[ovirt-users] newbie questions on networking

[Rue, Randy]

Looks like the physical interface on the host and the virtual interface 
on the VM are both at the default 1500 MTU.

How can I determine the MTU setting for the physical switches without 
admin access to them? Or do I need to ask the network team?



On 5/7/2018 2:03 PM, Clint Boggio wrote:
> Randy this flaky layer two problem reeks of a possible MTU situation between your oVirt switches and your physical switches.
>
>> On May 7, 2018, at 3:59 PM, Dominik Holler <dholler at redhat.com> wrote:
>>
>> On Mon, 7 May 2018 11:43:51 -0700
>> "Rue, Randy" <randyrue at gmail.com> wrote:
>>
>>> I've sort of had some progress. On Friday I went to the dentist and
>>> when I returned, my VM could ping google.
>>>
>>> I don't believe I changed anything Friday morning but I confess I've
>>> been flailing on this for so long I'm not keeping detailed notes on
>>> what I change. And as I'm evaluating oVirt as a possible replacement
>>> for our production xencenter/xenserver systems, I need to know what
>>> was wrong and what fixed it.
>>>
>>> I reinstalled the ovirt-engine box and two hosts and started again.
>>> The only change I've made beyond the default is to remove the
>>> no-mac-spoofing filter from the ovirtmgmt vNIC profile so there are
>>> no filters applied. At this point I'm back to an ubuntu LTS server VM
>>> that again, is getting a DHCP IP address, nameserver entries in
>>> resolv.conf, and "route" shows correct local routing for addresses on
>>> the same subnet and the correct gateway for the rest of the world.
>>> The VM is even registering its hostname in our DNS correctly. And I
>>> can ping the static IP of the host the VM is on, but not the subnet
>>> gateway or anything in the real world.
>>>
>> Can you ping the DHCP server?
>>
>>> Two things I haven't mentioned that I haven't seen anything in the
>>> docs about. My ovirt-engine box is on a different subnet than my
>>> hosts, and my hosts are using a bonded pair of physical interfaces
>>> (XOR mode) for their single LAN connection.
>> Was the bond created before adding the hosts to oVirt, or after adding
>> the hosts via oVirt web UI?
>> If the switch requires configuration for the bond, is this applied?
>> Can you check if the VM can ping the getaway, if you use a simple
>> Ethernet connection instead of the bond?
>>
>>> Did I miss something in the docs where these are a problem?
>>>
>>> Dominik, to answer your thoughts earlier:
>>>
>>> * name resolution isn't happening at all, the VM can't reach a DNS
>>> server
>>>
>>> * I don't manage the data center network gear but am pretty sure
>>> there's no configuration that blocks traffic. This is supported by my
>>> temporary success on Friday. And we also have other virtualization
>>> hosts (VMWare hosts) in the same subnet, that forward traffic to/from
>>> their VMs just fine.
>>>
>> OK, L3 seems to work now sometimes.
>>
>>> * tcpdump on the host's ovirtmgmt interface is pretty noisy but if I
>>> grep for the ubuntu DDNS name I see a slew of ARP requests. I can see
>>> pings to the host's IP address, and attempts to SSH from the VM to
>>> its host. Any attempt to touch anything past the host shows nothing
>>> on any interface in tcpdump, not a ping to the subnet gateway, not an
>>> SSH attempt, not a DNS query or a ping to known IP address.
>>>
>> The outgoing ARP requests looks like the traffic of the VM is forwarded
>> to ovirtmgmt.
>> Do you see ARP reply to the VM?
>> Maybe the VM fails to get the MAC address of the gateway.
>>
>>> * hot damn, here's a clue! I can ping other oVirt hosts! (by IP only)
>>> I also tried pinging the ovirt-engine box, wasn't surprised when that
>>> failed as the VM would need to reach the gateway to get to the
>>> different subnet.
>>>
>>> So it appears that even though I've set up the ovirtmgmt network
>>> using defaults, and it has the "VM Network" option checked, my
>>> logical network is still set to only allow traffic between the VMs
>>> and hosts.
>>>
>>> What am I missing?
>>>
>>> -randy
>> _______________________________________________
>> Users mailing list
>> Users at ovirt.org
>> http://lists.ovirt.org/mailman/listinfo/users
>>