of switching.

That’s where the “Palo” adapter comes in. Using VMDirectPath “Gen 2″ (again, refer to my TA2644 notes) and the various hardware technologies I listed and described above, we now gain the ability to attach VMs directly to the network adapter and eliminate the virtual switching layer entirely. Now we’ve both centralized the management and eliminated an entire layer of switching. And no matter how optimized the code may be, the fact that the hypervisor doesn’t have to handle packets means it has more cycles to do other things. In other words, there’s less hypervisor overhead. I think we can all agree that’s a good thing


So here’s what I am curious about. If we’re clawing back networking form the hosts and putting it back into the network, regardless of flow/VM affinity AND we’re bypassing the VMM (where the dvfilters/fastpath drivers live for VMsafe,) do we just lose all the introspection capabilities and the benefits of VMsafe that we’ve been waiting for?  Does this basically leave us with having to shunt all traffic back out to the physical switches (and thus physical appliances) in order to secure traffic?  Note, this doesn’t necessarily impact the other components of VMsafe (memory, CPU, disk, etc.) but the network portion it would seem, is obviated.

Are we trading off security once again for performance and “efficiency?”  How much hypervisor overhead (as Scott alluded to) are we really talking about here for network I/O?

Anyone got any answers?  Is there a simple  answer to this or if I use this option, do I just give up what I’ve been waiting 2 years for in VMsafe/vNetworking?


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  1. March 19th, 2009 at 10:08 | #1

    It seems like you used to complain that virtualization breaks hardware security appliances; now that Cisco/VMware has unbroken them you're complaining that it breaks VMsafe. What do you want?

    Pragmatically, it will take a while for VMsafe to mature after it comes out, so the enterprisey enterprises are probably better off with UCS, no vSwitches, and their beloved hardware security appliances for a few more years.

  2. March 19th, 2009 at 10:49 | #2

    @Wes Felter

    So, one of two things has occurred, and I'm happy to accept either as the answer:

    1) I've done a bad job communicating my concerns, or

    2) You've done a bad job understanding them.

    Firstly, I've not "complained" that virt breaks hardware security, I've simply pointed that out and its attendant issues.

    Secondly, Cisco/VMware hasn't "unbroken" anything, they've squeezed the balloon and shifted where and how networking and some security functionality gets done.

    What do I want? I want the flexibility to be able to provide the level of protection commensurate with the profiles of the assets I'm protecting and ensure I understand the risks inherent with that flexibility.

    There will be a meet in the middle strategy (as there always is,) but I'll be honest…name one other person prior to my Four Horsemen presentation and VirtSec "…end of Network Security as we know it" talks from two years ago that highlighted the deficiencies of virtual appliances as a "solution" to this problem…

    Feel free to complain that I'm not happy with either solution because you're right, I'm not.

    However, I'm pretty sure given the feedback I've received that I've done more good than harm.

    To your last point, it's going to take a while for UCS to mature and since VN-Link and the 1000v is hitched to vNetworking (of which VMsafe is a component) the reality is that "pragmatically" UCS and no vSwitches ain't gonna happen overnight, either.


  3. PhilA
    March 19th, 2009 at 21:01 | #3

    Personally, I enjoyed the Cisco UCS references to Brock Lesnar a few posts ago. Somehow, MMA and Infosec go well together.

    Perhaps you may want to bring those references back up to clearly communicate your point to the average reader? Ok, just kidding.

    And no flexibility for you. You will like what the vendors give you as a solution and that's it.

    Another solid article.

  4. Paul
    June 28th, 2009 at 22:04 | #4

    This is all great in theory, but what about where I have Blade servers running virtual environments which themselves do some level of NIC virtualization (i.e. HP Flex10). Im sure i'm not alone when I say I see a LOT of customers are now just beginning to standardise virtual environments on Blades and I cant see that changing anytime soon (the large data companies we work with anyhow).

    Will HP/IBM support Palo on Cisco physical switches? Say for HP I guess it would mean updating Virtual Connect and maybe there'll bring out their own ProCurve equivalent and tie the whole lot together (a la UCS)

    I can see the benefits for sure, in terms of reduced hypervisor cycles, but until we have full cross vendor support for some of these things, it's a long way off

    Plus VM admins like vSwitches, they like the choices they have there and the ability to dedicate Port Groups to vLANS, seperate vSwitches out for vMotion, management etc. I think they'd want any physical switch representation to do something very similar

  1. March 18th, 2009 at 12:20 | #1
  2. April 12th, 2009 at 14:17 | #2