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VSM and VEM Communication on a Local ESXi Host

Could somebody please explain the communication path between a VSM module and a local VEM?  The reason I ask is that our VM guy just performed a firmware upgrade on the ESX box, rebooted, and now the VSM isn't seeing any VEM modules and isn't communicating with the physical network (obviously).  The Management/Control/Packet configuration items within the VSM are still intact but the module isn't seeing the VEM installed on the same physical host.

Please correct me if I am wrong, but my understanding is that the VSM sends out a probe over the Control VLAN attempting to discover other VSMs and also to "bind" to its VEMs, correct?  I assume this is done via multicast or broadcast with the VEM "OID" specified in the VSM configuration encapsulated in these multicast/broadcast packets.  Within a single host, how do these packets pass between the VSM and the local VEM?  I understand it is the 1000V's job to do this, but there is some type of disconnect in my environment.  How does the VEM "know" what VLAN to listen to? 

I am trying to figure out exactly where the path is broken in my environment.  Anyone have any advice?

Thanks in advance for any assistance provided.



Everyone's tags (4)
Cisco Employee

Re: VSM and VEM Communication on a Local ESXi Host

Greetings Erik.

I'll assume your VSM's interfaces (Control/Mgmt/Pack) are hosted on the DVS.  If not, and you're using a Standard vSwitch - let me now.

The VEM is the local switch, so all the control information is broadcast to the VEMs on the "Control" VLAN.  This control VLAN is programmed through the opaque data pushed out by vCenter over the ServiceConsole/VMkernel interface.  This is "how" the VEM knows which VLAN to "listen" to for control information.  This also contains the Domain ID which uniquely identifies which DVS the Control informaiton belongs to.  If the Domain ID matches, the VEM responds to it, otherwise it simply drops it.

In your case the VSM is on the same VEM it's trying to communicate with so the VSM-VEM communication is all local (no upstream traversal).  Have you ensured the vEth Port Profile used for Control traffic is set as a "System VLAN"?  In addition to being set as a System VLAN in the vEth PP, ensure it's set on the Uplink PP as well.  If either of these are missing the VEM will not allow forwarding of any traffic for these interfaces, and your VEM will not be able to communicate with the VSM even hosts on itself.  Think of this as a catch-22.  You have to be able to forward certain VLANs in order for the VEM to receive it's programming from the VSM.  This is the role of a System VLAN.

If above doesn't catch your issue can you provide:

-You running config

Outputs from the VEM CLI (hosting the VSM)

vemcmd show port

vemcmd show trunk

vemcmd show bd

vemcmd show dr



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