Re: [Xen-devel] Best way to get IP addresses from VMs without logging in to them?

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 11/06/14 17:38, Ian Campbell wrote:
> On Wed, 2014-06-11 at 12:32 -0400, Russ Pavlicek wrote:
>> I have been working on an "on-ramp" application to introduce new
>> people to Xen Project (more on that later), when I ran into a simple
>> scenario which seems to lack a simple solution:
>>
>> When I start up a new VM which employs DHCP, how can I
>> programmatically determine what IP address it obtained?
>>
>> When I look at the Wiki, I find the following reference:
>>
>> http://wiki.xenproject.org/wiki/Xen_FAQ_Networking#IP_Determination
>>
>> Which suggests using tcpdump for sniffing out packets relating to a
>> known MAC address.  But that depends on traffic flow from VM, which
>> could be time consuming if the machine happens to be idle.
> If the machine is using DHCP then you should be able to observe the DHCP
> requests and responses, which contain the IP address. I think Xenrt does
> something around parsing the tcpdump output of that happening, but I'm
> not sure of the details.
>
> Ian.

I believe XenRT snoops ARP and DHCP packets from dom0 using tcpdump, but
also controls the DHCP server itself.

XenServer also has the guest tools package.  This is a small daemon
running in the guest which, amongst other things, writes
/local/domain/$DOMID/attr/eth$N/ip/$DETAILS which is then consumed by
monitoring tools in dom0.

~Andrew

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