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From "" <>
Subject Understanding physical network mapping
Date Wed, 21 Nov 2012 17:43:57 GMT

First a quick background: 

I am trying to build a small "mini public cloud" that consists of 2 XenServer hosts and 1
management/nfs server. 

There is absolutely no need (at least on my end) for vlans or special isolation. 

Here is my setup: 

**Management / NFS Server** 
-> Ubuntu 12.04 LTS 
-> Two 1GB NICs assigned to br0 in a single bridge configured as (saves
me having to use another switch) 
-> One 1GB NIC configured with live IP of (yes - that's the actual IP)
and connected to public switch 
-> IP forwarding and MASQ enabled: <--> (tested, works)

-> DNSMasq installed, configured and working 
-> Entries in /etc/hosts for mgmt.mycloud, xen1.mycloud and xen2.mycloud 
-> Management server completely configured and ready 

** Two Physical Hosts** 
-> Each host has 2 GB NICs 
-> One NIC connected to public switch 
-> The other NIC connected to one of the two bridged ports on the management server 
-> XenServer 6.0.2 
-> Management Network configured via the interfaces 
-> xen1 is and xen2 is 
-> Neither xen host has a configured public facing IP, but each one IS connected to the

**Physical Router** 
-> Configured gateway IP is 
-> Connected [obviously] to public switch 

I initially did a very basic setup (basic networking) at first using only public IP addresses.
Everything worked, but of coarse, it uses like 8 or 10 IP's total. 

So I figured I would attempt a shot at advanced networking mode, with the following goals:

-> No need for special isolation 
-> Desire to "share" NFS and Management network ( 
-> Desire to provide VM's (instances) to the network on an as-needed
basis (not all will need access) 

My first issue I am having trouble coping with is getting a grasp on the "Physical Network"
to actual NIC mapping. This seems almost nonexistent. When I add a zone, I select "advanced"
and click next. I enter as [both] DNS servers and am imidiately confused by the
"Guest CIDR". Still not sure what exactly this should be - and examples online have further
added to this confusion. 

One example mentions using a arbitrary subnet ( - the default), and this is what
I have been doing thus far.. not sure if I am messing up at this point or not. 

Also, what is the "Public" checkbox for at this window? 

I click "next" and am brought to the Physical Network screen - with all the nice drag-and-drop
jquery stuff I am so fond of (nice touch guys). But this is perhaps one of the most confusing
parts there is. The documentation says each of these "Physical Networks" should "map" to an
actual NIC port on each xen host. How? I see an option to provide a free-form name to each
Physical Network (default for the first one is literally "Physical Network 1"). Where/how
to I tell cloudstack that "Physical Network 1" belongs to (or should be "connected to") port1/eth1/xenbr1
of the host? 

Also, is this the point at which I should define 2 physical networks and drag the yellow and
green icons to the bottom (Physical Network 2) and leave the blue one on "physical network
1"? I also assume I do not need to drag the red icon over into "Physical Network 1" since
they are the same subnet - correct? 

Next, the "edit" button on each icon.. Mentions "XenServer traffic label" - is this the uuid,
network-uuid or device value from "xe pif-list"? Or is this the actual device or bridge name
such as eth1 or xenbr1? Or is this something entirely different? 

Before leaving this step, I also wonder: why does it make me choose VLAN/STT/GRE? Can I not
have a simple non-vlan physical network? I am providing the isolation be means of the physical
network itself. Am I gonna have to bite the bullet and use VLAN-enabled switches for this?
Perhaps I can limit any VLAN-needs to trunk across the network since that does
not use an external switch and would be simple to mange? 

On the next screen that follows, it asks to set up the "public" network.. **sigh** more confusion...
Should I enter the details here? Or should I be entering something from
the network? 

On the next screen, we configure the Pods.. I am pretty sure at this point I need to simply
provide the gateway and an un-used range on the net - correct? 

The next screen takes me to a VLAN range window.. again - do I really need to? I am trying
to avoid VLAN's like the plague . 

I understand "Adding a host" well enough, but if someone intemately familiar w/ CS could shed
some light on the questions above, that would be excellent. 

One last consideration: not that I am anti-VLAN, but it is possible I will have to set up
and semi-manage over 50 such "mini public cloud" deployments and therefore I really need to
keep the overall deployment of each as simple as possible. I have a rather good understanding
of networking and XenServer in general and would have typically done this via normal XenCenter,
but rather have the CS GUI for end-users. 

Many thanks in advanced! 

- Dean 

Dean M. Rantala 
Upper Cumberland IT 
IT Consultant 
(931) 284-7384 
(931) 268-0037 

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