Re: [Xen-API] CPU Masking, VLAN/OpenVswitch, and pool member removal

[James Bulpin <James.Bulpin@xxxxxxxxxxxxx>]

Alex O'Ree wrote:
> Open vSwitch/VLANs. If I have two hosts (connected via a switch) in a
> pool, each with a guest assigned to the same VLAN, what do i need to
> do in order for them to communicate. If both guests run on the same
> host, they can communicate without any issues. I was under the
> assumption that when pooling machines, there effectively is a single
> vswitch that is pool wide. From my experiments, I'm assuming that this
> is incorrect and that additional work needs to be done. Is there a how
> to guide for setting this up?

In this kind of configuration the vswitch instance on each host will act
as an independent Ethernet switch. Therefore with your physical switch
linking the two servers you effectively have three Ethernet switches
between VMs on different hosts. If you are using VLANs then you need to
ensure that the entire path between VMs will carry the tagged VLANs.
This means:

  1. You need VLAN networks/PIFs defined on each server - I assume you
     have this already based on "each with a guest assigned to the same
     VLAN"
  2. The physical switch needs to be configured to pass the *tagged*
     VLAN between the ports the two servers are connected to. This can
     Be achieved various ways such as by setting up VLAN trunking - see
     your switch docs.

> I was under the
> assumption that when pooling machines, there effectively is a single
> vswitch that is pool wide.

You may be thinking of a "DVS" - i.e. distributed vswitch - this is
where vswitches use OpenFlow to communicate with a central DVS controller
to create the impression of a logical single pool-wide switch (with
inter-host traffic going via tunnels if necessary). This requires a DVS
controller as well as vswitches - XCP 1.6 doesn't come with one of those.

Regards,
James

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