Open Stack

Hey all,

we're pretty happy about our new OpenStack Essex installation atop of
Ubuntu 12.04 (hypervisor and guests).
We use KVM (tenant is in a VLAN) as virtualization technology, having about
15 compute nodes, and a
central nova-network node to act as the gateway (yet to be fully HA'd,
however). On that gateway we're having
a PPTP VPN so we can log in on any host or guest though this VPN.

Our problem however is, that from time to time (I think it's daily and even
multiple times per day)
we're encountering kind of networking freezes.

I first noticed it as my SSH session froze for a few seconds from my
desktop -> VPN (nova-network node) -> KVM guest.
I quickly checked others, and they hang, too.
I checked a hypervisor, which didn't hang, so it is not a general
networking issue (like PPTP or SSH or alike).

Now, it feels like there is some problem with networking from and/or to KVM
guests and I absolutely have no clue
on how to trace this down. It really feels like a bug, but that's really
out of my scope, and that's why I'm seeking for advice here,
since we just can't stay in this situation :-)

It is confirmed that we're having this from desktop -> VPN -> KVM and from
physical node (in data center) to KVM.
However, I do not yet know whether all KVMs are affected at once (which
would indicate that the issue MAY be caused
by the central nova-network node) or whether it is just hypervisor based
(so it may be due to some hypervisor's state)
or just plain random across all 15 compute nodes we have.

I now think that this issue may indeed be KVM networking related

I'll be happy about any hints and proposals you can provide me in order to
track this
issue down.

Please tell me about any further information you need.

Many thanks in advance,
Christian Parpart.
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