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From Bryan Whitehead <>
Subject Re: KVM network flood
Date Mon, 05 Nov 2012 21:17:46 GMT
On Thu, Nov 1, 2012 at 6:14 AM, Trevor Francis <> wrote:

> I have gone through multiple iterations of my setup over the past 2 months
> with support from the IRC channel and cannot overcome a network flood. I
> have changed bonding modes, switch ports, complete switches, network
> topology and anything else I can think of to fix this issue. Here is what
> happens.
> - I currently have CS 3.02 running on KVM hypervisors.
> - My host machines have 6 nics. Those nics are split into 2 bonds
> (management and guest) physical networks. There are 4 bonds in guest and 2
> bonds in management. Public and guest traffic go over guest network on 2
> separate VLANS and management/storage goes over the management physical.
> - The 2 bonds management are split between 2 trunked switches (for fault
> tolerance at the switch level). The 4 bonds on the guest network are split
> between 2 trunked switches, so there is a total of 4 switches in my
> network. The guest network switches have hsrp uplinks to our core router
> for internet services.
> - I have spanning tree enabled on the switches and on the cloud bridges as
> well as the VLANs in the switches.
> - I have enabled advanced networking.
Each port on the switch needs to be in trunking mode so when a new vlan is
added/created it will work. you can spanning-tree portfast on the ports for
the server(s).

the port interconnecting the switches also need to be in trunking mode so
vlans created can propagate.

> To allows a private network (guest) and a public network (shared public)
> to be bound on separate ethernet interfaces for my guest VMs (eth0 and
> eth1), I create a default isolated network for the guest network and
> creates a shared public network for the public network. Guest network is on
> VLAN 11 and public is on VLAN 10.
> The storage network works fine, no floods, nothing unusual. (For all
> intents and purposes the network is configured exactly like the guest
> network, with 2 less interfaces in the bond).
> The isolated guest network works fine as well, nothing unusual. However,
> when I spin up an instance that I have a public network bound to, the flood
> begins. It is interesting to note the the flood begins from the VR and not
> the guest. As soon as the VR is spun up, it starts flooding. If I create a
> shared network WITHOUT utilizing any services requiring the VR, the network
> will come up fine...but I have to manually add an IP address to the machine
> instead of letting the VR assign it through DHCP. I created a new NO for
> the shared network I am using and only selected DHCP as the services
> offered....same issue happens with flooding.
> I am at my wits end here and dont know how to resolve this. Has anyone
> else had this issue?
> I use network bonding myself. What mode are you using for your bonded

However I've simplified mine to just using eth0/eth1. My ifcfg-bond0 looks
has this:
BONDING_OPTS="mode=1 primary=eth0 miimon=1000"

If you are using an alternative bonding mode this has to be fully supported
by your router/switches. I've never had usable success with with mode 2, 3,
5, and 6.

I've found mode 4 requires the bonded nics to be plugged into the same
switch for 802.3ad to correctly work. Maybe your switches are fancy enough
- but I'd take a look at that.


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