[libvirt-users] Routed mode problem with SSH

[Laine Stump]

On 11/22/2016 02:09 PM, Marcelo Palma wrote:
> Hi guys, I  describe the context of the problem below:
>
> I installed a Tor relay on a virtual machine on my server with IP 
> 9.1.1.101. This virtual machine needs to use a static IP (9.1.1.102) 
> to work as a Tor relay. After that I create a virtual network in 
> *Routed mode* to connect to the physical network (used as a bridge 
> between the virtual machine and the external network (Internet)).
>
> Since I change the NAT to Routed mode, I can't access my server via 
> ssh user at 9.1.1.101 <mailto:user at 9.1.1.101>.

First let's make sure we're talking about the same things. Here is what 
I *think* you're describing:

* Previously you had a virtual machine (I'll use the word "guest") that 
was connected to a <forward mode='nat'> libvirt network, and the you 
were able to connect to the physical machine (I'll call it "host") with 
"ssh user@[some IP address]".

* Now you have created a libvirt network with <forward mode='route'>, 
and given the guest the IP address 9.1.1.102. One of the host's 
interfaces is 9.1.1.101, and "ssh user at 9.1.1.101" doesn't connect.

If that's all correct, then here are my questions:

What is the IP address and netmask (or prefix) for the libvirt network? 
Is is 9.1.1.101? If not, and if that IP is on the physical ethernet 
device of the host, then you're trying to put the libvirt routed network 
on the same subnet as the physical network, which is not the intended 
use for mode='route'.

The idea of mode='route' is that you have a separate subnet that is 
fully contained in the host, and the host uses IP  routing to forward 
traffic between that "virtual" subnet and the physical network. This is 
only useful if you have enough control over the physical network to add 
a routing table entry that points external traffic for the virtual 
network towards the physical adapter on the host.

If that's not what you want, and what you really want is for the guest 
to be on the same subnet as the physical network, then you need to 
create a host bridge device outside of libvirt, and directly attach the 
physical ethernet device on the host to that bridge. Then you will 
attach the guests' interfaces to that bridge. There are instructions for 
creating a bridge device on various distros here:


https://wiki.libvirt.org/page/Networking#Host_configuration_2

>
> Will it be a Routed mode problem?

My first suspicion is that you've misunderstood the purpose of <forward 
mode='route'> networks. If not, then provide more information (e.g. the 
IP address of the host's physical ethernet, the full XML of the virtual 
network you created, the <interface> section of the guest's 
configuration) and we can try to troubleshoot further.

>
> How can I solve this problem?
>
> Thank you
> Marcelo
>
>
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