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From Ove Ewerlid <Ove.Ewer...@oracle.com>
Subject Re: Doubt abou link local
Date Wed, 28 May 2014 14:51:59 GMT
communication is between KVM hypervisor and system VMs running on that 
same hypervisor. All ACS KVM hypervisors have a bridge called "cloud0" 
with an IP from the special link-local subnet;
  http://en.wikipedia.org/wiki/Link-local_address
meaning that no routing ever takes place in/out of this subnet.

The bridge cloud0 is thus used for communication between the hypervisor 
host and the system VMs on that same host and all of those have one NIC 
connected to the "cloud0" bridge, same broadcast network.

NB; there is a global parameter to set the size of the subnet from where 
link local IP's are allocated randomly. (linklocalip.nums)

To use SSH to access a system VM you must login to the the KVM host 
running that system VM and issue a command similar to this as root;

  ssh -i ~/.ssh/id_rsa.cloud -p 3922 
<ip-of-system-vm-derived-via-api-or-other-method>

a CLI oriented method to get the IP's used by systemvms on a host is to 
use nmap, e.g.,;
   nmap -sP 169.254.0.0/22
(that will take some time, tweak options to nmap for more speed or 
reduce the size of the link local subnet).

Perhaps that removes some doubts :-)

/Ove


On 05/28/2014 04:21 PM, Ana Paula de Sousa wrote:
> Hi,
> I would like to know if link local is created in cloudstack as a bridge, if
> so, it's between hypervisor and what? If no, can you explain to me what is
> link local (i know it's made to comunicate the VMs and the hypervisor, but
> how?)
>
> Thanks.
>


-- 
Ove Everlid
System Administrator / Architect / SDN- & Automation- & Linux-hacker
Mobile: +46706668199 (dedicated work mobile)
Country: Sweden, timezone; Middle Europan Time (MET or GMT+1)

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