[ovirt-users] Confused by logical networks

[Vincent Royer]

I had similar confusion, and trying to assign static IPs was just not
working for me.

Here is how I got it to work:

#1 you absolutely require a DNS server you can add entries to.  I tried to
go without, and it just does not work.

For me, management network is on vlan 10, so each host grabs a 172.16.10.xx
address.  The oVirt engine (self hosted) also grabs an address in this
subnet. I look in the DHCP leases and turn those into static assignments in
the router, but left the config on the hosts to DHCP.  Add those IPs to
your DNS so that you can reach each host, and the engine, at
hostname.domain.net (or whatever your fully qualified domain name is for
each)

Now, set your VM network to DHCP on a different, specific VLAN.  Set that
vlan up in your router with a small DHCP pool, only big enough for the VMs
you want to run. Make sure you allow that vlan through to the switchports
connected to the nic you are using for your VMs.

For me, the VMs are on vlan 30, so the subnet is 172.16.30.xx. Each VM
boots up, makes a DHCP request on vlan 30, and is assigned an address.
Then again go into your router and make this a static entry, leaving the
config in the VM to DHCP.  Once you install the agent in the VM, the IP
will show up in the engine GUI.  Then you can assign an FQDN to each vm's
IP I'm your DNS server.

Set up this way, I can migrate the VM to whichever host, and still access
it over RDP by it's FQDN.

I also have dual NICs but I set mine up as a team (bridge) instead of one
for MGMT and one for VMs.   That way, I can also unplug anyone Ethernet
cable from any machine, and nothing happens, both the MGMT and VM network
keep ticking away happily.  I have each NIC plugged into a separate switch
chassis, to gain redundancy on the switches.

Hope some part of this helps you!


On Feb 22, 2018 7:25 AM, "Paul-Erik Törrönen" <poltsi at poltsi.fi> wrote:

> I'm not sure how the logical networks should work and would appreciate if
> someone could shed some light into the matter, I've tried reading the
> documentation¹ but have not become any wiser :-/
>
> For the sake of argument, I have two hosts in the same cluster/DC, They
> both have 2 network devices each (let's call them eth0 and eth1). On both
> hosts the ovirtmgmgt is connected to eth0 and uses the 10.0.0.0/8-network.
> Host 1 is 10.0.0.1 and host 2 is 10.0.0.2. All four network devices are
> connected to one switch.
>
> Then I create a logical network, mylogic which should be 192.168.1.0/24,
> which I assign to eth1 on each host, but define only for host 1 an
> ip-address, 192.168.1.1, host 2 has also the network assigned to eth1, but
> withouth an ip address.
>
> Next I create vm1 on host 1, give it a single virtual network connection
> to mylogic, and configure the guest to use 192.168.1.2 with gw 192.168.1.1.
> Obviously I can from the guest ping 192.168.1.1 which is the host address
> on the logical network as the guest is running on the same hardware where
> the host ip address is defined.
>
> However, and this is where my confusion lies, if I now create another vm,
> vm2, on host 2, attach its network device to the mylogic network and
> configure it to use 192.168.1.3 with gw 192.168.1.1, I can not ping neither
> 192.168.1.1 nor 192.168.1.2.
>
> My understanding is that vm2 should be able to ping the wm1 as well as the
> gateway address defined on host 1. However this does not seem to be the
> case.
>
> What have I missed here?
>
> TIA,
>
> Poltsi
>
> ¹ https://www.ovirt.org/documentation/admin-guide/chap-Logical_Networks/
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>
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