On 11/28/2012 05:34 AM, Roni Luxenberg wrote:
----- Original Message -----
From: "Itamar Heim" <ih...@redhat.com>
To: "Dan Kenigsberg" <dan...@redhat.com>
Cc: "Alon Bar-Lev" <alo...@redhat.com>, "VDSM Project Development"
<vdsm-devel@lists.fedorahosted.org>, "Yaniv Kaul"
<yk...@redhat.com>
Sent: Wednesday, November 28, 2012 11:01:35 AM
Subject: Re: [vdsm] Future of Vdsm network configuration - Thread
mid-summary

On 11/28/2012 03:53 AM, Dan Kenigsberg wrote:
On Tue, Nov 27, 2012 at 03:24:58PM -0500, Alon Bar-Lev wrote:




Management interface configuration is a separate issue.

But it is an important issue that has to be discussed..

If we perform changes of this interface when host is in
maintenance
we reduce the complexity of the problem.

For your specific issue, if there are two interfaces, one
which
is
up during boot and one which is down during boot, there is no
problem to bond them after boot without persisting
configuration.

how would you know which bond mode to use? which MTU?

I don't understand the question.

I think I do: Alon suggests that on boot, the management
interface
would
not have bonding at all, and use a single nic. The switch would
have to
assume that other nics in the bond are dead, and will use the
only
one
which is alive to transfer packets.

There is no doubt that we have to persist the vlan tag of the
management
interface, and its MTU, in the extremely rare case where the
network
would not alow Linux's default of 1500.

i was thinking manager may be using jumbo frames to talk to host,
and
host will have an issue with them since it is set to 1500 instead
of
8k.
jumbo frames isn't a rare case.

as for bond, are you sure you can use a nic in a non bonded mode
for
all
bond modes?


all bond modes have to cope with a situation where only a single nic is active 
and the rest are down,
so one can boot with a single active nic and only activate the rest and promote 
to the desired bond mode upon getting the full network configuration from the 
manager.

of course they need to handle single active nic, but iirc, the host must be configured for a matching bond as the switch. i.e., you can't configure the switch to be in bond, then boot the host with a "single active nic" in a non bonded config


Changing the master interface mtu for either vlan or bond is required
for management interface and non management interface.

So the logic would probably be set max(mtu(slaves)) regardless it is
management interface or not.

I discussed this with Livnat, if there are applications that access
the master interface directly we may break them, as the destination
may not support non standard mtu.

This is true in current implementation and any future implementation.

It is bad practice to use the master interface directly (mixed
tagged/untagged), better to define in switch that untagged
communication belongs to vlanX, then use this explicit vlanX at
host.

next, what if we're using openvswitch, and you need some flow
definitions for the management interface?

I cannot answer that as I don't know openvswitch very well and don't
know what "flow definitions" are, however, I do guess that it has
non persistent mode that can effect any interface on its control. If
you like I can research this one.

you mainly need OVS for provisioning VM networks so here too you can completely 
bypass OVS during boot and only configure it in a transactional manner upon 
getting the full network configuration from the manager.

a general question, why would you need to configure VM networks on the host 
(assuming a persistent cached configuration) upon boot if it cannot talk to the 
manager?
after-all, in this case no resources would be scheduled to run on this host 
until connection to the manager is restored and up-to-date network 
configuration is applied.

thanks,
Roni


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