DHCP trusted ports, with virtual machines?

[Stephan Romano]

I have a Cisco 4506 switch with a cluster of VMWare ESXi servers attached to it. The DHCP server for this network is in one of the virtual machines, so I have the uplink ports to the cluster all set to trusted.

This is okay for the time being, but I do not micromanage all of the virtual machines in this cluster, and I am concerned that someone could accidentally start serving DHCP out of one of the other virtual machines in the cluster. Since the ports for the whole cluster are trusted, the switch would not stop it - and in fact, in some cases, the other VMs are legitimately handing out DHCP in other VLANs.

How do I ensure the switch will block DHCP that is not sent from a specific server? With the popularity of VMs, I can't be the only one who has this problem but my Google-fu seems to be failing me on finding an answer.

[Lei Tian]

Hi Stephan,

Nexus 1000v should give what you are looking for. N1Kv is virtual distributed switch inside the hypervisor, you can config it like regular switch; it has most security features needed on normal Cisco switch.

HTH,
Lei Tian

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[Stephan Romano]

Thanks Lei.

So there's no way to configure the physical switches to do this?

I found it interesting that the few HP ProCurve switches we have scattered around all include the ability to trust a DHCP server's IP address instead of only trusting a specific port. Of course, that is less protection against a malicious attacker, but it sure is useful to prevent accidental/nuisance problems which, in the network I'm working with right now, is far more likely than a directed attack.

Of course, I have plenty of other things I don't like about the ProCurves, which is why they're not in the core, but it's a useful feature when deployed carefully.

[Lei Tian]

Hi Stephan,

I don't think dhcp snooping trust IP is supported on the switch. But most virtual switch vendor, Cisco, VMware and hyper-v all support dhcp snooping.

For new feature request, please contact your Cisco account team with the biz requirement.

HTH,
Lei Tian

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